The Apiaceae family includes several vegetables, most notably carrots and celery, that are widely consumed by many cultures around the world. It also includes several of the most prominent herbs—dill, cilantro, fennel, and parsley—used to flavor dishes in many cuisines. The plants of this family, formerly known as the Umbelliferae, all share an inflorescence in the form of a compound umbel, so named for its umbrella-like appearance. The small perfect flowers are borne on small umbellettes, with pedicels that arise from a single point, which is in turn attached to larger pedicel rays that are joined at the apex of the flower stalk (hence its compound nature). All members of this family have leaves, flowers, seed, and roots that are aromatic due to volatile oils that impart very distinctive flavors to the cultivated members.
The Apiaceae are all dry-seeded crops, and their seed is most successfully grown when there is little or no precipitation during the flowering and seed maturation process. Almost all of the commercial seed production for the most widely grown Apiaceae crops—carrot, celery, and parsley—takes place in temperate regions with dry summers, the so-called Mediterranean climate. However, smaller-scale seed production of regionally important varieties of these crops, as well as production of unusual vegetables in this family like celeriac and parsley root, is widespread in places like Eastern Europe and Asia Minor (and many carrot varieties throughout Asia). And while there is considerable seed produced commercially of the minor Apiaceae herb crops such as cilantro, dill, cumin, and fennel, much of the seed for these crops is grown regionally for sale and subsistence use across Southern and Eastern Europe, northern Africa, and all of Asia.
Family Characteristics
Reproductive Biology
The cultivated Apiaceae include both annuals and biennials and consist of dry-seeded crops that most successfully mature their seed over an extended dry period in late summer and early fall. The cultivated Apiaceae have perfect flowers with five stamens, five petals, and five sepals. They are largely cross-pollinated due to insect activity but can also self-pollinate. However, a number of important crops in this family, including carrot, celery, cilantro, and parsnip, have an elegant device to discourage inbreeding. On any particular flower the fertile pollen will shed before the female stigma is sexually receptive, thus decreasing the chances of a self-pollination on that flower, thereby increasing the chances that pollen from that plant will only pollinate the receptive stigma of a slightly older flower on another plant. This is important as some species in this family, most notably carrot and celery, frequently suffer from inbreeding depression.
The primary or king umbel of a carrot plant in full flower.
The flowering pattern of most of the crop species in this family is distinct. It begins with one central inflorescence borne at the terminus of the main floral stem, which is known as the primary or king umbel in carrot. This is followed by secondary umbels that are located at the terminus of the branches arising from the main stem. In most temperate climates the seed borne on the flowers of the primary and secondary flowers is the seed that most reliably matures. Depending on the length of the growing season, subsequent third- and fourth-order umbels will form, but the opportunity for the seed to fully mature on these later-setting flowers is greatly reduced in most temperate locations. The ovary of most of the cultivated crops in this family has two locules, each producing a separate seed. This pair of seeds is joined at maturity. In crops such as carrot, celery, and parsley these paired seeds easily separate when the seed is threshed and cleaned. But in a crop like cilantro they remain joined as a round seed ball, which is preferred by many for ease of planting but often results in two tightly spaced seedlings when the germination rate is high.
Seedling emergence and early seedling growth is notoriously slow in most crops of the Apiaceae. Also the days to germination and initial growth rate of the seedlings can vary quite a bit from seed to seed within a given variety and even within a particular seed lot. Research in carrots suggests that seed from the primary and secondary umbels that is uniformly mature and of a high germination rate will produce seed that germinates more uniformly than seed produced by later-appearing umbels, in less time, and ultimately producing a more uniform stand of carrots. This is probably true with other crops in the Apiaceae, all of which have the same flowering pattern. Seed growers working with these crops must be conscious to harvest the most mature seed possible without exposing the crop to excessive wind and rain.
Life Cycle
The vegetable crops of the Apiaceae are usually biennials, while herbs such as dill and cilantro have an annual life cycle. When grown as a seed crop the biennial vegetables are routinely direct-seeded sometime during midsummer of the first year to produce the first year’s storage root. The goal is to produce a moderate-sized root the first year that can then be stored, either in the ground or in a root cellar or cooler for replanting the following spring. Whether the Apiaceae crop is a leafy crop like celery or parsley, or a traditional root crop such as carrot, celeriac, or parsnip, it is very important to have a substantial root with an intact growing point to survive the long storage period and vigorously grow in spring.
There are three methods used for overwintering biennial Apiaceae crops:
1. Plant the crop in the field of intended seed production. Overwinter the crop in the field with flowering and seed production in situ in Year 2.
2. Grow the crop in a nursery plot in the first year; lift the roots or plants in the fall, transplanting them to overwinter in next year’s seed production field.
3. Grow the crop in a nursery, lifting it in the fall for storage in a root cellar or cooler until replanting it to the field in the spring of Year 2 for seed production.
The advantage of the first method is that it doesn’t involve the time and labor of transplanting; however, it does require more land area in Year 1, as the crop is planted and thinned to the wider spacing that is required for seed production right from the beginning. For root crops such as carrots, celeriac, parsley root, and parsnip this method is known as the seed-to-seed method. The great disadvantage of using the seed-to-seed method with root crops is that you don’t get an opportunity to select for all of the root characters important to each particular crop (see each individual crop profile for a description).
The second and third methods for overwintering biennials use a nursery plot to raise the first-year plants before storing them or transplanting them directly for seed production in the second season. In general the nursery plot will only consume between a tenth and a fifth of the space of the seed production field, since the plants must be replanted at a wider spacing to accommodate the much larger flowering plants. Both of these methods when used with root crops are considered the root-to-seed method as the roots are lifted and selected before replanting for flowering and seed production. This gives the grower the ability to genetically maintain and improve the important root characteristics of these root crops.
The last major element to consider when choosing an overwintering method for seed production is to match the cold hardiness of the crop with the severity of your winter. Several of the prominent Apiaceae crops, including carrot, celeriac, parsley, and parsley root, are generally cold-hardy, if gradually hardened off, to temperatures of 15 to 20°F (–9 to –7°C). This also is largely dependent on the particular variety of each crop and the degree of freezing and thawing that occurs over the course of a particular winter season. Snow cover can ease this with its insulating effect; in essence it acts like a 32°F/0°C thermal blanket if fully covering the aboveground parts of the plant. Parsnips on the other hand can take temperatures down to about 5°F (–15°C) and possibly colder when overwintered, making them an even more forgiving candidate for the seed-to-seed method in many temperate climates.
Mature carrot seedheads.
The maturation of Apiaceae crop seed begins with the primary umbel and advances through the secondary and tertiary umbels over time. The timing of harvest involves a compromise on the grower’s part between harvesting the highest amount of mature seed and not waiting too long to harvest and thus risking the loss of quality to fall rains or loss of seed from shattering. While there are varied opinions as to precisely when to harvest the seed of these crops, growers have a variety of signs that they look for to determine maturity. In general the color of the seed is used as an important indicator of maturity. Most Apiaceae seed will turn an earthen shade of brown when mature. Some growers will harvest when the seed of the primary umbels is fully brown and the secondary umbels are midway in the process of turning brown. Others wait until both primary and secondary umbels are brown and the tertiary umbels are turning brown. Some growers judge maturity based on when seed on the primary umbels starts to drop. All of these maturity guides depend on the crop species and the climate in which they are being produced. Most importantly, each grower must get to know the relative maturity of the crop species as well as the specific variety for their climate. Then it is possible to know when to harvest the crop before losses from fall precipitation or shattering of the most mature seed from the primary umbel occurs.
At harvest maturity Apiaceae seed crops are usually swathed and laid in windrows on cleared, cultivated ground or on tarps to allow for further drying and finishing (final maturation of the seed). Windrows should not be piled higher than 2 ft (0.6 m) deep to allow for good airflow. Windrows should be allowed to cure for 5 to 10 days during warm, dry weather. If poor weather threatens and the crop is not too large, then placing the crop in an airy barn or greenhouse may preserve its quality. In large-scale production, mobile combines are often used for the threshing and initial cleaning of the seed. For smaller-scale commercial production, seed is often threshed by manually feeding several plants at a time through a stationary plot thresher or into the header of a grain combine with a cylinder that has rubber-covered bars. Swathing and threshing are best done early in the day to take advantage of morning dew in reducing losses from shattering. Making sure that the plant material to be threshed is not too dry and brittle is also important in minimizing the excessive breakage of the plant stems, especially the small stem-like petioles of the umbellettes. These are easily broken into small pieces about the same size as the seed and can be very hard to clean out of the seed crop later in the cleaning process.
The seed of most Apiaceae crop plants have ribs that run the length of the seed. Carrot and dill have spines or beards that emanate from these ribs. If not debearded these spines can cause clumping of the seed in planters, especially precision planters. They are generally removed after the initial cleaning (scalping and screening particulates) by milling the seed with a decortication cylinder that gently rubs the beard free without damaging the seed. The removal of the fine, broken stems of the umbellettes is also required in order to produce a seed lot that will flow satisfactorily through most planters. A percentage of these stems can be removed by running the seed through a series of seed screens varying in either size or shape of the holes, or by winnowing. However, the smallest of these stems are best removed using a piece of equipment known as an indent cylinder. This device has a rotating drum with a series of indented depressions, which can catch the seed, while the larger stem pieces are eliminated. Final screening and sizing of the seed is then done. Sizing of carrot seed is extremely important to most discerning growers, as it ultimately influences the size and uniformity of the carrot roots.
Carrot
Carrot (Daucus carota L.) is one of the most recently domesticated of the common vegetable crops. The earliest conclusive documentation of the use of carrot as a vegetable is from the 10th century in present-day Afghanistan. From its center of origin in the Middle East the carrot spread north to Europe and east to China and Japan, presumably via the Silk Road, over the next several centuries. From the earliest documentation in the Middle East up until the 17th century in both Europe and Asia cultivated carrots were less refined than our modern crop and were either purple or yellow in color.
