The Amaranthaceae or goosefoot family contains several economically important species of crop plants and a number of the most prominent and pernicious weeds worldwide. The important vegetable crops in this family are beets, spinach, and Swiss chard. Minor vegetables include orach and Good King Henry. These crops are all from the Old World and have probably been used in agriculture in some form since ancient times. Several New World domesticates from this family have played an important role in the agriculture of the Americas, with quinoa historically being the most important grain crop in the Andean highlands, where it thrives at altitudes above 8,000 ft (2,440 m).
All of the vegetable members of the goosefoot family have leaves that have traditionally been harvested for their use as cooked greens or potherbs. The garden beet is also harvested for its fleshy, sweet roots and is an important root vegetable in temperate climates across the globe. With the increase in demand for cut leaves for bagged salads from local farmers and large produce growers alike, the demand for seed of all of these crops for their succulent and often colorful greens is rapidly increasing.
The plants of the Amaranthaceae are dicotyledons. The crop plants are similar in many of their characteristics, usually having alternate and simple leaves that form a large rosette in the vegetative phase of their life cycle. All of the cultivated chenopods are wind-pollinated, producing copious amounts of pollen that is capable of traveling several miles and remaining viable if environmental conditions are just right. An oft-repeated fact, that beet pollen was collected by an airplane at an altitude of greater than 3 mi (5 km) above sugar beet fields by beet researchers demonstrates the potential range of the pollen.
The Amaranthaceae are all dry-seeded crops, and their seed is most successfully grown with little or no precipitation during the flowering and seed maturation stages of their life cycle (see chapter 15, “Cool-Season Dry-Seeded Crops”). Most of the commercial seed production of these crops is done in cool temperate regions with dry weather in summer and early fall. Major seed production areas for beets, chard, and spinach include coastal regions of the Pacific Northwest in the United States, central Denmark, Southern Europe, and the South Island of New Zealand. However, smaller-scale production of regionally important varieties is common in a number of regions around the world where these crops are culturally significant. Beet seed production for many varieties popular in Eastern Europe and the Mediterranean Basin is undoubtedly extensive, even in areas with less-than-ideal conditions for growing Beta spp. seed.
Family Characteristics
Reproductive Biology
The cultivated Amaranthaceae include both annuals and biennials and consist of dry-seeded crops that most successfully mature their seed over an extended dry period in the late summer and early fall. The inflorescence of these crops has flowers that are small, inconspicuous, and borne in the axils of branches and leaves. Beets and Swiss chard have perfect flowers that almost always outcross due to a genetic trait for self-infertility. Spinach is naturally dioecious, with most open-pollinated populations having a balanced sex ratio of the two unisexual types. The dioecious habit in spinach is indeed a foolproof biological way to ensure cross-pollination.
The flowering habit of the Amaranthaceae is indeterminate, and once initiated, flowering will continue until harvest or frost. Hence seed will be maturing continuously throughout the rest of the season, with a certain percentage of it that is immature at harvest. Therefore you must monitor the relative maturity of your beet, chard, and spinach seed, understanding that at least 20% of the seed that has set won’t be fully formed when you harvest the crop.
Life Cycle and
Climatic Adaptation
The garden beet and Swiss chard are typical biennial plants producing a relatively large rosette of leaves and fleshy storage root during the first season of growth and one or more branched seed stalks during the second season. Both beets and chard thrive in cooler climates, with their most vigorous growth occurring in spring and fall. The goal in seed production is to produce a moderate-sized storage root in the late summer and fall of the first year that can be either overwintered in the ground or stored in a root cellar or coldroom for replanting in the spring. Swiss chard, though not grown as a root vegetable, does produce a substantial storage root. When grown for at least 90 days chard plants will produce roots that can be stored like beets for up to 5 or 6 months in a root cellar or cooler. Like all biennials, beets and chard require a period of vernalization (cold treatment) of at least 8 weeks for flower initiation during the second year of their life cycle. And they must have a substantial root with an intact apical growing point for both the shoot and the root. The three methods for overwintering beets and chard are the same as outlined for Apiaceae crops (see chapter 6), as indeed beets and carrots are treated much alike in most regards concerning seed production (see the Garden Beet section for specific differences).
Spinach is an annual that is almost always planted in spring as a seed crop. It must be planted early enough in the spring to produce a large enough plant to support a hearty seed yield (or produce a hearty amount of pollen if it’s a male plant). Spinach flowering is initiated primarily by daylength. Days with at least 14.5 hours of light will initiate the development of the male and female flowers and inflorescences in many standard spinach varieties developed before the 1990s. Most newer spinach varieties are considerably more bolt-hardy. This means that most older spinach types will often be noticeably bolting by late May to early June at latitudes above 40 degrees, with the biochemical initiation occurring quite a bit earlier, especially at higher latitudes.
Seed Harvest
The chenopods share the trait of indeterminate flowering that translates to sequential ripening of the seed at the end of the season. A percentage of the seed that sets later in the season, easily 20% or more, will never mature. Therefore the timing of the seed harvest is a compromise of patience to get the highest amount of mature seed while not waiting too long and risking the loss of quality to inclement weather or loss of the most mature seed from shattering. As with most crops with indeterminate flowering grown in temperate climates, the earliest fraction of seed to mature is almost always superior—larger, with a higher germination percentage and greater seedling vigor.
Determining the time of harvest for beets, chard, and spinach is usually done via a visual assessment. In general the color of the seed is used as an important indicator of maturity. The seed of these three crops will turn tan to tannish brown in color if matured under dry, favorable conditions, and turn a darker brown when matured with unwanted late-season precipitation. Many growers will wait till between 60 and 80% of the seed on a solid majority of the plants in the field has turned brown to begin harvest. While this method can successfully result in a high-quality seed crop, there are several ways to check the endosperm of chenopod seed to get a more accurate picture of the relative maturity of the seed (see specific instructions under “Seed Harvest” for each crop).
At harvest mature chenopod seed crops are cut and laid in windrows on cleared, cultivated ground or on tarps or landscape fabric. Curing the seed in windrows can take anywhere from 5 to 10 days depending on weather. If wet weather threatens it may be necessary to move the crop to a drying shed, greenhouse, or seed dryer. Threshing is often done by manually feeding cured plants into self-propelled combines or stationary threshers. Cutting and swathing these crops is best done early in the day to take advantage of dew to reduce losses from shattering. This also reduces the amount of small pieces of stem the size of the seed that ends up in the seed fraction after the scalping step is completed.
Seed Cleaning
Chenopod seed is usually scalped as a preliminary step in the cleaning process. Scalping is the first step in the seed cleaning process where the bulk of the leaves, stems, and any debris is eliminated when the first cut of the freshly harvested material is run across a large screen with very large holes or slots. This should be done soon after threshing to eliminate any moisture that is held in the leaf and stem tissue prevalent in freshly threshed beet, chard, and spinach seed. Seed of these three crops frequently needs some degree of drying soon after harvest with the onset of cooler wet weather at the end of the season in the cool climates that are suitable for seed production. Chenopod seed is usually then rubbed in large, cannon-like cylinders that have a rotating shaft with large studs, which actually rub the seed against one another while under pressure in the shaft. These crops have seed that is frequently borne in clusters that can fuse together and are often also fused to pieces of the stem; rubbing is very important to break these clusters. In addition beet and chard seed has a corky outer surface from the dried flower bracts that fuse and form their characteristic multigerm seed balls. These are frequently rubbed until the multigerm seed balls are smoothed and rounded, a process called decortication. Decortication can also have the odd side benefit of damaging one or two of the multigerm embryos of the larger seed. This is viewed as a benefit in the seed business, as it may reduce the number of sprouts in the larger seed balls from three or four sprouts to one or two, thus making it less likely for a vegetable grower to get too dense a stand at planting.
Isolation Distances
The crops of the Amaranthaceae have pollen that is known for its ability to travel great distances. These crops are predominantly wind-pollinated, and their pollen is relatively small, light, and easily carried by the wind. These crops also produce copious amounts of pollen. For these reasons, wind-pollinated crop species need a greater isolation distance between seed crops of the same species than insect-pollinated species. Certainly the chenopods require at least 2 mi (3.2 km) of isolation between crops of the same type when grown in the open and 3 or 4 mi (4.8 to 6.4 km) when growing different types of the same crop species or when isolating stockseed production from other seed production crops of the same species (see chapter 13, Isolation Distances for Maintaining Varietal Integrity). However, it should always be remembered that these isolation distances are not absolute, and there may still be a small amount of crossing even at these higher isolation distances, especially with these wind-pollinated crops.
The humble vegetable known simply as the beet in North America is also known as the garden beet, red beet, table beet, or beetroot to distinguish it from both sugar beets and fodder beets. The sugar beet is grown for its high sugar content and the fodder beet, also called mangold, mangel, or mangel-wurzel, for its nutritional tops and roots, which are used as animal fodder. These three root crops, along with the leafy vegetable Swiss chard, are all members of the same species, Beta vulgaris. Despite being distinguished by various subspecies designations by taxonomists, these four crops are all fully sexually compatible and will readily cross when flowering in proximity to one another.
The garden beet is thought to have originated in the western reaches of the Mediterranean region in southwestern Asia and was introduced into Europe during the Middle Ages.
The earliest cultivated beets were probably used as a leafy green vegetable. There is some indication that the roots of this ancestral form of the crop were used for medicinal purposes. It has been speculated that the original form of the crop was an annual, probably a winter annual, and only through selection for a food plant that could be stored through the winter as the crop spread northward did the beet develop an enlarged storage root and become a biennial.
The ‘Yellow Intermediate Mangel’ is a modern example of the mangel-wurzel, an old large-rooted form of field beet used primarily as animal fodder.
The first descriptions of garden beets with fleshy, edible roots are from Germany in the 16th century. It wasn’t until the 18th century that written accounts of garden beet cultivation across Europe became common. By the 19th century beets were an important crop throughout Europe, North Africa, the Middle East, parts of western Asia, and North America. In 1885 Vilmorin-Andrieux devoted 15 pages to garden and fodder beets in his classic text The Vegetable Garden, which describes the common vegetable varieties used throughout Northern Europe at the time. By then both red- and yellow-colored beets were being described, and root shapes for garden beets were described as either “turnip-rooted” or long. The turnip-rooted types were globe-shaped or flattened globes; the long types were usually more pointy or cone-shaped than the modern cylindrical types. Vilmorin-Andrieux also lists several named “intermediate” types, “being intermediate between the garden and field types,” which are described as being large and often forked like mangels, but “of good quality for table use.”
‘Pronto’ is a high-quality fresh-market beet with robust green tops. Its green tops need regular genetic selection in order to maintain this elusive trait. Photo courtesy of Micaela Colley
With the onset of a thriving commercial seed industry in North America and Europe in the early 20th century, red, globe-shaped beets became the dominant form in these markets. Most garden beet varieties developed in the last 100 years have been either fresh market types with taller, robust tops or processing varieties with shorter tops and an emphasis on dark root pigmentation. Traditionally beet roots have been used as a cooked vegetable or pickled. Mature beet tops or “greens” have been cooked or occasionally used in salads. With the advent of prepared or bagged salads the use of beet greens grown for the baby leaf market has increased dramatically. This has greatly increased the amount of beet seed grown commercially, with a large increase in the organic beet seed produced.
Crop Characteristics
Reproductive Biology
The garden beet is a biennial, normally requiring two growing seasons to produce seed. During the first year of growth it produces a rosette of leaves and a fleshy taproot. During the second year it develops a seed stem that is 3 to 5 ft (0.9 to 1.5 m) tall with extensive branching and can cover a diameter of more than 3 ft (0.9 m) on the ground.
Flowering is initiated by a cold treatment of the roots, or vernalization, after the first season’s growth (see chapter 3, Understanding Biennial Seed Crops, “Vernalization”). The vernalization requirement for beets is approximately 8 full weeks of temperatures at or below 50°F (10°C). This, coupled with lengthening daylight in spring, will promote flower initiation and subsequent flowering. The garden beet is predominantly wind-pollinated and has extremely light pollen that is easily carried long distances by the wind. Perfect flowers are borne in most of the leaf axils of the large branching plant. They usually occur in clusters of two to five, with one bearing an extended bract that encircles the cluster. As this single bract dries it forms a corky, irregularly shaped multiseeded fruit. This is what is commonly called the seed ball or multigerm seed in the seed trade. As this seed ball is capable of producing two, three, four, and even five seedlings, it is hard to achieve a well-spaced stand even with precision planting. Monogerm varieties have single flowers borne in bract axils, therefore no fusing of multigerm seed balls. Many vegetable growers have avoided monogerm cultivars, complaining of poor seedling vigor. If true, this is a serious hurdle for monogerm seed to cross in gaining acceptance by organic farmers.
The perfect flowers are protandrous, with the anthers of a particular flower maturing and shedding pollen for 2 to 3 days before the gynoecium of that flower matures and the stigma becomes fully receptive for up to 2 weeks. The small, greenish flowers are quite compact as the anthers have very short styles. They are not showy, as is normal for wind-pollinated species. Nectar is produced and insect pollination is common, although the wind accounts for most pollination events. Beets are self-incompatible, and therefore any individual beet plant will not receive its own pollen to fertilize its ovules and produce seed. Each individual plant must have pollen from a genetically different individual in the population (or another population) to produce viable seed. This encourages almost complete cross-pollination between individuals in a population, although rare individuals capable of self-pollination have been found and used in hybrid breeding programs.
Climatic and
Geographic Suitability
The garden beet is a cool-season crop that thrives when grown at moderate temperatures between 60 and 72°F (16 to 22°C), which encourages steady, vigorous growth. When grown as a spring-planted vegetable, beets can tolerate hotter temperatures as they mature a root crop. The beet seed crop, however, is much more sensitive to heat during the second seed-bearing season of the biennial cycle. In order to produce high-quality yields of vigorous seed with high germination rates beet seed crops should be grown in regions where summer temperatures don’t usually exceed 75°F (24°C). The best beet seed production locales have cool, wet spring weather to establish a sturdy frame of vegetative growth, followed by cool, relatively dry summer weather to support optimum pollination, fertilization, and seed development. An extended dry period in late summer and into early fall is ideal for beet seed crops to minimize seedborne diseases and allow the crop to fully mature. Beet seed that avoids most precipitation as it matures also retains a healthy mahogany brown color at harvest. Important production areas include the Skagit Valley and the Salish Sea basin of maritime Washington and British Columbia. Beet seed is also grown commercially in the Rhône River Valley of France and on the South Island of New Zealand. As the garden beet is a very important crop across Eastern Europe and in many temperate regions of eastern Asia, there are undoubtedly a number of places where seed of regionally significant varieties is being produced for commerce and subsistence use.