Paintings of kitchen scenes by European realist artists in the 17th century offer the earliest conclusive record of orange carrots. The arrival of an orange-rooted type, possibly as a variant of yellow, stimulated a rash of carrot breeding in Northern Europe, concentrating on improvements in the crop’s eating quality and on the intensity of orange color. The popularity of orange carrots grew quickly from this effort. White carrots also appeared in Europe at around this time and have remained popular in Belgium and France as a unique ingredient in soups and stews, as well as their use to feed farm animals. Orange carrots soon spread around the world; over time this has become the predominant color of carrots in most growing regions.
The orange carrot variety in the foreground is a uniform selection of ‘Nash’s Nantes’ that was harvested before full maturity (from Nash Huber’s farm stand at the Port Townsend Farmer’s Market). Photo courtesy of Micaela Colley
Carrots can be placed into two basic types. The western type, characterized as a cool season crop, which includes orange, white, purple, and yellow forms, originated in the Mediterranean basin and Europe. The second type, more often subtropical carrots, were grown and selected for centuries under the hot growing conditions in China, Japan, and Southeast Asia. The subtropical type may be yellow, purple to reddish purple, or red in color and usually has leaves with a fine pubescence and a grayish green color with leaflets that are less divided and more compound than the more common western type. They also have a propensity for early bolting or flowering before producing an edible root in both North American and European production areas. This has created a problem for seed companies wanting to improve some of these subtropical types with unusual colors for use in the temperate north. Selection to improve bolting tolerance will usually take several breeding cycles, especially if the breeders don’t want to narrow the genetic base of the population they are improving for this exceedingly important trait.
Ever since the onset of breeding work on orange types began, the other colored types have gotten little breeding attention and have often been relegated to a lower culinary use status or for use as fodder crops until very recently. For this reason many of the unusually colored carrots—purple, red, yellow, and white—have a more “rustic” raw carrot flavor, which is often more complex and less sweet but can be rife with off-flavors from the terpenoids (flavor compounds), which haven’t been tamed by plant breeding. Some breeding of these types that started in the 1990s has created some colored varieties that are more akin to our modern orange types, but breeding for flavor in carrots is not easy due to the complexity of this trait. For now, though, most of these colored types offer us an opportunity to rub shoulders with our ancestors and experience the rustic flavor of carrots as they tasted in the past!
Seed Production Practices
Climatic and Geographic Requirements
Carrots as a vegetable crop are produced over a wide range of environments, from the subtropics to cool climates in Northern Europe and southern Argentina. The production of good-quality roots requires fertile soil with a good deep tilth and an even supply of water throughout the season. The geographic and climatic requirements for carrot seed production are more exacting than for root production.
Geographically the carrot seed grower must be sure that there is no Queen Anne’s lace (Daucus carota var. carota) within a 1- to 2-mi (1.6- to 3.2-km) area of the potential production field (see “Isolation Distances”). This common weed, also called wild carrot, has spread to temperate climates around the world as an established weed. It is especially prolific in the eastern half of the North American continent (east of the 100th parallel) and in much of Europe, and it readily crosses with cultivated carrot. Indeed, P. W. Simon of the USDA has found that it frequently exchanges genes with cultivated carrot and is truly part of the carrot gene pool, for better or worse. Unfortunately, it universally carries the single dominant gene for white root color; it is very undesirable to allow it cross with your seed crop, as large “gnarly” white roots with many adventitious or branching roots will appear in the next generation.
In most regions where Queen Anne’s lace occurs it is so ubiquitous and evenly spread across the countryside that it is impossible to destroy all of the plants within a 1- to 2-mi (1.6- to 3.2-km) radius. The only effective way to produce pure carrot seed in the vicinity of Queen Anne’s lace is with well-maintained pollination cages equipped with a mesh material specifically designed for insect-pollinated crops. These cages are too expensive for commercial seed production and are generally only used by breeders or seed banks for research or preservation needs, respectively. To produce high-quality carrot seed commercially it is imperative to grow the crop in a geographic area free of this weedy variant of cultivated carrot.
The best climate for carrot seed production includes a fairly mild spring and a dry summer with temperatures that routinely reach 85°F (29°C) and above, but generally don’t reach temperatures above 92 to 95°F (33 to 35°C) until late in the summer, after the seed is set and maturing. As for all dry-seeded vegetable crops, a dry, Mediterranean climate with low precipitation amounts from late June until mid-September is best, because it significantly lowers the chances of any diseases forming on the seedheads as they mature. However, this means that there needs to be reliable water applied with either a drip or furrow irrigation system; overhead irrigation may promote disease in the seedheads.
Carrot seed is produced using two different methods, the “seed-to-seed” and “root-to-seed” method, depending on your goals. The seed-to-seed method is the most efficient if you have well-selected stockseed and feel confident that you can produce a genetically uniform crop without root selection. The root-to-seed method, on the other hand, affords you the chance to select the crop based on the root characteristics, replanting only the roots that meet your selection criteria, thus improving the variety. Root-to-seed also allows you to plant the root crop in a smaller nursery plot during the first season of growth and then transplant the roots to a larger field for seed production in the second season of the biennial cycle.
Seed-to-Seed Method: The vast majority of large-scale carrot seed production is done using the seed-to-seed method, which requires that the crop be sown in mid- to late summer in the field in which the seed crop will be produced the following year. The crop is left in the field throughout the winter and is able to grow and flower in situ during the next growing season until the seed is harvested the following August or September. This exposure to cold also serves to vernalize the crop, which will induce flowering the following spring. Vernalization is a cold treatment for a given number of hours below a temperature of approximately 50°F/10°C (see chapter 3, Understanding Biennial Seed Crops, “Vernalization”). In some warmer temperate areas you must make sure that there are enough vernalization hours during the course of the winter or carrots won’t fully bolt in the spring. Unless this is taken into consideration, harvesting seed from the carrots that do bolt becomes the equivalent of selecting for easier-bolting carrots, a trait that is extremely undesirable.
There are at least two main challenges to the use of the seed-to-seed method. First of all, the carrots must be overwintered without excessive damage from freezing or rodents. One of the main reasons for sowing the crop as late as mid- to late summer is so the carrots won’t be too large to go through the winter successfully. Experience has shown that carrot roots with a diameter of approximately 0.75 in (2 cm) or less at the shoulder survive winterkill due to cold temperatures better than full-sized carrots. It is generally agreed that carrots at this size can withstand temperatures at or slightly below 14°F (–10°C) if there isn’t excessive freezing and thawing throughout the winter. Though it should be noted that there are varietal differences in the ability to withstand winter conditions among carrots, with subtropical types being especially sensitive to these low temperatures.
Some growers will mechanically throw a layer of soil (“soil mulch”) onto the row in fall for winter protection, although this may hinder regrowth in the spring and promote rotting in the crown. On a smaller scale, some growers have mulched the crop with straw or other organic materials. However, in some cases this has contributed greatly to the second challenge of overwintering carrots (or other biennial roots). The mulch can create a welcoming environment for rodents to build nests amid an ample winter food supply, and you won’t know your losses until you uncover the roots in spring. Also, the mulch needs to be removed promptly in spring so as not to promote rot.
Carrot flowers in the field.
In terms of varietal integrity the main drawback with the seed-to-seed method is not being able to evaluate and select the roots that will make seed. Many of the open-pollinated carrot varieties that are available are of poor varietal uniformity due to the lack of selection through numerous generations of seed-to-seed production. If you’re going to use the seed-to-seed method, it is imperative that you use well-selected stockseed for each crop you plant. Otherwise, the “garbage in–garbage out” rule applies.
The result of using less-than-ideal planting stock will often be an amplification of any genetic flaws inherent in the population. This is because flawed roots are often less refined (hairy roots, large crowns, or outcrosses with hybrid vigor) and often make bigger flowering plants that produce proportionately more pollen and seed than the average carrot in the population. This is why open-pollinated varieties among the cross-pollinated crops are so easily run into the ground when selection isn’t practiced.
Root-to-Seed Method: The root-to-seed method requires that the carrot roots be lifted, selected, and either replanted soon after the selection process or stored in a cooler or root cellar and replanted the following spring. The advantage of this method is that it affords the grower a chance to evaluate each root and decide if it is worthy of contributing to the next generation. You must make sure that all the roots you retain: (1) receive adequate vernalization hours in storage in order to bolt the following season; (2) conform to the standards set by the selection criteria; and (3) are free of growth cracks, splits, disease, or any insect tunnels or damage. It is important to remember the old adage “one rotten apple spoils the whole barrel,” as rot in stored root crops can work much the same way.
The root-to-seed method has several modifications depending upon the climate and goals of the seed grower. If your situation necessitates replanting the roots immediately after lifting and selection (thus overwintering them in the field), then it is best to grow roots of a comparable size to the seed-to-seed method. This is especially true in areas where the winter lows approach a temperature of 15°F (–9°C), where even smaller-diameter carrots are damaged by the cold. But if you are going to store the roots throughout the winter months or if you’re replanting in a mild-winter location (temperatures not dropping below about 29°F/–1.7°C), then you may want to grow the carrots to the size in which they are normally harvested for eating. The great advantage of this is that you can then select the carrot traits at precisely the point in their life cycle that corresponds to their true use. Many carrot varieties used on the organic market are larger-rooted types like Nantes, Chantenay, Flakkee, and Kuroda that don’t fully attain their distinctive shape until they are mature. Maturity is measured by the extent to which their tip—the point from which the taproot emanates—has filled and their tips appear blunt. This blunting, as carrot breeders refer to it, along with the overall size and taper of the root, determines the characteristic shape of each carrot type. Hence, using the root-to-seed method and selecting at full size and tip fill for each variety is ultimately the only way to maintain good shape in a carrot variety. Other traits that are best selected for at full maturity include color, bolt tolerance, foliar disease tolerance, and very importantly flavor. (See “Maintenance and Selection of Genetic Stocks.”)