A garden beet with irregularly shaped fruit or “seed balls,” developing in the plant’s leaf axils.
Seed Production Practices
Soil and Fertility Requirements
Beets grown as a vegetable crop are best suited to a fairly deep, well-drained sandy loam. Growing the first-year roots on a friable soil of this quality will enable the seed grower to select for the shape of the roots before using them as stecklings the following season if using the root-to-seed method (see chapter 6, Carrot, “Root-to-Seed Method”).
Roots can be replanted in heavier soils in the second year for seed production. In fact, many growers claim that a heavier clay soil will produce a higher seed yield. The soil pH for beets is a narrow range, between 5.8 and 6.2, for optimum health. Beets are salt-tolerant; cropping is possible on soils that are too saline for many other crops. They are also very sensitive to boron deficiency in the soil, which can cause crown rot, blackening of leaf margins, or heart rot within the roots. Boron deficiency is most prevalent in alkaline soils. In seed crops, the amount of available nitrogen should not be too high in order to avoid excessive vegetative growth before bolting, as this promotes lodging of the plants during seed set. Well-maintained agricultural soils high in humus and microbial populations will supply adequate nutrients and water over the long seed production season.
Beet seed is produced using the two basic methods, seed-to-seed and root-to-seed, that are used for carrots, parsnips, and other biennial root vegetables (see chapter 6, Carrot, “Seed-to-Seed Method” and “Root-to-Seed Method”). The seed-to-seed method for beets has not been as successful as it has been for carrots and some of the other biennial seed crops, however, especially in the traditional beet seed growing regions. The seed-to seed method was used exclusively in the Skagit Valley of Washington (the largest garden beet seed production area in the United States) until the 1940s. The production practice of having the first-year beets overwinter in the field to produce seed in the same field, where they could easily infect any new beet crops being planted nearby with any parasitic organism (insect or plant pathogen) that they might harbor, proved to be a disaster. The Skagit Valley beet seed growers at that time were experiencing an increasing problem from beet mosaic virus (BtMV), a viral disease that causes mosaic patterns and zonate rings of leaves, and that will eventually cause foliar necrosis, which in turn leads to stunting and poor seed quality and yield. It was determined that this disease was spreading from the second-year seed-bearing beet fields to the new, first-year root crop in nearby fields via both the green peach aphid (Myzus persicae) and the black bean aphid (Aphis fabae). The BtMV and the aphid vectors were being harbored from one season to the next on the live plants overwintering in the fields. These plants were acting as a “green bridge” for both BtMV and the aphids, allowing them to pick up right where they left off in the previous season as soon as the growing season started. The solution was for all of the beet growers to agree to discontinue the use of the seed-to-seed method and to produce their roots outside of the valley. This would mean no beet plants to serve as a “green bridge” through the winter and no first-season beets anywhere in the valley to pick up any parasites in the first season to be spread in the second season.
Seed-to-Seed Method: The basic protocol for the seed-to-seed method for all biennial root crops is described in chapter 6, Carrot, “Seed-to-Seed Method”. The seed-to-seed method for beets can be problematic in areas where large-scale beet seed production is taking place, due to the “green bridge” effect described in the previous section. However, there are instances where farmers who are isolated from other beet (or other Beta vulgaris crops) production areas can use the seed-to-seed for production across a number of years, so long as they monitor their crops for disease symptoms and utilize occasional seasonal breaks where they don’t have any beets in the field. Another important aspect of potentially monitoring seed-to-seed cropping in beets is to remember that the aphids and other vectors move the viruses like BtMV, beet yellows (BYV), beet mild yellows (BMY), and beet curly top from field to field depending on weather patterns and air currents. Therefore, using as much isolation as possible in your own root and seed fields, even if you are isolated from other growers, is very important in controlling these pathogens.
As with carrots, the seed-to-seed method requires less labor and is simpler than the root-to-seed method. The drawbacks to using this method for garden beets are essentially the same drawbacks as exist for all of the biennial seed crops. The first is the fact that the roots must overwinter in the field. As table beets are generally less cold-hardy than some of the other biennial crops such as carrot, rutabaga, or cabbage, you must be knowledgeable about the ability of the crop (and the specific variety) to survive throughout the winter in your region. Most table beet varieties will survive temperatures down to a range of 24 to 27°F (–4 to –3°C) without permanent damage, depending on the duration of the cold and the severity of the freeze–thaw cycles.
The second drawback to the seed-to-seed method is the inability of the grower or the seed company to perform selection on the crop’s roots to maintain varietal integrity. As is the case with all biennial root crops that are grown for seed, selection of the roots is very important in maintaining a true-to-type variety unless you’re starting with well-maintained stockseed (see chapter 17, Stockseed Basics).
Root-to-Seed Method: The basic protocol for the root-to-seed method for all biennial root crops is described in chapter 6, Carrot, “Growing the Seed Crop”. As with all biennial root crops, this method allows you to evaluate the roots and select the best ones for planting stock. The roots must be acceptable phenotypically and must be free of any disease, pests, or physical damage in order to store properly under any of the storage methods outlined for beets. Phenotypic selection characters are discussed in the “Genetic Maintenance” section.
Trimming beet roots for storage: (left) untrimmed beet root, (right) beet root trimmed properly for storage (compare to carrot stecklings). Photo courtesy of Jared Zystro
Beet roots are better suited to the root-to-seed method than many other biennial crops because the roots store so well and for relatively long periods of time if stored properly (see chapter 3, “Preparing Roots for Storage”). Beet roots are also ideally suited to having a piece of the side of the root cut off to select for internal characteristics like the intensity of color and the presence of zoning (see “Genetic Maintenance-Root Color”).
Seed Harvest
Seed Maturation: Beet seed formation usually starts anywhere from 6 to 10 weeks after flower stalk initiation. As the flowering habit is indeterminate, flowering and subsequent seed maturation will continue until harvest or frost. Because beet seed matures sequentially, the percentage reaching full maturity at the time of harvest will usually not exceed 75% of the total seed crop. The earliest seed to set will often mature several weeks before the bulk of the seed on any given plant has matured. This first seed set is usually of a high quality and has a high germination rate, but it may readily shatter as the bulk of the crop is maturing. You must determine when the maximum overall maturation has occurred, without losing a significant amount of the earliest-maturing seed. Cool, wet weather can often occur during the late season, and the seed maturation period for beets in the Pacific Northwest makes it even more important for growers there to closely monitor the seed maturity and not harvest too early or too late. Early harvest may result in a percentage of seed that is not fully mature. Harvesting seed past the optimum time period may result in reduced yield and seed quality due to seed shattering and an increased incidence of seedborne diseases.