Cold Storage of Roots: Proper storage of carrot roots for the root-to-seed method is very important, as some growers may need to store the roots for upward of 5 months before replanting in the spring. Roots of biennial crops such as carrots that are stored for seed production are known as stecklings. Environmental conditions for carrot stecklings stored for seed production are essentially the same as for carrots stored for consumption. The storage temperature should be between 35 and 38°F (1.7 to 3°C) to slow the roots’ physiological processes, but avoiding freezing with errant temperature swings when the cooler is set closer to 32°C (0°C). This exposure to cold temperatures must be for at least 8 weeks in order to fully vernalize the roots and promote flowering and subsequent seed production in most carrot varieties (see chapter 3, Understanding Biennial Seed Crops, “Vernalization”).
Carrot roots must also be stored at a high relative humidity of about 90 to 95% to remain in good condition for subsequent growth when replanted. These two environmental requirements—temperature and relative humidity (RH)—are most easily satisfied with a cooler with humidity control. If you’re using this type of cooler, you can store clean, sound stecklings in wooden totes with small openings between the slotted planks on the sides to allow the free flow of humidity to reach the roots. At the Alf Christianson Seed Company I found that covering these totes with a 2- to 3-in (5- to 7.6-cm) layer of clean wood shavings (not sawdust!) will keep the roots free of standing water that can accumulate on the surface of the uppermost roots under high-humidity conditions. This helps eliminate a source of potential rot. Cedar wood shavings may be superior for this purpose, as cedar is reported to have a higher level of antimicrobial factors than most other woods.
Carrot stecklings can also be stored in traditional root cellars, which benefit from cold temperatures and high humidity of the earth or soil at varying depths in many temperate zones. In root cellars carrot roots or stecklings are traditionally stored in moist, clean sand or clean, undecayed deciduous leaves (in New England people swear by oak leaves, which have relatively lower tannins), where the roots are laid carefully between layers of this material so as not to touch. This can slow the spread of rot through the lot of roots. It is crucial that you wait until the temperature of the cellar is about 40°F (4°C) or below for proper storage, which will also ensure a higher humidity.
Alternatively, stecklings can be placed into plastic bags that will create a high-humidity environment for the roots. Make sure that there is a series of small penny-sized holes (three to four rows of six to eight holes for an 18 × 36 in/0.5 × 1 m bag used for 25 lbs/11 kg of carrots). Into each bag put three large handfuls of wood shavings, trying to spread them evenly among the carrots. These shavings will soak up much of the condensation that forms, and the holes will allow for excess moisture to slowly escape from the bags. Care should always be taken not to place warm roots from the field into any of these various cold storage situations directly, as this will cause excessive condensation that may promote rot.
Preparation of Stecklings for Storage: Special care should be given to stecklings of all biennial root crops prepared for storage. Carrots must be cleaned gently of all soil clinging to the roots without the use of water. This is best achieved by harvesting the roots during clear, dry weather, preferably when the soil has had a chance to dry to the point where it readily crumbles and falls away from any root surface. Don’t use a hard brush and avoid rubbing any soil vigorously against the surface of the root; stiff bristles, or any sand or small rocks in the soil may abrade and damage the surface of the carrot, thus allowing an avenue for fungal or bacterial infection during the long storage period. Never wash the roots and avoid getting them wet in any way before storage, as this will only encourage the growth of rots. If roots do get wet due to unanticipated rain, let them air dry thoroughly. This can take several hours, so if the stecklings are small they will need to be checked frequently so that they do not become too dry. Healthy soil has many beneficial microbes that will discourage the growth of root rot under most conditions; therefore we do not need to be concerned with getting all the soil off before storing the stecklings.
Proper removal of the tops from carrot stecklings is very important for long-term storage. The leaves and petioles (stems holding the leaves) are collectively called the tops and are often the most susceptible part of a carrot plant to rot. Removing as much of the tops without destroying the growing point within the crown is crucial to your success in storing stecklings of any root crop (see chapter 3, Understanding Biennial Seed Crops, “Preparing Roots for Storage”). For the 8- to 10-week storage period before transplanting (which is often used primarily to vernalize the crop) the tops are literally twisted at about 1.5 to 2 in (4 to 5 cm) above the crown, which tears the petioles but doesn’t usually promote significant rot in this shorter storage time. However, if you are going to store the stecklings throughout the winter, which can be for upward of 5 to 6 months, then you should trim much more of this easily decaying tissue. Trimming will require a sharp knife, a steady hand, and a little bit of knowledge of where the new top growth will come from when the steckling is transplanted. All new shoot growth upon replanting emanates from the crown or the stem apex. This is the point where the petioles connect to the carrot and the shoot apical meristem creates all new foliar growth. It is possible to trim most of the petioles off, about 0.25 to 0.33 in (0.6 to 0.8 cm) above the crown, and not damage the growing point (hence not hindering subsequent leaf and flower stalk development). You should then be able to see very small fern-like leaves below the point where you have cut and not see the round outline of an orange-white stem. If you see the outline of a stem, either you have cut too close or that particular root has already started flowering and you have cut off the emerging flower stalk. It is a good idea to practice this technique on roots that you don’t intend to use for seed production until you get the hang of it.
Planting: Initial sowing/planting for the seed-to-seed or root-to-seed method should only be done into well-prepared soil with good moisture-holding capacity, just as you would for the vegetable crop. As the crop will be planted in summer in most locations you will need to ensure even, adequate moisture to achieve a good stand. In desert production of carrot roots in California, where seeding is frequently done in late summer at temperatures around 100°F (38°C), growers use daily overhead irrigation for evaporative cooling in the top horizon of the soil until germination and emergence are achieved.
For the seed-to-seed method, seed is sown sparingly so that only a cursory thinning is necessary to achieve the desired in-row spacing. Thinning can be achieved by blocking with a hoe or by cross-cultivating with a spring-tooth harrow or tine weeder across the field at a perpendicular angle to the rows of carrots when they are young but well-established seedlings. The goal is to achieve an in-row spacing between roots of 4 to 8 in (10 to 20 cm). The spacing between rows can be from 22 to 36 in (56 to 91 cm). Many growers have gone to the closer row spacing of 22 in (around 55 cm) for seed-to-seed production in recent years.
With the root-to-seed method carrots are sown much as a grower would for producing the vegetable. As the crop is planted in midsummer, you should be particularly careful to plant at a spacing that will ensure that roots achieve their optimum characteristic size and shape for selection upon lifting in the fall. Upon replanting stecklings in the spring the in-row spacing should be 8 to 12 in (20 to 30 cm) between plants, as fully grown stecklings often produce larger plants. The spacing between rows is routinely between 24 and 36 in (61 to 91 cm).
The spacing between plants within the row is partly dependent on the type of carrot you’re producing. If you are producing seed of Amsterdams, Paris Market types, or true Nantes types (or inbred lines for hybrid production) it is possible to plant them at a closer spacing, as they all have flowering plants that are of a smaller statue than most other carrots. These types are frequently planted 4 in (10 cm) apart within the row for the seed-to-seed method and 8 in (20 cm) apart for the root-to-seed method. Other types of carrots, like Imperators, Chantenays, Flakkees, or Kurodas, usually have larger frames and are planted at 8- to 12-in (20- to 30-cm) spacing, respectively, for the two methods.
The density of the planting also influences which class of umbel yields the highest proportion of seed. The carrot seed produced by the primary and secondary umbels is universally regarded as superior to later-forming seed of the third- and fourth-order umbels, due to its size and degree of maturity. In many temperate regions third- and fourth-order umbels commonly have a large percentage of their seed that is small, hasn’t fully matured, and has a lower germination rate. Under higher-density plantings the development of the later-forming third- and fourth-order umbels is restricted, thereby benefiting the development and quality of seed from the primary and secondary umbels.
Transplanting: Carrot stecklings are usually prepared for replanting in two steps. First the tops should be removed at harvest (see “Preparation of Stecklings for Storage”). This cuts the transpiration flow from the plant and preserves moisture in the root. Upon transplanting the steckling, the carrot will regrow new foliage soon after reestablishing new feeder or adventitious roots. The next preparatory step is to cut about one-third of the root off at the bottom or taproot end of the carrot. This gives you a chance to see both the intensity of the color of the carrot and the size and color of the core for selection purposes (see “Maintenance and Selection of Genetic Stocks”). The cut should be made cleanly, with a sharp knife, and at a slight angle laterally (15 to 30 degrees from a straight diagonal cut). This allows for quicker healing of the wound, and the root will meet with less resistance when it is pressed into the soil upon transplanting. These cut roots are then placed, one deep, in a cool, airy area for several hours to allow the wound to heal or suberize, forming a scar-like protective layer on the cut surface. Stecklings must be at least 3 to 4 in (8 to 10 cm) long to successfully regrow and are often 6 to 8 in (15 to 20 cm) long. This length easily accommodates replanting into furrows as compared with full-sized carrots.
Carrots are insect-pollinated and, like most crops in the Apiaceae, are very attractive to a wide diversity of pollinators. This is relevant as carrots grown for seed in most temperate-climate settings will attract insects from a broad perimeter around the field in which they are planted. However, this also means that you will need to be careful in determining isolation distances from other carrot crops and any wild carrot (Queen Anne’s lace) that may be present in your region.
The standard isolation distance of 1 mi (1.6 km) between carrot crops of the same crop type, without physical barriers on the landscape, should be observed (see chapter 13, Isolation Distances for Maintaining Varietal Integrity, for a full discussion of physical barriers). In cases where significant barriers dot the landscape it is possible to diminish this distance to 0.5 mi (0.8 km). Crop types in carrots would include Nantes, Imperators, and Chantenays; each of the unusually colored carrot types (purples, reds, yellows, and whites) would constitute a major group. As it is always possible to have some crossing at these distances, two carrot varieties within a particular group will suffer less varietal damage if crossed than if a Chantenay were crossed with an Imperator in the production of commercial seed.
If you are producing carrot seed of a different type than the nearest neighboring carrot seed field or a known patch of wild carrot (Queen Anne’s lace), you will have to double the distance to ensure a high level of genetic purity. Between different carrot types you will need 1 mi of isolation with barriers and 2 mi (3.2 km) without barriers. This is important to observe across the different color classes and also serves as the minimum distances to be used for any carrot stockseed production (see chapter 17, Stockseed Basics).
Harvesting high-quality carrot stockseed by hand.
Maintenance and Selection
of Genetic Stocks
Maintaining the genetic integrity of open-pollinated carrot varieties that are good performers requires attention to detail, knowledge of carrot traits, and a higher level of commitment than for many other vegetables. As with many cross-pollinated species, even well-selected carrot varieties with a high degree of uniformity are genetically heterogeneous and may have an appreciable amount of variation in the traits you’re selecting. Remember that when selecting a crosser like carrots your goal is to establish the amount of variation that is acceptable for each trait of interest and not select so narrowly that you jeopardize the genetic integrity of the variety. Carrots are more prone to inbreeding depression than most cross-pollinated crops. Many a good carrot variety has been ruined by an overzealous person selecting a relatively small number of “perfect” roots for a seed increase and thereby narrowing a genetically healthy carrot population (variety) into a shadow of its former self. The health and genetic resiliency of a good carrot variety relies on keeping a broad genetic base. The art of the selection process is having an appreciation of the breadth of variation for the traits of interest that can be retained while still producing a variety that is uniform enough to satisfy the farmers who will produce the crop and the markets they serve.
Selection for Foliar Characteristics: Selection in carrots begins before the roots are lifted. As with all root crops, carrot tops are an important constituent of the crop, especially for the organic grower. Selection for vigorous seedling growth and the early establishment of a robust full set of leaves can be instrumental in developing a carrot for the organic market that is able to compete with weeds early in the season. Selection for this foliar canopy that will better compete with weeds can be done early in the season, long before the roots are fully formed. Also important is the stature of the carrot’s foliage. Selection for carrot tops that stand erect with minimal contact with the soil is important in slowing the potential spread of both fungal and bacterial foliar diseases that are soilborne. Foliar diseases can decrease the yield and eating quality of the carrot root crop by diminishing the amount of energy (and sugars) that is fixed through photosynthesis. They can also severely affect the yield and quality of the seed crop (see chapter 16, Seedborne Diseases).
If foliar diseases are present when producing the carrot roots for seed production it is often possible to select for horizontal resistance to these pathogens. When present, there is usually a continuum of disease symptoms that can be observed from plant to plant within the crop. In this situation it is advisable to rogue out (eliminate from the population) the most susceptible individuals. This can be done as early as symptoms arise to slow the spread of the pathogen and can be repeated throughout the season, including during the flowering cycle in Year 2.
Selection for Root Characteristics: With the root-to-seed method of seed production you will have a golden opportunity to select for many root characteristics. There are as many and varied a number of root characters to select for as there are colorful characters who grow carrot seed in this world. I will list the most important traits that are universally selected for, realizing that for any particular carrot type or carrot variety there may be traits of import for that specific type or the market it serves.
Nash Huber and Micaela Colley evaluating and selecting for root characteristics in a carrot trial in Sequim, Washington.
The shape of a carrot variety is probably the most recognizable feature of that carrot. As stated earlier, the shape, relative size, degree of taper, and extent of blunting of the tip determine the characteristic shape of each carrot variety. While the environment exerts a sizable amount of influence on these traits, the seed grower must make the overall shape of the roots a top priority in the selection process, as the shape of a carrot variety will become much too variable in very few generations if ignored. Another trait that is usually quite variable is the degree of smoothness of the surface of the root. The predominant features on the exterior of a carrot root are the lateral root scars that appear as pale, off-white lines in small indented regions running perpendicular to the length of the root. Selection for small lateral root scars with a minimum of indenting will make the carrot appear smoother. It is also important to select against the presence of small adventitious roots that occasionally emanate from these root scars.
Carrot roots are very prone to producing additional lateral roots, a tendency growers call forking. Sometimes this forking will result in as many as three, four, and even five additional lateral roots. There is a lively debate among researchers as to whether these extra roots are due to early damage of the developing taproot from either a root rot organism or a nematode feeding, from hardpan or hitting a rock. Regardless of the cause, the consensus among carrot breeders is that the genetic background of a carrot can influence the degree of forking in a particular variety; hence it is possible to select against forking. Also common in carrots is the propensity of certain carrots to crack while growing and then fully heal. These growth cracks result in ugly scars in the mature crop that make the carrot unmarketable. Alternatively shatter cracks may occur at the time of harvest from any impact sustained by the root during the harvesting process. They appear as long, vertical cracks along the length of the root and also make the affected roots unmarketable. While both types of cracking are thought to occur due to excessive uptake of water, it is agreed that genetic selection against both forms of cracking over time can lessen the extent of the problem.
Breeding for color in carrots is a time-honored tradition, as described in the development of orange carrots. When the intensity of the color in a variety is relatively low, as it is with older orange varieties and in most of the open-pollinated unusually colored carrots, then it is possible to select based on a visual inspection of the exterior of the root. For improved accuracy in selecting for root color, however, it is important to make a smooth lateral cut and visually evaluate the internal color (as described in “Preparation of Stecklings for Storage”) to more accurately compare the intensity of color between roots. This is a highly heritable trait that will improve rather quickly through several cycles of selection. The added bonus is that all of the carrot pigments are nutritionally significant, and these increases represent a health benefit to anyone eating the variety!
Selection for flavor is very important; we all know how many bad-tasting carrots there are in this world. However, selecting for carrot flavor isn’t easy, for a couple of reasons. First, it requires tasting each root in the carrot population you’re reproducing. This is usually done with smaller breeding populations of 300 to 400 roots (see chapter 13, “Cross-Pollinated Crops”) that are grown using the root-to-seed method, where it’s possible to taste the piece that’s cut from each root in preparation of the stecklings. (You quickly learn to spit out each bite that you taste to avoid the stomachache that can come from over 300 bites of carrot.) Second, carrot flavor is biochemically quite complex, and there is no consensus among carrot lovers on what constitutes the ideal. Many people want the sweetest, mildest-flavored carrots, while others prefer a strong “carroty” flavor that isn’t too sweet. And the genetics for human ability to discern flavors is also quite variable. So all those selecting for carrot flavor must be confident in their own ability to assess the relative merits of a particular carrot.
Celery & Celeriac
The domestication story of Apium graveolens L., which includes celery, celeriac, and the ancestral type, smallage, is incomplete, but it is undoubtedly the result of selection by several agricultural societies living between the eastern Mediterranean and the Himalayan foothills. Originally marsh species, wild forms of these crops are still found in wetlands throughout the warmer temperate zones of Europe and western Asia. The earliest use of this species was for the medicinal properties of its seed in ancient Egypt and in the Roman Empire. The seed and seed extracts were used as a diuretic, for intestinal ailments, and as an aphrodisiac. As a vegetable the earliest domesticated version of celery and its allies was probably a leafy plant with smaller, non-succulent stems, not unlike smallage, or leaf celery, which is still cultivated widely across Asia and is used primarily as a salad green, potherb, and aromatic herb in cooked dishes.
The development of celery as the crop that we know in the modern era probably started in Italy and France beginning in the 16th century. The most important traits that were selected by farmer-breeders in transforming the crop at this time were increased fleshiness of the petioles (leaf stems) and reduced levels of strong or aromatic compounds; these developments would redefine the use of this vegetable. As these petioles or stalks became the primary part of the plant used in this European version of the crop, celery began to spread across Europe and beyond, becoming a prominent vegetable in many temperate areas of the world. Celeriac or celery root appeared in European agriculture sometime in the 17th century as an apparent variant of stalk celery, eventually becoming important for its role as a winter storage crop in many of the colder reaches of Europe.
‘Redventure’ is an open-pollinated red celery from Wild Garden Seeds in Philomath, Oregon. For seed production it is important to select against the open habit exhibited by this plant.
Celery is not as cold-hardy as many of the other Apiaceae seed crops and is therefore grown in temperate regions with milder winters than many crops in this family. Much of the commercial celery seed crop is grown in the coastal valleys of California near San Luis Obispo and the warmer reaches of the Rhône River Valley of France. Celeriac seed is also produced in these areas, and there is a significant amount of localized production still done in Eastern Europe, where the crop is a staple vegetable that is used daily in many areas as a soup or stew ingredient. Seed of smallage and the many other variants of leaf celery are still grown on-farm in almost all of the agricultural areas from the Mediterranean to eastern Asia, where these crops are essential to the regional cuisine as vegetables and as aromatic condiments and where they are more extensively cultivated than celery. Because leaf celeries are more heat-tolerant than other crops in this species, their seed can be produced throughout a much wider climatic area than stalk celery or celeriac.
Crop Characteristics
Reproductive Biology
Celery is a biennial that sequesters most of the stored energy from its first season of growth in its petioles or stems. Therefore, to successfully produce an acceptable yield in the seed crop, you must produce a plant in the first season of adequate size and stored food to produce a robust flowering plant in the second season. If allowed to grow to its full size where it is sown it will produce a sizable taproot as well; however, if the first-year plant is grown in a nursery and transplanted using the equivalent of the root-to-seed method (see chapter 6, Carrot, “Root-to-Seed Method”), then the long taproot will be severed in transplanting. Celeriac produces a more traditional biennial taproot and is better suited to the root-to-seed method.