A standard method used to judge maturity of the beet seed crop is a visual assessment of the color of the seed ball (a multiple-seeded fruit resulting from the fused dry corky bracts of two or more flowers that occur at the same node). Harvest should occur when between 60 and 80% of the seed balls on at least 90% of the plants in the field have turned a tannish brown shade, typical of mature beet seed. Unfortunately this method may sometimes be inaccurate due to the potential effects of the environment or the genetic variation of the particular beet variety being produced. In a number of environments the beet seed balls will turn a darker shade of brown, sometimes before they reach full maturity. This often occurs with higher-than-usual levels of precipitation during the final weeks of seed maturation. This darkening may be due to saprophytic bacterial or fungal growth on the corky bract tissue of the seed balls. Depending on the pathogen this darkening may not be harmful to the seed, but it seriously impedes visual assessment of beet seed maturity. There is also considerable variation among varieties for the degree of browning of the seed that occurs during the maturation process. Some beet varieties may retain greener hues than others, even when fully mature.
The beet seed of commerce is usually a multigerm dried fruit that is an aggregate “seed ball” composed of two to five seeds.
In order to make a more accurate assessment of the maturity of the seed it is best to check the relative maturity of the endosperm of the seed. The endosperm, which grows concurrently with the embryo, must be fully developed to produce viable, fully mature seed that will grow vigorously and maintain a high germination percentage through its expected storage life. The starchy endosperm can be monitored through the maturation process by cracking open any one of the several seeds that occur within each beet seed ball. The best way to determine the maturity is to squeeze a small amount of the endosperm out of the cracked seed and visually inspect it. If the endosperm is viscous and appears translucent or milky, it is not close to maturity and will require at least 3 to 4 weeks to mature. Sometime after this the endosperm will start to appear grayish and waxy, what is often called flinty, but it is still not close to maturity. Only when the endosperm becomes starchy, with a true solid white color and a firm texture, is the seed very close to maturity. A majority of the seed—at least 70 to 75% of the seed on a given plant—must be at this advanced starchy stage before you consider harvesting.
Seed Harvest: Beet plants in full flower can have a stature of 3 to 6 ft (0.9 to 1.8 m) in height and can often cover a diameter of more than 3 ft (0.9 m) on the ground. The commercial beet seed crop is rarely staked, so there is a tendency for the crop to lean in all directions, thereby making mechanical cutting or swathing nearly impossible without causing excessive amounts of seed shattering. Because of this, many growers elect to perform the initial harvesting of the crop by hand. Crews walk through the field pulling plants by hand and laying them into several windrows across the field. In some cases the harvesters use machetes to cut the remaining beet root and root mass from the plant, to minimize the chance of getting soil in the seed during the subsequent threshing. Other growers choose to leave the root mass attached, as the root may still supply some energy in the final ripening that takes place in the windrow. This initial harvesting process is ideally timed to coincide with a subsequent period of fair weather for the after-ripening of the seed in the windrow.
The seed plants should be placed in the windrows in such a way that they receive sufficient airflow to allow even drying, even with heavy dew or light rains that may occur during this after-ripening. This is important, as beet windrows are not commonly turned; seed can easily shatter during turning. Depending on the importance or value of a particular beet crop, it may be worthwhile to place the crop onto landscape fabric or some other comparable porous material in order to catch any seed that may shatter during this period. The use of porous material is important to ensure that any precipitation or moisture accumulation will quickly be drawn away from the seed.
A mature beet seed crop that is swathed and drying in windrows in the Willamette Valley of Oregon.
The plants should remain in the windrows for 7 to 10 days. After this drying period threshing can be done using a belt thresher, a stationary rotating thresher, or a self-propelled combine that is manually fed. Threshing should be done early in the day, midmorning in most climates, as light dew on the plants will prevent much of the potential shattering that can occur when the plants are picked up for threshing. The moisture can also lessen the amount of stems that break and lessen the size of the broken pieces that occur during threshing, thereby saving much time in subsequent seed-cleaning steps to remove them. Threshed seed should then go through an initial screen cleaning or scalping to remove large leaf tissue, stems, and soil clods that can hold moisture. Further drying of the seed crop should occur at this point in a well-ventilated warm space with supplemental heat as necessary.
Manually feeding beet plants through a belt thresher in the field.
Beets are a cross-pollinated species with lots of inherent genetic variation. In order to maintain adequate genetic diversity and elasticity in any open-pollinated beet variety, it is important to harvest seed from a minimum of 120 to 200 plants each time that you reproduce a variety. This will help ensure that you do not severely shift the genetic frequency of any important traits that may not be obvious in your environment of selection and also ensure that the variety will maintain vigor and avoid inbreeding depression. The initial population size should reflect the intensity of selection activities. For instance, if a variety has been well maintained and requires very little selection to keep it true to type, then beginning with a population of 250 plants before selection will easily yield 200 selected plants. On the other hand, if a variety has a large percentage of off-type plants that need to be eliminated, it might require an initial population of 400 or more to derive a final population of 200 selected plants at a selection intensity of 50%.
Selection Criteria
The practice of trait selection of any crop is related to the needs of the farmer in a particular area, the environmental pressures of the production region, the cultural practices utilized, and market demands. While vegetable breeders normally concentrate on traits for farmers who grow the crop as a vegetable, it is also possible to select for traits important in the reproductive stage of the plant’s life cycle. Therefore, when someone is developing and maintaining varieties for organic systems, the selection criteria should include traits that are necessary for both the organic vegetable farmer and the organic seed producer. Selection should be done at several points in the life cycle whenever possible, including at the seedling stage, at the market or eating stage, and during flowering, to maximize reproductive health and seed yield.
To select for root qualities, when approximately 80% of the beet roots in the first-year root nursery are of marketable size, the roots should be pulled and placed neatly on the beds for evaluation; keep them out of direct sun until they are replanted. Root selection on a cloudy, cool day is ideal. Selecting roots is best done with good knowledge of what “the norm” is for the phenotype (appearance) of each variety. Selection to a standard varietal type is the major objective in commercial production of established varieties. If a variety is adequately uniform at the outset of your seed production endeavor, then you can expect to discard approximately 10 to 20% of the roots, simply to maintain varietal integrity. If the variety is not uniform due to lack of prior selection (or poor selection), then expect to select out as much as 50% of the roots as off-types. Selection for improvements of market characteristics is always best done at the market stage.
Seedling Vigor: Seedling vigor and early robust growth are important to organic farmers, as these traits affect the plant’s ability to compete against weeds, resist seedling diseases, and contribute to overall plant health. Vigor can be improved over several cycles of selection. Selecting for the quickest, earliest seedlings to emerge is the first step, but seedling selection should also include recognition of shape, size, color, and ability of the seedlings to grow under less-than-optimum conditions. This selection should occur soon after emergence and may be coupled with the initial weeding and thinning of the plot.
Leaf Size, Shape, and Color: While many seed growers do not pay attention to the leaf characteristics of beets, these traits are very important to vegetable growers who market bunching beets. Beets are generally classified as either short-top types, with tops that are often 6 to 8 in (15 to 20 cm) tall, or tall-top types, with tops 10 to 14 in (25 to 36 cm) tall. Selection of the tops for height within each of these categories is best done before the roots are pulled. Tops also vary in shape, from the narrower strap-leaved types to the wider heart-shaped-leaf types, and require regular selection, which is best done while the crop is standing. Leaf color can range from deep green to medium green to a largely red hue (for instance, ‘Bull’s Blood’). For bunching types the darker green color is desirable, as the lighter shades and reddish coloration are often associated with a product that isn’t as fresh as the darker green type. Also, cooler fall weather will often promote a blotchy reddening of the leaves that many people associate with leaf diseases or decline of the plant. This trait is more prevalent in some beet cultivars than others, and selection for darker green leaves that resist reddening into the fall has been successful when practiced.
Root Shape: Table beets come in an array of shapes, from long cylinders to rounded spheres, flattened globes, and roots that are shaped like a toy top. The size and width of the taproot at the bottom of the beet will also affect the shape of the beet; for instance, a top-shaped beet often has a pronounced, thick taproot. If the shape is not regularly selected, then the unique shape of a variety can be lost within a couple of generations. When selecting for shape don’t be overly concerned trying to get the perfect shape in each root; no two roots are the same and each shape is an approximation of the ideal shape for the variety.
Root Color: Table beets include red, pink, yellow, and white varieties. There can be differences in the shades of these colors and the intensity of the pigmentation. The color is somewhat apparent from viewing the exterior of the root, and you can make an initial selection in this way. However, if significant improvement in root color is desired, then you may select more precisely for the intensity of root color by cutting them open to see the interior. In order to do this and still be able to replant the beet, it is imperative that you do not cut into (or near) the apical growing points of the crown or the root. However, by cutting a slice of the root off the side of the beet (a “cheek”), you will be able to observe the interior color with no damage to the root. The piece of the root that is cut off can also be used for tasting and selection for flavor.
You can now leave the beet roots out in a cool, dry, shady spot for several hours to let the cut surface suberize or heal before it is planted. Suberin is a waxy substance that forms fairly quickly in damaged plant cells to prevent water from penetrating the tissue. The roots can then be replanted or stored for a short time before replanting. This evaluation for color of the cut roots should always be done at the end of the storage cycle soon before replanting the roots, as long-term storage of any damaged tissue is riskier than storing sound tissue.
Root color can be evaluated by cutting off a “cheek,” or side, of the beet. This can be done shortly before replanting the roots in any of the versions of the root-to-seed method. In this case, it is possible to judge the color intensity of the “rings” of a ‘Chioggia’ type (root on right). Photo courtesy of Jared Zystro
Root Crown and Smoothness: The size and rough appearance of the crown of a beet can contribute greatly to its overall appearance and marketability. A large crown that does not have good definition and has rough outer margins that extend across much of the top of the root is not desirable in a fresh market beet. This characteristic also reduces the amount of harvestable tissue in the beet root for fresh market sale or processing. The outer tissue of the entire root may also have an unappealing roughness for the fresh market. This may be due in part to one or more of the common diseases of beets but also appears to be a heritable trait of some beet varieties. Selecting for a smoother root surface has been effective in some beet varieties.
Beet pollen is capable of traveling several miles in the wind. The garden beet is predominantly wind-pollinated; its pollen is small and light and well adapted to being spread in this way. While insects are sometimes attracted to the sweet nectar and pollen that beets produce, they account for only a very small amount of the cross-pollination that can occur with the wind. Beets and the other chenopods have large numbers of flowers per plant and produce large amounts of pollen that can be seen blowing across seed production fields as a yellow dust during peak flowering. All of these factors make it necessary to increase the isolation distance over the recommendations for insect-pollinated crops. In the 1930s C. F. Poole of the USDA studied the distances that beet pollen can travel and concluded that under ideal conditions it can travel over 12 mi (20 km)! During the same decade other agricultural scientists collected sugar beet pollen at an altitude of 3 mi (5 km) above sugar beet seed fields.
In commercial beet seed production in the Salish Sea area of Washington the isolation between two different red beet varieties is 1 mi (1.6 km) if they are both open-pollinated (OP) varieties; while it’s 2 mi (3.2 km) if they are both hybrid varieties or if one is a hybrid and the other is an OP. This disparity assumes that hybrid seed is intrinsically more valuable and deserves to be kept at a higher level of purity than seed of OP varieties. This is an outmoded idea that is common in vegetable seed production areas, where the practices have been dictated by the business-driven notion that hybrids are always superior. Well-maintained OP varieties that have improved adaptation and market traits that fit the bill for the organic farmer are capable of going toe-to-toe with hybrid varieties in many instances. Therefore, I am not recommending shorter isolation distances for OP varieties than for hybrids.
Another important consideration in avoiding cross-pollination in a beet seed crop is to be aware that during the first year of the biennial cycle, all Beta vulgaris crops may flower prematurely if exposed to excessive cold temperatures. This produces pollen from plots that are not normally considered in calculating isolation distances. Many vegetable growers know that a percentage of Swiss chard plants grown as a vegetable will bolt in the first season if planted early in the spring (‘Rhubarb’ chard is notorious for this). While this doesn’t happen as often with sugar beets or garden beets, these crops will have an occasional beet plant that is bolting prematurely for the same reasons.
Isolation Distances for Red Beets: The minimum isolation distance between any two standard beet varieties with the same root color should be 2 mi (3.2 km) if grown in open terrain with few or no physical barriers. If physical barriers do exist, then it is possible to drop this isolation to 1 mi (1.6 km), but—given the nature of windborne pollen—with the wind blowing in the right direction during the peak pollination period, it is still quite possible to get a small but significant level of cross-pollination at this distance. That is why these recommendations are only for garden beets with the same root color. Separating red beet crops from other garden beet crops with different-colored roots will require greater isolation distances. Likewise, separating table beets from the other very closely related Beta vulgaris crops—Swiss chard, sugar beet, and mangels—will require even greater isolation distances than what is needed for separation from the different-colored table beets.
Isolation Distances Between Red Beets and Other Color Types: There are now a number of garden beet varieties available with roots that are orange, yellow, and white. There is also the ‘Chioggia’ type, which has concentric rings alternating between red and white in the interior of the root and is popular as a specialty market variety. (The rings of color are actually alternating xylem and phloem tissue.) The minimum isolation of any of these colored variants should be at least 3 mi (4.8 km) from any other different-colored garden beet variety in open terrain. This is the standard isolation distance used by the Willamette Valley Specialty Seed Association between different-colored beets. If sufficient physical barriers do exist on the landscape between seed production fields, then it is possible to grow two different garden beet varieties with a 2 mi (3.2 km) separation between fields.
Isolation for Different Beta vulgaris Crops and Stockseed: In considering the isolation distance necessary to minimize crossing between seed crops of any two of the four different Beta vulgaris crops (garden beet, sugar beet, fodder beet or mangel, and Swiss chard), most seed companies have agreed on 5 mi (8 km). Through experience, seed growers have discovered that this much isolation is indeed necessary to avoid almost all of the unwanted crosses between these crops. Any progeny that results from a cross-pollination between any two of these crops are easy to recognize, as they always have considerable hybrid vigor, are often more stemmy or leafy, and can look like a Swiss chard plant or an excessively large mangel or sugar beet. This is why crosses are so assiduously avoided. If sufficient physical barriers do exist on the landscape between seed production fields, then it is possible to grow two different garden beet varieties with a 3 mi (4.8 km) separation between fields.