A flowering celery plant.
After vernalization and flower initiation the celery plant grows to a height of 3 to 4 ft (0.9 to 1.2 m) during the second season of growth. Celery and its allies produce a highly branched plant that contains a series of compound umbels. These umbels are smaller and considerably less compact than the umbels of carrots and most other commercial Apiaceae crops. The flowers are white and usually shed pollen in the morning soon after the petals open for the first time. After 3 to 5 days the style becomes fully extended and the stigma becomes receptive, therefore encouraging cross-pollination. Celery and its allies, however, do not have any barriers to self-pollination and will produce a certain amount of selfed seed, based on insect movement from one umbel to another. Celery produces abundant nectar, and many species of insects, including wasps, syrphid flies, and bees, take part in the pollination. The seed that is produced, like that of the carrot, is borne in pairs and results when the schizocarp fruit splits at maturity.
The compound umbels of the celery inflorescence.
Climatic and
Geographic Suitability
Commercially produced celery seed is grown in milder winter regions than many other Apiaceae seed crops, when it is overwintered using the seed-to-seed method. Celery is more tender than most of the biennials in this family. Many stalk celery varieties will survive frosts from 28 to 32°F (–2 to 0°C) if they are hardened off gradually but will suffer severe damage at lower temperatures, which restricts the temperate regions where seed can be grown. Celeriac and leaf celery can usually withstand temperatures that are slightly colder, but they are also more easily damaged than many other species in this family. You can use floating row covers to protect all of these crops from light frost, but experiment with them with before relying on them to protect the plants below 30°F (–1°C).
The celery seed crop must be grown in temperate zones that have regular intervals of cold temperatures between 40 and 50°F (4 to 10°C) during the winter months between the seasons in order to be fully vernalized. If celery plants are stored in a coldroom between seasons, they will need temperatures in this range (or colder) for several weeks before they can be transplanted and expected to bolt. As with most biennials the duration and temperature range needed to promote flowering vary greatly among varieties, and you must have good observational skills to determine if the variety is receiving adequate vernalization for the entire population to bolt and produce seed.
Seed Production Practices
Soil and Fertility Requirements
Celery and its allies were domesticated from wild marsh plants that grew in the peat soils in and around the Mediterranean. The modern crop still thrives in organic soils and loams with a high percentage of organic matter, though a wider range of fertile soils can be used for the seed crop. Growing a successful crop has always demanded relatively high levels of macronutrients and a steady source of moisture throughout the season. Nitrogen levels for the seed crop should be carefully monitored, as excessive amounts of N can be problematic in producing a flowering celery crop. Celery also requires a relatively high pH, between 6.5 and 7.5.
Growing the Seed Crop
Seed-to-Seed Method: Commercial celery seed production is usually done using the seed-to-seed method in a similar fashion to its use for root crops like carrots or beets (see chapter 6, Carrot, “Seed-to-Seed Method”).
The crop is direct-seeded or transplanted as seedlings in mid- to late summer of the first growing season into the field where the plants will stay through the end of seed production. Celery has been traditionally planted on 3 ft (0.9 m) centers for seed production, though some growers now plant as close as 2 ft (0.6 m) between rows. The final in-row spacing between plants can be from 1.5 to 2 ft (0.5 to 0.6 m). When using the seed-to-seed method the in-row spacing between plants can be much closer than this through the early stages of growth, as this will afford you several stages to perform phenotypic selection before it is necessary to settle on the final population at the appropriate spacing as the crop begins to flower in the second season.
Root-to-Seed Method: When using the equivalent of the root-to-seed method (the plant-to-seed method in the case of stalk or leaf celery), you can either direct-seed or transplant seedlings into a high-density nursery or produce the plants as you would the vegetable crop. The crop is planted in midsummer (early summer if you want to grow them to full vegetable “maturity” for selection purposes). If the climate is mild enough then the plants can either remain in a nursery until spring before transplanting or they can be transplanted in the fall into the seed production field. In either of these cases they can be transplanted into the final spacing given for the seed-to-seed method.
Alternatively, if your climate experiences winter lows below the 28 to 32°F (–2 to 0°C) range, you will need to lift and select the plants in the fall and place them in cold storage until you transplant them the following spring in the seed production field. Storing stalk and leaf celery is somewhat different from storing the Apiaceae root crops. Storing celeriac is done in a similar fashion to storing carrots or parsnips. However, for celery and leaf celery you should leave much of the soil that clings to the roots upon lifting the plants, as the plants’ roots need to stay buried in moist soil for the duration of the storage period. The temperature in the coldroom should be maintained as close to 34°F (1°C) as possible. The relative humidity of the room should be close to 75% if possible, as humidity is necessary to keep the petioles and foliage from desiccating. If the humidity goes above this level, though, it can cause freestanding water to form on the plants’ surfaces, which can promote rot. As with all coldrooms there should be good ventilation; air movement in the vicinity of the plants is very important, as plants will probably be packed together tightly and need the flow of air to avoid decay.
The duration of the storage period needed to initiate vernalization does vary greatly for the different varieties of celery and its allies, but most growers working with these crops agree that a period of at least 8 to 10 weeks of cold treatment is necessary to fully vernalize the entire population. Celeriac may require at least 2 to 4 more weeks of cold than the other celeries to become fully vernalized, as it is a colder-season version of these crops; it has been selected for longer-term storage to fit the more northern growing regions and has become adapted to these colder growing seasons.
At the end of the storage period all of the propagules of the celery allies must be checked for decay and viable apical growth when you sort them before transplanting. Outer celery stalks that have decay can be eliminated, as should any vegetation that has desiccated or gotten too leggy. Any pruning that is done at this time should take into account that the apical growing tip must be left fully intact to expand into the flowering plant.
Seed Harvest
Seed harvest for celery and its allies is similar to other Apiaceae crops. Celery plants are pulled or cut right at ground level when the variety has matured a majority of the seed on most of the plants. A majority of the seedheads will have a brownish cast, and the plants will turn yellow as they senesce. As with all Apiaceae crops there is a delicate balance between waiting for a majority of the seed to mature and losing some of the earliest-maturing seed present on any given plant during this wait due to shattering. Celery seems to be more prone to shattering than carrots; therefore keeping close vigil when observing celery seed maturation is important. As with all dry-seeded crops, the timing of harvest and dry-weather cycles is part of what distinguishes good seed growers from the rest.
Because celery seed may shatter more readily than the seed of other related crops, there is good reason to lay mature celery plants onto landscape fabric (or some other type of permeable cloth that will allow water to drain through it in case of precipitation) when making windrows. Windrowed plants should be allowed to dry for at least 4 to 7 days, being turned once during the drying process. The crop needs to be monitored closely and threshed through a stationary thresher or fed through a combine before significant shattering takes place. These processes are always best done in midmorning after the dew has lifted but while the stems are still pliable.
Genetic Maintenance
Because the celery seed crop is often planted at a later time in the season than the vegetable crop would be planted, it is important to do initial selection on the crop when you grow it to full maturity as a vegetable crop. By doing this it is easier to select for all of the traits associated with the fully grown petioles (stalks) and determine which plants have the desired traits for the cultural and market conditions under which they will be grown. Traits include height, color, petiole size and ribbiness, stem base, flavor, texture, and resistance to diseases or insect pests. The height, stature, and leafiness of the plants are important, and the overall plant should appear symmetrical and cylindrical. The color of the stalks should be uniform. Selection is for either the light green or yellowish self-blanching types or the greener types that are favored in North America. Selection for size, shape, and tightness of the stalks around the heart is important. The stalks should also be smooth with an absence of pithiness, stringiness, and large ribs. Petiole cracking and the presence of disease should also be monitored and selected against.
The flavor variation in celery can be great as with all Apiaceae crops, though many modern plant breeders ignore flavor in their selection, assuming that all celery is bland and basically tastes alike. On the contrary, most chefs consider celery an important flavorful aromatic, and indeed, once you start to taste the different varieties and familiarize yourself with the differences that exist in the distinctive celery flavor, it will be easy to select for flavor within an open-pollinated variety or segregating population.
Celeriac is often grown to its full size as a vegetable and stored over winter in a root cellar to be transplanted for the seed crop in many parts of the world. This is possible because celeriac stores so well. The roots are stored and transplanted in a similar fashion to carrots (see Carrots, “Cold Storage of Roots” and “Planting and Transplanting”), however the roots themselves do not require cutting before transplanting them. Growing the crop to full edible root maturity allows you to select for root characteristics such as size, shape, root smoothness, crown size, and the amount and extent of secondary roots. Foliar characteristics like height, width of petiole, attitude, and color are often also selected for in the first season before lifting the crop for storage or transplanting. As with all biennials it is important to eliminate any plants that show any sign of bolting in the first season, as well as any plants that bolt so late in the second season that they are unable to mature seed in a timely fashion. As always, unhealthy or malformed flowering plants should be eliminated at any stage throughout the second season.
Isolation Distances
The standard isolation distance of 1 mi (1.6 km) should be used between celery crops of the same type when there are no physical landscape barriers between two seed crops. In cases where there are significant barriers it is possible to reduce this distance to a minimum of 0.5 mi (0.8 km). As it is always possible to have some crossing at these distances, two celery varieties of the same type will suffer less varietal damage if crossed in the production of a commercial seed crop. Celery types can be categorized into classes by height, time of maturity, and whether the variety has stalks that are self-blanching or green (or pink/red). If you are producing seed of a different celery type than the nearest neighboring celery crop, then you will need to double the isolation distance to a minimum of 2 mi (3.2 km) to ensure a high level of genetic purity if there are no barriers on the landscape.