Stockseed always requires a higher degree of caution in its production than commercial seed. Beet seed production companies that have maintained high standards of varietal purity in their beet varieties over long periods of time use a minimum 5 mi (8 km) isolation distance for all stockseed increases, without question. This distance is used as an absolute whether in open terrain or with physical barriers present, as genetic mixing in stockseed can be so detrimental to the integrity of the variety (see chapter 17, Stockseed Basics).
Isolation from Genetically Modified Versions of Beta vulgaris: The troubling issue of genetic contamination from genetically modified (GM) crops in certified organically grown seed is discussed at length in chapter 13, Isolation Distances for Maintaining Varietal Integrity. Sugar beets are the first of the B. vulgaris crops to be genetically engineered. A large share of the North American seed production for sugar beet is in Oregon’s Willamette Valley and is owned by three or four large corporate agricultural companies. The independent seed growers producing organic garden beet and Swiss chard seed in the Willamette Valley are faced with GM sugar beets on all sides; even with 5 mi (8 km) isolation, some crossing is inevitable. Isolation distances between GM beet fields and organic seed production fields should probably be at least twice this far, 10 mi (16 km), if there is any hope of preserving the genetic integrity of certified organically grown crops. In all instances it must be remembered that crosses can occur even at these isolation distances, as is true with all crops under any field conditions (see chapter 13, “The Myth of Pure Seed”).
Spinach
Spinach (Spinacia oleracea) is one of the most widely grown vegetables in temperate climates around the world. It is derived from a leafy, winter annual that evolved in and near the Fertile Crescent of the Middle East. Winter annuals are plant species that germinate in the cool of the fall and grow vegetatively until the short days and cold of winter slow their growth. In spring, winter annuals grow steadily until a combination of environmental factors prompts the reproductive phase of the life cycle. Spinach bolting is initiated primarily by daylength, and the ancestral forms of this crop bolt very early in spring with less than 14 hours of light per day. This allowed the predecessor of modern spinach to mature seed before the onset of the intense heat of summer in the Middle East. The seed then lay dormant, having evolved to only germinate with the onset of cool, wet weather in fall, and thus the cycle was repeated.
Modern forms of this crop have been selected to produce a lush and robust leafy vegetable that is widely adapted across environments and seasons. Various types of spinach still produce well as a fall-sown vegetable that can be harvested in fall, winter, or spring. It is easily cold-hardy to 15 to 18°F (–9 to –8°C) but can survive much lower winter temperatures if insulated by snow. Many contemporary varieties have been developed to be spring-planted and produce a bountiful crop before the summer daylength causes bolting. Much recent breeding work has been devoted to develop fast-growing, upright plants that thrive at high population densities and are harvested at a juvenile or baby-leaf stage for bagged salads. Spinach leaf surfaces are smooth, semi-savoyed, or fully savoyed, depending on the amount of leaf curl. The savoyed curl is due to varied rates of growth of ground tissue parenchyma between leaf veins. Leaf shape ranges from the putative older form of triangular blade that is referred to as having an arrowhead or Christmas tree shape, characteristic of Asian spinach varieties, to the rounder, less lobed leaf that has become the ideal in European and North American markets. Selection for color in variable spinach populations has created darker leaf pigmentation. Research investigating the nutritional quality of spinach has found that the dark green types have higher levels of a variety of phytochemicals with antioxidants such as the carotenoid lutein, which is important for the health of the macula in the human retina.
‘Viroflay’ is a classic smooth-leaved spinach variety that is a progenitor of the modern North American fresh-market type.
Crop Characteristics
Spinach is dioecious, with separate male and female plants. In this photo a female plant with immature seed already forming is on the left and a robust vegetative male at peak flowering is on the right.
Reproductive Biology
Spinach is largely dioecious in its flowering habit (see chapter 2, Reproductive Biology of Crop Plants). The number of male plants to female plants is roughly equal in large populations. Occasionally, there may be monoecious plants in a spinach population that express both male and female flowers on the same plant, but these are less common. Male spinach plants exhibit two basic plant forms. The first males to flower are quite short in stature (often only 4 to 6 in/10 to 15 cm tall at full development), with suppressed leaf development on all upper nodes, but prodigious in staminate flowers at all nodes. These extreme males, as they are often called, flower only for a short period of time and die after flowering but are capable of producing large amounts of pollen, ensuring that plenty of pollen is available for early-flowering females. The second type of male plant is known as a vegetative male and is a more robust, larger plant with both staminate flowers and leaves at all nodes. Vegetative males initiate flowering a week to 10 days after the first appearance of extreme males. They are longer-lived than extreme males and flower over a longer duration, ensuring ample pollen for the female plants throughout the period of pollen receptivity. Female plants are similar in stature to vegetative males and bear pistillate flowers and leaves at all nodes. They are long-lived and usually begin flowering within 3 to 7 days of the vegetative males.
A closer view of a female spinach plant (above) and two extreme male plants (below). Photo courtesy of Organic Seed Alliance
Flowering is initiated primarily due to daylength. Heat can play a role by speeding the metabolic rate of the spinach plant, accelerating the flowering process once flowering has been initiated. Spinach is predominantly wind-pollinated and has extremely light pollen that is easily carried long distances by the wind. Both male and female flowers are very small and lack petals. Both types of flowers are borne in groups in the leaf axils of their respective plants. The calyx of the male or staminate flower has a sepal below each of the four stamens. In turn, two anthers are borne on each stamen. In the female, or pistillate flower, the calyx can have two or four sepals that persist after fertilization and combine with the pericarp to create a hard protective casing for the single-seeded fruit. The calyces of several fruits that are borne together can fuse and form tight clusters of seed that will require special seed-cleaning techniques when milling the seed.
The spinach seed coat may be either prickly or smooth. Historically, the prickly-seeded types were generally the large-leaved winter varieties (presumably, the more ancestral form), while the smooth-seeded types were the spring and summer varieties. The prickly-seeded trait is increasingly rare today, and there does not seem to be a genetic association between the prickly seed coat and either winter hardiness or large leaves.
Climatic and
Geographic Suitability
Specific environmental conditions are required to produce high-quality yields of high-germinating, large-seeded spinach crops that are free of seedborne pathogens. Spinach is a cool-season crop that is very sensitive to temperatures above 75°F (24°C), both as a vegetable and as a seed crop. For this reason, there are few locations where spinach seed can be grown for commercial use. The two most important spinach seed production areas worldwide are the Skagit Valley of Washington and a large swath of central Denmark. Both areas have cool, wet springs followed by dry, cool summers (temperatures usually not exceeding 75°F/24°C) and relatively dry fall weather for harvest. The cool, wet spring weather of these ideal climates enables the spinach plant to establish a robust, large vegetative rosette of leaves before flower initiation under the longer days of late spring. Summer weather that exceeds 85°F (29°C), especially during pollination and early seed development, can dramatically lower germination rates, seed size, and seed yields. As is common to all dry-seeded vegetables, an extended dry period in late summer is favored for producing a seed crop that is relatively free of disease and disease-causing inoculum.