This increased minimum distance of 2 mi (3.2 km) between seed crops is also very important to use if you are producing either a celeriac or a leaf celery seed crop in the same locale as a celery seed crop. When there are significant barriers on the landscape the isolation distance can be decreased to a minimum of 1 mi (1.6 km) for all of the diverse types of this species.
Cilantro
Cilantro (Coriandrum sativum) is one of the oldest known culinary herbs and is native to the Mediterranean basin. Its origins are obscured by the fact that it apparently spread through agricultural societies of the Mideast before recorded history. Seed dated to 6000 bce was recovered in a cave dwelling in modern-day Israel. Sanskrit writings refer to its use as far back as 5000 bce. It made the trip to China via the Silk Road and traveled north to Europe with Roman conquest. The herb then traveled to the Americas with the Spanish conquistadores. Its use is woven into the fabric of the cultures of North Africa, the Middle East, and Asia Minor. The herb is known as cilantro when used in the Spanish-speaking countries of North, South, and Central America; in other regions it is referred to as coriander leaf or as Chinese parsley. It is also used extensively in the cuisines of Southeast Asia, India, and China.
It is hard to determine when the leaves of cilantro were first used as an herb for flavoring, but cilantro has undoubtedly had a long culinary history and continues to serve as two distinct, very important crops worldwide. It is grown in many cultures for its very aromatic foliage, which is used as both a cooked and raw condiment. Cilantro leaves give salsa its distinctive flavor. Its seed is used as a spice, coriander, which is an important ingredient in curries, chutneys, and breads across much of the Old World. The roots are used to add an intense flavor to soups and curries in several Asian cultures. The use of cilantro has grown in recent years as many of these culinary traditions have expanded into North America and Europe.
Cilantro (Coriandrum sativum).
The great majority of the cilantro seed used across the world for planting is grown locally by farmers. There are undoubtedly thousands of varieties adapted to the unique climates and culinary needs of the people who cultivate these varied strains around the world. Large-scale commercial seed production is done in Mediterranean climates with seasonal dry weather occurring during the seed maturation stage. In North America the cool coastal valleys of Washington State produce good yields of high-quality seed.
Crop Characteristics
Reproductive Biology
Cilantro is a cross-pollinated annual that stands upright with a height of 1 to 1.5 ft (0.3 to 0.5 m) in the vegetative phase of its life and extends sometimes to a height of 3 ft (0.9 m) during flowering and seed production. Leaves of the vegetative plant transition from a trifoliate ovate shape with deep cuts on the margins to a more frilly, highly pinnate form emerging from the flower stalk that’s almost feathery in appearance. The inflorescence is a compound umbel that is typical of the Apiaceae, yet smaller than the umbels of carrots or dill. The flowers are borne on umbellettes and are asymmetrical, with longer petals on the outer side of the umbel. Cilantro is self-fertile, though as with all Apiaceae cross-pollination is the norm, with insects of many species working the flowers.
Climatic and
Geographic Suitability
The climatic requirement for cilantro seed production is essentially the same as for the other important vegetable Apiaceae. The main difference is that cilantro can mature a crop somewhat earlier and under cooler conditions than is possible with carrots or parsley. This is borne out in the seed production areas around the Salish Sea of Washington in the United States and British Columbia, Canada; parsley and carrot will not fully mature a satisfactory commercial seed crop in the cooler maritime valleys of the area, requiring warmer interior valleys to the east and south of the Salish Sea basin. In contrast, cilantro plantings in these coastal valleys do produce perfectly acceptable commercial seed crops with a high percentage of seed maturing. In fact, this cool coastal climate allows cilantro the chance to produce a larger frame (basal rosette of leaves) in spring that supports a large complement of flowers and, therefore, a better yield of seed. Another unique quality of cilantro, one that isn’t shared by many of the other cool-season crops, is its ability to produce good-quality seed in hotter climates. While it may not produce optimum yields in hotter climates, where it doesn’t put on as much spring growth before flower stalk initiation, it is still capable of producing high-quality seed. This is not surprising when you consider that much of the cilantro that has been cultivated for at least 2,000 years has grown in hot climates.
Seed Production Practices
Soil and Fertility Requirements
Cilantro seed crops will tolerate a wide range of soil types as long as adequate fertility and moisture levels are maintained. However, soils must be well drained to avoid losses from root rot organisms. Lighter soils are especially important for establishing early plantings. Cilantro can produce a good crop from moderate levels of balanced fertility. Fertility from compost, legume plow-down, or other organic sources should produce a satisfactory seed crop. Excessive foliar growth early in the season due to an overabundance of nitrogen can cause a leggy seed crop, in which plants may lodge (fall over) during seed production.
Growing the Seed Crop
It is important to plant cilantro early enough in the season to establish a good foliar frame during the cool weather of spring. This will support an optimum seed set once the plants begin to bolt. Cilantro is frost-tolerant and can be planted as soon as the ground can be worked, but to ensure good vigorous seedling growth the crop should be sown after the weather has settled. Temperatures between 50 and 85°F (10 to 29°C) provide optimum growing conditions. The main guiding principle is to produce a large full frame of foliage during the cool weather of spring before hot weather induces bolting. This is why the best-yielding cilantro crops are grown in cool-season seed-growing areas, even though the crop will produce successfully in hotter climates.
Cilantro is frequently planted in rows with 18 to 24 in (46 to 61 cm) centers. As plants rarely exceed a height of 18 to 24 in (46 to 61 cm), under optimum soil fertility regimes for seed crops it is possible to space the crop as closely as 14 in between rows. (Large commercial production is done at 22 to 24 in/56 to 60 cm row centers.) In-row spacing is usually done at 4 to 8 in (10 to 20 cm), so it is easy to eliminate any early bolters that may not be easily seen at a tighter spacing. When the seed is planted there are frequently “doubles” or two seedlings that will appear where each seed is planted. This is because the ribbed, globe-like seed of cilantro is really a two-seeded fruit. Some growers will split this schizocarp fruit by gently running the seed between rollers before planting, therefore increasing the number of single seeds planted. If this is not done the grower will often go through and thin any doubles to single plants to achieve a good plant density.
Asymmetrical cilantro flowers with longer petals on the outside of the umbel.
Seed Harvest
When a majority of the cilantro seed is mature the plants should be cut and placed in windows to cure during dry, settled weather. The timing of this is particularly critical with cilantro as discoloration of the seed can easily occur with precipitation. This discoloration is not well understood and hasn’t proven to be detrimental to the seed quality (it’s probably due to saprophytic fungi or bacteria). However, growers and seed companies perceive this discolored seed as being of poorer quality. The best way to combat this is by growing the seed under the driest conditions possible at the time of seed maturation. As with all dry-seeded vegetables, overhead irrigation should never be used during the later stages of seed production while the crop is maturing. When the plants are cut for harvest during dry weather it is a good idea to swath them in the morning while there is still dew as it will minimize the shattering of the most mature seed from the plants.
Genetic Maintenance
Selecting against early bolting is one of the most important things a seed grower can do in a fast-growing leafy vegetable crop (spinach and arugula are two other good examples). Otherwise a crop like cilantro will invariably become faster bolting over several generations due to genetic drift. More than one cilantro variety released specifically as a “slow-bolting” variety in the last decade has degraded to a significantly faster-bolting type due to a lack of selection for this trait during repeated increases of the seed crop used as stockseed.
Other traits that may be considered for selection include seedling vigor, leaf type, and upright stature. All of these can be visually selected during the normal seed production cycle. Variation for flavor is common in almost all cilantro populations. Selection for uniformity of flavor requires a discerning palate and an infinite amount of patience but has been done. Selection for improved flavor is possible if a good range of flavor variation exists in the population in question.
Isolation Distances
Cilantro requires the same standard isolation distance as other members of the Apiaceae. If grown in open terrain, isolation between seed crops should be 1 mi (1.6 km); in an area with a substantial number of barriers on the landscape the isolation can be decreased to 0.5 mi (0.8 km) (see chapter 13, Isolation Distances for Maintaining Varietal Integrity). An increase in isolation may be necessary when two cilantro crops with significantly different characteristics are grown in the same region. For instance, if one crop has a distinct type of foliage, flavor, or stature that is different from another cilantro seed crop that will be grown nearby, then the isolation distance should be increased to 2 mi (3.2 km) in open terrain or 1 mi (1.6 km) with substantial barriers. This increased isolation distance might be especially necessary if one field is a fast-bolting coriander type grown for its aromatic seed and the second field has a slower-bolting, leafy cilantro type.
A real threat from unwanted cross-pollination also exists if there are any diversified vegetable farms or home gardens with cilantro growing in the vicinity of any commercial seed crops. This is because a portion of almost any cilantro grown as a leaf crop will invariably bolt and flower before it is turned under.
Parsley
Parsley (Petroselinum crispum) originated in and around the Mediterranean basin and was grown by the Greeks and Romans more than 2,000 years ago. It was originally cultivated for its medicinal properties, being used to improve digestion and increase assimilation of food. It also served as an important remedy for ailments of the bladder and kidneys, and its efficacy for the health of these organs has been borne out by modern scientific investigation. It is unclear when parsley was first used as a vegetable and herb, but it appears that its culinary importance grew as its use spread geographically.
By the 15th century parsley was being grown extensively in Western Europe; from there it spread to many parts of the world over the next three centuries. During its domestication, selection centered upon profuse leaf development and increased volatile flavor compounds that have made it the popular herb it is today. Human selection also produced various forms of the crop based on the degree of curling of the leaves, from the flat Italian types (P. crispum var. neapolitanum) preferred by many chefs to the double, triple, and moss curled types that are of greater economic importance in Northern Europe and North America. A form of the crop (P. crispum var. tuberosum) has also been developed for its fleshy taproot and is known as Hamburg parsley or turnip-rooted parsley. It is used like any other root vegetable, and is a staple ingredient in soups and stews in parts of Northern and Eastern Europe.
Italian flat leaf parsley (Petroselinum crispum var. neapolitanum).
Both as a foliage and root vegetable parsley is grown as an annual, planted anytime from early spring through midsummer depending on the climate or seasonal harvest needs. Once the crop enters its reproductive phase in the second year of the biennial cycle, the quality of its leaves or roots for food is greatly diminished.
Commercial parsley seed is grown in many of the same areas that have traditionally been important in the production of carrot and parsnip seed, including the Rhône River Valley of France, the Sacramento Valley of California, and the agricultural valleys of central Oregon and eastern Washington. Parsley seed is also grown regionally by smaller producers in most of the cultures of Eastern Europe and western Asia, where this crop is used extensively in their cuisine. Hamburg parsley seed is also grown as a commercial crop in all of the major production areas to a limited degree, but the majority of cropping is done on a more localized scale in or near the areas of intensive demand.
Crop Characteristics
Reproductive Biology
Parsley is a biennial, producing a prolific rosette of leaves in the first season before vernalization promotes flower initiation in the second season. Seed stalks are usually 3 to 5 ft (0.9 to 1.5 m) tall and bear compound umbels that are less dense than most other Apiaceae crops. Each bisexual parsley floret has five pale yellowish green petals with five stamens, two styles, and a two-celled ovary. When normally fertilized the two-celled ovary produces two seeds. While parsley flowers are less showy than carrots or cilantro they appear to get just as much activity from wild insect pollinators, especially wasp and hoverfly species.
Seed set is predominantly from cross-pollination, though the crop is self-fertile. Crossing is encouraged, as stamens will usually ripen and shed viable pollen before the style of the same floret fully elongates and its stigma becomes receptive.
Climatic and
Geographic Suitability
Parsley is a cool-season crop that thrives at temperatures between 50 and 61°F (10 to 16°C) during the vegetative stage of its life cycle, though it can tolerate temperatures considerably higher than this once it is established. When grown as a seed crop parsley is probably similar to carrot in requiring temperatures above 68°F (20°C) for good flowering and seed set. Average temperatures at or above 80°F (27°C) seem to be best for maturing high-quality seed late in the season. Parsley seed is slow to mature and requires a longer season and more heat units than many of the other Apiaceae seed crops. This is why it’s often grown in the warmer reaches of the seed production climates of these crops. In North America this includes the Willamette Valley and Madras area of Oregon, both of which usually have sustained warmer temperatures at the end of the season when compared with the Apiaceae production areas of British Columbia and Washington.
Seed Production Practices
Soil and Fertility Requirements
All Apiaceae crops respond well to light soils with good tilth, similar to the soil favored by carrots or parsnips. Parsley can be grown successfully across a broader range of soil types, however, as long as good drainage, tilth, and fertility are assured. Parsley seed is slow to germinate and requires a soil that doesn’t easily form a crust to ensure a good stand. Both regular and Hamburg parsley have a substantial taproot that thrives in well-drained, healthy soils. Balanced fertility without excessive nitrogen is important in growing a solid frame to support seed production without too much foliar growth.
Growing the Seed Crop
The parsley seed crop can be grown using either the seed-to-seed or the root-to-seed methods in a similar fashion to carrots (see chapter 6, Carrot, “Seed-to-Seed Method” on and “Root-to-Seed Method”). Both of these methods require planting the crop in midsummer to ensure the production of a large enough plant to properly evaluate in the vegetative state. For the seed-to-seed method the crop is usually sown in mid- to late summer, while the crop that is grown using the root-to-seed method is usually planted before the summer solstice as its growth is delayed when it is lifted, evaluated, and transplanted in the fall. The crop must be sown into a fine seedbed that is well drained but is easily kept moist during warm weather; parsley can take up to 2 weeks to germinate and emerge.
Seed-to-Seed Method: In the seed-to-seed method the crop is sown in rows that are spaced 22 to 36 in (56 to 90 cm) apart; plants within the row are ultimately thinned to a spacing that can be anywhere from 10 to 14 in (25 to 36 cm) apart. This method works exceptionally well with all types of leaf parsley that can be adequately selected for horticulturally important traits via selection of foliar characteristics. Selection can be done over time during the first season as the leaf characters become apparent while the plant matures. Selection can also be done after the overwintering period when the plants that have less winter damage and better spring growth can be favored while eliminating any poorly performing plants.
Root-to-Seed Method: The crop can be sown in nursery beds with rows spaced 14 to 18 in (36 to 46 cm) apart with plants thinned to 1.5 to 2 in (4 to 5 cm) apart in the rows in preparation for transplanting using the root-to-seed method. Nursery beds planted at this density will easily produce enough plants to transplant into an area 10 to 15 times larger than the nursery and still give you an opportunity to select for leaf characteristics before the plants are pulled to transplant in the fall, or the following spring depending on your needs. When the plants are pulled and sorted, a selection for vigorous, disease-free roots is also possible and should be practiced with all types of parsley. For Hamburg or root parsley, selection for solitary, nicely formed roots with little or no branching is advised. All selected plants should have most, if not all, of their foliage clipped before transplanting to minimize respiration in the newly transplanted plant, being careful not to damage the apical growing point in the process.
Seed Maturation: Plants can get as tall as 3 to 5 ft (0.9 to 1.5 m) while flowering and may require staking in windy locations. Maturing seed on parsley umbels may look deceptively green for some time as the plant approaches full maturity. Also, parsley seed shatters easily at maturity and must be harvested promptly when ripe or losses will occur. Therefore, for many growers it may be a good practice to check the degree of starchiness in the developing endosperm of the seed to become familiar with other outward cues that reveal the time to harvest the plants.
Seed Harvest
Cutting, windrowing, and threshing the crop is identical to the process used for carrot.
Genetic Maintenance
Parsley is a biennial, and its seed is traditionally produced from plants that have been overwintered in the field. Any plants that flower or show any signs of flower initiation (apical stem elongation) or premature bolting during the first year should be viewed as suspect and should be rogued out (eliminated from the population). Selection should also be done in the first season for leaf type (intensity of leaf curl), leaf color, plant stature, and overall vigor, as these traits are most easily spotted during the vegetative growth period. Plants that exhibit disease symptoms, excessive insect damage, and poor overall health can be eliminated at any point during the biennial cycle. If you’re growing a root parsley type it is best to lift the roots either in the fall of the first year or in early spring of the second year in order to select for root characteristics. Root parsley has a rather unrefined, primitive root that commonly has some number of adventitious roots that wouldn’t be acceptable in its more sophisticated relatives, carrot and parsnip. Selection in this crop should be against roots with an excessive number of these adventitious roots and for well-filled roots with little or no discoloration.
Isolation Distances
The standard isolation distance of 1 mi (1.6 km) should be used between parsley seed crops of the same leaf type when there are no physical landscape barriers. In cases where there are significant barriers on the landscape between two crops of the same leaf type, it is possible to diminish this distance to 0.5 mi (0.8 km). As it is always possible to have some crossing at these distances, two parsley varieties of the same leaf type will suffer less varietal damage if crossed in the production of commercial seed.
If you are producing parsley seed of a different leaf type from the nearest neighboring parsley crop, then you will need to double the isolation distance to 2 mi (3.2 km) to ensure a high level of genetic purity if there are no barriers on the landscape. This increased distance is also necessary if you are producing a leaf parsley seed crop in the same district as a root parsley seed crop. When growing these divergent types the isolation distance can be decreased to 1 mi (1.6 km) when there are significant barriers on the landscape between crops.
Parsnip
The parsnip (Pastinaca sativa L.) is a native of Eurasia, from the region between the western Mediterranean and the Caucasus Mountains, where it has been grown for at least 2,000 years. It was used in both the early Greek and Roman civilizations but did not spread as far and wide via trade as many of the other Mediterranean crops that were grown by these societies. Its popularity is strong in some parts of Northern Europe and the UK, and it has been an important vegetable in parts of New England and eastern Canada since they were settled in the 17th and 18th centuries. It is especially popular in the cooler temperate zones, where it grows to its full potential in climates where lengthy, cool autumn weather produces sweeter, heavier roots.
Parsnip is a robustly growing biennial with a strongly aromatic taproot that is often larger than most types of carrots. Parsnips are grown, harvested, and stored much like carrots, though unlike carrots they can be left in the ground through the winter in most climates where they are grown. They are often harvested fresh from the ground for market until the ground freezes. Parsnips have an ability to convert stored starches into sugars with cold temperatures, and as the roots are relatively low in moisture they are able to freeze solid and be harvested for food or allowed to regrow as a seed crop when they thaw in spring.
‘Turga’ is a stout-rooted variety of parsnip that originated in Hungary.
Parsnip plants can achieve a height of 5 to 6 ft (1.5 to 1.8 m) and produce prolific numbers of compound umbels on primary, secondary, and tertiary branches on this indeterminate flowering species. Their small, greenish yellow flowers are less showy than the flowers of many other Apiaceae crops, but they are very adept at attracting a wide number of pollinating insect species. Their seed is fairly flat and slight and is famously short-lived, as its germination rate will usually start to drop within 2 years of harvest.
Parsnip seed is grown in climates similar to those preferred for carrots, though high-quality parsnip seed can be grown in climates that are somewhat cooler and shorter. Parsnip seed is grown in the cooler coastal areas of the Pacific Northwest of the United States and Canada, the Rhône Valley of France, New Zealand, and numerous small pockets across the parsnip-growing areas of Northern Europe, New England, and Canada, where growers maintain regionally important strains.