Seed Production Practices
Soil and Fertility Requirements
Spinach grown for seed can be planted on a variety of soils, but the soils must be well drained to avoid root rot problems. Soil pH should be maintained above 6.0, as spinach is sensitive to acidic soils. In seed crops, the amount of available nitrogen should not be too high in order to avoid excessive vegetative growth before bolting, as this promotes lodging of the plants during seed set. Well-maintained agricultural soils that are high in humus and microbial populations will supply adequate nutrients and water over the long seed production season. Spinach is somewhat tolerant of soil salinity and very tolerant of alkaline soils, although foliar fertilizer applications may be needed on alkaline soils to counteract the reduction in availability of micronutrients such as manganese under high soil pH.
Growing the Seed Crop
The optimum temperature range for germination of spinach seed is 45 to 75°F (7 to 24°C). Spring-sown spinach can be planted as early as the ground can be worked, though waiting another week or two till true spring weather prevails to plant will ensure vigorous seedling growth. Planting should not be delayed too long, however, as the key is to get as large a vegetative rosette as possible before flower initiation. This rosette of leaves (or frame, in the parlance of seed growers) will not grow appreciably after the flower stalk emerges and will be the photosynthetic factory responsible for producing the seed crop.
Sometimes spinach seed crops are planted in late summer or fall and overwintered for seed production the following summer. This eliminates ground prep and planting during inclement spring weather. It also enables the spinach to develop a larger vegetative frame to optimize the seed yield potential of the crop. Unfortunately, the overwintered crop may act as a green bridge, providing a live, vegetative host allowing a number of diseases to survive through the winter (see chapter 16, Seedborne Diseases).
The planting density for spinach seed production requires much wider spacing than for producing spinach as a vegetable. For seed production, spinach plants are generally spaced 8 to 12 in (20 to 30 cm) apart within rows. Standard row centers are normally 22 to 26 in (56 to 66 cm) apart, but in raised beds spacing between rows can be dropped to 12 to 14 in (30 to 36 cm) apart. Wider plant spacing increases airflow through the crop, reducing disease pressure. Spinach seed crops are still often grown with overhead irrigation in the Pacific Northwest, although its use is limited to the early part of the season before bolting, flowering, and seed maturity. Avoid it during these reproductive phases of the life cycle, as the incidence of foliar and possible seedborne diseases will certainly increase as a result. Drip or furrow irrigation has the advantage of not wetting the foliage and can be used throughout the season.
Early-season weed control is critical for optimum establishment. If plants become leggy due to early competition they will be difficult to evaluate in the selection process and be more prone to lodging when full-sized. Spinach seedlings grow slowly and do not compete well with weeds. Starting with a stale seedbed is advisable, as well as avoiding fields with high weed pressure. Pre-emergence flame weeding can be effective. Thinning and blocking by hand are usually required in organic production, as is hand hoeing until plants are large enough to not be smothered by mechanical cultivation.
The fact that spinach is dioecious is an advantage in hybrid spinach seed production. The female plants can be used to develop all female flowering lines. This is possible because female spinach plants, if isolated from spinach pollen during flowering, will eventually “sex reverse,” subsequently producing male flowers in addition to their female flowers in order to achieve pollination. The subsequent generation will inherit the female genes. This sex reversal enables breeders to increase seed of a female line. During the development of female lines for hybrids, the breeder must perform meticulous selection on the female plants, ensuring that the lines uniformly produce only female flowers for at least 5 to 6 weeks before sex reversing. Then, when used as female parents in hybrid seed production, these lines will have adequate time to receive all of their pollen from the male parental line of the hybrid in the field. Female plants can also be selected to have a monoecious flowering habit to serve as the male parent. This eliminates the variability of having both extreme males and vegetative males as your male pollen source and produces much better phenotypic uniformity in the resultant vegetable crop, especially as it just begins to bolt (when spinach is often still harvested). All of this can be done without resorting to chemical growth regulators and is therefore possible in organic production systems.
Seed Harvest
Spinach seed maturing on the plant.
Spinach seed, as with all members of the Amaranthaceae, is formed and matures in an indeterminate growth pattern, beginning on older, lower branches and continuing up the flower stalk through the season. Due to this sequential maturation, only a portion of the seed continuously being set will reach maturity by the end of the season. In most cases only about 75% of the seed on any given plant will reach maturity by harvest. One of the most difficult steps in successfully growing a spinach seed crop is judging when this optimum amount of seed is mature on a majority of plants in the field. A standard method of gauging the maturity of a spinach seed crop is to make a visual assessment of the percentage of seed on most of the plants that has turned a tan-brown color, typical of mature spinach seed, and then harvesting the crop when 60 to 80% of the seed has become this color. This is an unreliable method of judging maturity, however, due to the considerable effects of genetic and environmental variation. Environmentally, the seed may prematurely lighten in color in the presence of the Stemphylium/Cladosporium leaf spot disease complex (see the table in chapter 16, Seedborne Diseases). Genetically, some spinach cultivars have much greener seed, even at full seed maturity.
The most important trait to monitor in gauging the maturation of spinach seed is the relative maturity of the seed endosperm. The endosperm and embryo, which mature concurrently, must be fully developed to produce vigorous, vital seed. The endosperm, which is primarily composed of starch, is easily monitored by cracking open the seed and squeezing it to visually inspect the stage of endosperm development. Appearance of the endosperm will transition from translucent or milky early in development to what is described as flinty, with a grayish, waxy appearance at the midpoint of development. At these stages, the endosperm can be squeezed out of the developing seed for inspection. When seed in the middle of the stalk is at the flinty stage, irrigation may be stopped to speed the maturation and drying process. This can be important if there is risk of maturation extending into the wet, disease-promoting conditions of fall.
At a mature stage of development, the endosperm turns a starchy white color, which can be observed by cracking open the seed. Once the endosperm turns to this solid, true white color and is firm, the seed is mature and ready to harvest. When the majority of the plants in the field have about 75% of the seed at this advanced, starchy white stage, it is time to cut the plants near the base of the stems to stack into windrows. This should be done preferably during a warm, dry period. The windrowed stalks will be ready to thresh in 4 to 10 days, depending on the weather. Rotating stalks in the windrows facilitates uniform drying of the seed. Cutting or windrowing the crop in wet weather should be avoided. If a crop is ready to cut and an extended wet weather pattern is forecast, cut the crop and bring it into an airy, dry shelter to cure. Once dried, seed stalks are usually threshed and then cleaned by screening and fanning.
Threshing is best accomplished with a belt thresher to break up the clusters of seed that form when the calyces of several spinach fruits fuse while maturing. Many seed companies then clean away any remnant of this fused material, as well as prominent burrs in prickly-seeded types, with a rotary deburrer in a process that approximates decortication in beets and chard.
Genetic Maintenance
When planting spinach with the intent of performing selection on a population, the initial planting density that I use is anywhere from six to eight plants per foot (30 cm) within the row.
Planting six to eight spinach plants per foot (30 cm) for the initial stand before practicing selection establishes a population that is large enough to perform multiple selection events from the time of emergence to flower initiation and ensures that you will still have an adequate population to maximize your seed yield at the end.
As with all crops, seedling vigor and early robust growth are always important traits to select for in organic production systems. Spinach prospers from increased vigor as the spring crop is often planted into cold, wet soils and must make rapid growth before longer daylength and hot weather induce bolting. Selecting for vigor may be accomplished by eliminating any slower, poorly formed seedlings after all (or most) of the seedlings have emerged. This can be repeated in another 7 to 10 days, eliminating any slowpokes or malformed plants.