Crop Characteristics
Reproductive Biology
Parsnips are biennials that bear a single primary umbel at the terminus of the main floral stem, which is followed by highly branched stems with many successive secondary and tertiary umbels that continue to develop throughout the second season of reproductive growth. Perfect flowers are greenish yellow and are borne on broad compound umbels and have five petals, five sepals, five stamens, and two styles with nectaries at their base. Like carrots and other Apiaceae crops, parsnips are protandrous, meaning that fertile pollen will shed before the female stigma of the same flower is sexually receptive, thus decreasing the odds of self-pollination. Parsnips are largely cross-pollinated due to insect activity, but they will self-pollinate.
In most temperate climates the seed borne on the flowers of the primary and secondary flowers is the parsnip seed that most reliably matures. Depending on the length of season subsequent third- and even fourth-order umbels will form, but the opportunity for the seed on these later-setting flowers to fully mature is greatly reduced in many temperate regions.
Climatic and
Geographic Suitability
Parsnip roots are best produced in moderate climates where they can both germinate and produce much of their initial growth under moderate temperatures below 77°F (25°C). Soils must be kept moist for up to 3 weeks after sowing as parsnip seed can take from 2 to 3 weeks to germinate even at optimum germination temperatures of 65 to 68°F (18 to 20°C). As with other root crops, parsnips require an even supply of water throughout the season to produce good-quality roots where it is easy to distinguish the phenotypic characteristics of the variety. The climatic characteristic that sets parsnips apart from carrots and all of the other major biennial root crops is the fact that parsnip roots grown for seed can be left in the ground throughout the winter to freeze solid in most climates where they are grown.
The best climates for parsnip seed production across the two seasons of this biennial are similar to carrot, though successful seed crops can be matured during the second season in climates that are cooler than those required to get the best yields in carrots. In fact, climatic conditions during the second season are more akin to the conditions best suited to many of the brassica crops, where there are long mild springs and the summer temperatures don’t routinely top 80°F (27°C) (see chapter 8, Brassicaceae, “Climatic Adaptation”). As with all dry-seeded vegetable crops, parsnips thrive in the dry Mediterranean climate with low precipitation amounts from late June until mid-September. This climate significantly lowers the chances of any diseases forming on the seedheads as they mature. However, this means that reliable water must be applied with either a drip or furrow irrigation system; overhead irrigation may promote disease in the seedheads.
Parsnip seedheads, showing the differential maturation of primary and secondary umbels versus the smaller, later-forming tertiary umbels.
Seed Production Practices
Soil and Fertility Requirements
Parsnips are best produced in deep, rich, lighter loam soils with good water-holding capacity. Heavier or stony soils will have a tendency to produce crooked, branching, or malformed roots. Parsnips are similar to table beets or chard in their fertility requirements, responding to relatively high levels of fertility and a pH of 6.5 to 7.0 to produce the healthiest roots.
Growing the Seed Crop
The steps to produce parsnip seed are very similar to the steps used in carrot seed production (see Carrot, “Growing the Seed Crop”). Both the seed-to-seed and the root-to-seed methods are executed in the same way as is used for the carrot seed crop. The major difference is that it is much easier to use the seed-to-seed method for parsnips, as they are highly tolerant of freeze damage. This allows growers in much colder climates to use the seed-to-seed method with parsnips, and it means you don’t need to be as concerned with having smaller roots of a certain size to successfully go through the winter. This frees you from being as concerned about the timing for planting the crop in the first year. That said, remember that the roots from all root crops are best overwintered when they have not grown too large, as most older, larger roots have often accumulated more environmental damage (cracks, insect bites, and so on) and often have a lower chance of making it all the way through to producing a seed crop.
The other major difference in planting parsnips is the spacing that is used for seed production. Parsnip plants are somewhat bigger than carrot plants, both in the vegetable stage and during the reproductive stage, and therefore need to be spaced somewhat farther apart than do carrots for both parts of their life cycle.
Seed-to-Seed Method: As with carrot, seed should be sown sparingly in order to make thinning easier. Thinning can be achieved by blocking with a hoe or by cross-cultivating with a spring-tooth harrow across the field at a perpendicular angle to the rows when the parsnips are young but well-established seedlings. The goal is to achieve an in-row spacing of anywhere from 6 to 18 in (15 to 46 cm) between plants, depending in part on how early you plant them (hence, how large they’ll become in the first season) and in part on how tightly spaced you want them to be during the second reproductive phase of their life cycle. Traditionally, parsnips have been spaced 18 to 36 in (46 to 91 cm) apart in the row for the reproductive phase of their life cycle, but in recent years many growers have been spacing the roots somewhat closer, 12 to 18 in (30 to 46 cm) apart for flowering. So the grower can either plant and thin to this wide spacing during the first season or thin the crop to a closer 6 in (15 cm) spacing, allowing for a second thinning to every other or every third plant at the beginning of the second season. This allows the seed-to-seed grower to at least perform selection for the most vigorous, healthy parsnip plants coming out of winter. The spacing between rows can be anywhere from 24 to 48 in (61 to 122 cm) with the seed-to-seed method.
Root-to-Seed Method: The root-to-seed method is also performed for parsnips much as it is for carrots. With all root crops, the root-to-seed method has two basic versions:
1. The first version is to pull the roots in the fall and store them in a coldroom over winter for replanting them for seed production in the spring.
2. The second version is to overwinter the roots in situ, pulling them in the spring to replant into a seed production field.
Both of these versions of the root-to-seed method allow you to evaluate and select the best roots to replant for the seed crop. The great advantage of the cold hardiness of parsnip roots is that it is possible to use the second version of this method in a much wider range of climates than is possible with almost all other biennial root crops. Therefore, there are few growers who use the first version of the root-to-seed method, essentially choosing either the second version of this method or using the seed-to-seed method, both of which overwinter the roots in the soil as a form of storage. Because parsnip roots seem to overwinter successfully even in soils that freeze solid during the depths of winter, it is unclear what weather conditions will actually damage the apical growing point for the shoot, which is located in the crown of the root. In other root crops that can withstand a certain amount of freezing, it is sometimes the repeated freezing followed by thawing events that can damage this apical growing point; however, it has been hard to find any written reference or handed-down wisdom as to what specific set of challenges will significantly damage a parsnip root to the point where it won’t regrow in the spring.
Upon replanting the roots in the spring for the root-to-seed method, the roots are often planted at anywhere between 18 and 30 in (46 to 76 cm) apart within the row, depending on the eventual full size of the variety and the between-row spacing. The between-row spacing in the root-to-seed that was once used between plants was as wide as 6 ft or 72 in (1.8m/183 cm). Today most growers use a spacing of 36 to 48 in (91 to 122 cm) between the parsnip rows.
Seed Harvest and
Seed Cleaning
Most aspects of seed harvest and seed cleaning are virtually identical to carrot (see Apiaceae, “Seed Harvest” and “Seed Cleaning”). The only significant difference is that parsnip seed will shatter from the umbels more readily than carrot seed when both are equally mature. Therefore, care must be taken to cut and harvest the seed in a very timely fashion. Growers will often windrow the plants onto landscape fabric that is porous to precipitation when curing the seed before threshing.
Caution: A word of caution when harvesting and handling parsnip plants, especially at the time of seed harvest. Parsnip stems and leaves contain a compound, furanocoumarin, within the sap that causes extreme rashes in many people. This rash is akin to what’s experienced when people come into contact with poison ivy or poison oak. This chemical is photosensitive and may be intensified when the affected skin is also exposed to sunlight. There is evidence that furanocoumarin in the sap is more concentrated in the relevant tissue during the reproductive phase of the parsnip’s life cycle. The resultant rash can often last for weeks, if not months. All workers handling parsnip plants at the time of seed harvest should wear long-sleeved shirts, long pants, and gloves and wash these items after use.
Genetic Maintenance
The characteristics that are important when maintaining parsnip varieties are much the same as many of the traits important for carrots (see Carrot, “Maintenance and Selection of Genetic Stocks”). Traits such as root shape, root smoothness, and root length, as well as foliar characteristics like top height, top size, erect growth habit, foliar color, and low incidence of disease, are important. The major root disease of parsnips, canker, if present in your area, can give you an opportunity to select roots that exhibit a lower incidence of this widespread malady. Another important trait to be sure to check for is root shape. Parsnips have a unique tapered shape that needs to maintained. Also important to monitor is the smoothness of the surface of the roots, as they can be rough due to large lateral root scars. Selection for smooth roots should occur every time roots are pulled and evaluated using the root-to-seed method to maintain a reasonable level of smoothness in any variety that you are producing.
Isolation Distances
Parsnips are insect-pollinated, and like most crops in the Apiaceae they are very attractive to a wide diversity of pollinators. This is relevant, as all members of this family grown for seed in most temperate climate settings will attract insects from a broad perimeter around the field in which they are planted. This is especially true of organically grown seed crops on farms with crop species diversity. However, this also means that you will need to be careful in determining isolation distances if you plan to grow more than one parsnip variety for seed or if there is any wild parsnip in the area.
The standard minimum isolation distance of 1 mi (1.6 km) for insect-pollinated crops should be used between parsnip crops of the same crop type, when there are no physical barriers on the landscape. In cases where there are significant barriers on the landscape it is possible to diminish this isolation distance to 0.5 mi (0.8 km). The distinction of different crop types among parsnip varieties is minimal, as most commercial parsnip varieties at present are much alike in their phenotype. There are, however, some differences in the degree of taper and the length of the parsnip root between different varieties that may warrant increased isolation distance when two seed crops with different shapes are produced in the same area. The other major difference that can exist among parsnip varieties is in their disease-resistance profile. There has been some breeding work in recent years to incorporate canker resistance into a number of parsnip varieties. If seed of two parsnip varieties with differences in their levels of canker resistance or in their shape were going to be produced in the same district, then it would be wise to double the minimum isolation distance used between crops to 2 mi (3.2 km) without barriers and at least 1 mi (1.6 km) if there are significant barriers on the landscape to interrupt the movement of pollen.