Matthew Dillon, the author, and Micaela Colley evaluate spinach varieties in a field trial.
There are various stages at which leaf size can be selected depending on the leaf shape desired by the vegetable market you serve. As an example, much of the modern baby-leaf and teenager-leaf spinach is selected for rounded leaves. Alternately, some prefer the triangular or arrowhead-shaped (also called Christmas tree) spinach leaf for shape variation in prepared salad mixes. Leaf textures are characterized as savoyed (extreme leaf curl), semi-savoyed, or flat, and are very important in determining the market class of spinach varieties. Open-pollinated spinach varieties can have considerable plant-to-plant variation in their degree of savoy curl, and it is important to select for uniformity of this trait. Anyone selecting for this trait should also realize that the degree of curl varies with the stage of growth and seasonal temperatures. Likewise, variation in leaf color is common in open-pollinated spinach populations, and gain from selection is possible. Darker leaf color is usually preferred and is correlated to higher levels of nutritionally significant carotenoids. Selection for color can be done across growth stages.
Plant stature is another important trait for spinach growers, especially for harvest of leaves cut for salad mix. The ability of the plant to hold its leaves in an upright position can reduce the amount of soil that may get trapped in the underside of leaves. Upright foliage also lessens the amount of fungal and bacterial pathogens that can be splashed onto leaves due to rain or irrigation.
Incidence of disease should be monitored and identified accurately for proper field management and for selection purposes. Routinely selecting for plants free of disease or with relatively low incidence of disease symptoms can help develop partial or horizontal resistance to a particular pathogen. This requires familiarity with the symptoms of spinach diseases endemic to your region.
Isolation Distances
Spinach, like all of the chenopod crops, has pollen that is known for its ability to travel great distances. It is almost exclusively wind-pollinated, and its pollen is relatively small, light, and easily carried by the wind. The male plants of this dioecious crop will usually produce so much pollen that it is possible to see yellow puffs of it moving across a spinach field with a gust of wind at the peak of pollination. Depending on the direction and force of prevailing winds and the relative humidity, spinach pollen can pollinate other flowering spinach crops within 2 mi (3.2 km) if grown in open terrain. While this may represent a rather small amount of outcrossing to another spinach crop at this distance, it is especially important when the two adjacent crops are distinctly different types of spinach or are foundation seed or stockseed, where purity is very important.
If a substantial physical barrier is present (see chapter 13, Isolation Distances for Maintaining Varietal Integrity), then the minimum isolation distance needed between two different spinach crops can be lowered to 1 mi (1.6 km). However, it should always be remembered that these isolation distances are not absolute, and there may still be a small amount of crossing even at these higher isolation distances, especially with wind-pollinated chenopods.
Swiss Chard
Swiss chard is one of the four crops shared by the species Beta vulgaris and is probably closest to the ancestral form of this species that grew wild in the Mediterranean Basin. A number of researchers agree that the earliest cultivated beet-like vegetable was probably grown for its leaves. Continued selection for larger, more succulent leaves resulted in the crop that is usually called either Swiss chard or silver beet. As this progenitor crop also had a substantial root (something typical of many biennials), there were farmers that selected it for a more refined, fleshy, edible root, which became both the table beet and mangel.
Chard’s common name is a corruption of the Old French cardon, for “cardoon,” a similar-looking but unrelated vegetable (Cynara cardunculus, a close relative of globe artichoke) with origins in the Mediterranean region. Chard, like cardoon, has long been prized for its succulent, celery-like thick stalks or petioles. The Swiss part of its moniker is also inaccurate, as the crop’s origins are definitely farther south and probably from coastal areas of the Mediterranean. Chard’s modern association with Switzerland is mired in mystery, although there does appear to be evidence that there was a preference for it in Switzerland over some other leafy greens more popular in other parts of Europe.
Chard’s popularity is growing thanks to the expanding market for fresh, local produce. It is also now widely used as a component of salad mixes of all kinds. Chard is now frequently planted thickly and cut as a baby leaf for bagged salad mixes. This has raised its profile as a vegetable crop, and there has been a flurry of plant breeding to create the various-colored chards that have entered the market in recent years. A number of new colors in the stems of Swiss chard have been added to the more traditional colors of red and white. While yellow pigmentation has long existed as a color in B. vulgaris crops, the number of newer varieties with shades of yellow and gold has skyrocketed. Yellow and gold are complemented with other shades of chard, including pink, magenta, orange, and intermediate hues of these as well. A number of seed companies have also designed multicolored mixes with many or all of these colors, which have become popular in many markets across North America.
Crop Characteristics
Reproductive Biology
The reproductive biology of Swiss chard is virtually identical to that of the garden beet, as they are the same species. The only noticeable morphological difference is that chard’s flowers are borne on internodes that are usually spaced farther apart than the flowers borne on most beet varieties.
Climatic and
Geographic Suitability
Swiss chard seed is grown in many of the same regions that are ideally suited to beet seed production (see Garden Beet). However, chard seed is sometimes grown in districts with summer high temperatures that can be as much as 6 to 10°F (3 to 6°C) warmer than what is normally advised for beet seed production. Chard seems to thrive at these higher temperatures, and some growers believe that the extra heat units gained by growing chard in these warmer districts may contribute to increased seed yields at season’s end.
Seed Production Practices
Soil and Fertility Requirements
Swiss chard prefers the same soil and fertility regimen as beets.
Growing the Seed Crop
Growing the chard seed crop is virtually identical to growing the beet seed (see Garden Beet, “Growing the Seed Crop”). There are only a couple of small variations in the manner of how you treat the chard seed crop, which are discussed below.
Many chard varieties can achieve a much larger overall size and stature (height and width) when flowering and producing seed than is normally achieved for a beet plant during the reproductive phase. Some chard varieties can easily achieve a height of 6 to 7 ft (1.8 to 2.1 m) or more. Chard roots can be described as unrefined beet roots. They probably look much like the roots of the ancestral biennial plant from which the modern table beet is derived. Chard roots may have multiple growing points on the taproot and many adventitious roots coming from the root area adjoining the taproot. The root crown is often larger and more irregularly shaped than the crown of the more refined beet. Both of these features make chard roots somewhat more susceptible to rotting when stored in coolers or root cellars, especially in the high-humidity conditions that root storage requires. Fortunately, if stored properly (see chapter 3, Understanding Biennial Seed Crops, “Overwintering the Crop”), chard roots can have just as good a survival rate as beets.
When chard roots are overwintered in the field for seed production, they can be somewhat more cold-hardy than beets in mild temperate climates. Like beets, the growing point of a chard plant will become damaged during winter in many temperate climates. Some garden beet varieties will suffer permanent damage to their growing point and not resume growth in spring when exposed to temperatures of approximately 25°F (–4°C) and below. In contrast, I have witnessed a number of chard varieties where a percentage of the plants will survive temperatures down to 14°F (–10°C) if they are not subjected to long periods of time at these temperatures, or where cold weather of this intensity doesn’t recur multiple times throughout the winter. The recurring freeze–thaw syndrome at these temperatures can be very hard on plants that might otherwise survive a couple of skirmishes at these lows. Some of the methods used to cover a standing root crop with a straw or soil mulch may also prove beneficial in this situation (see chapter 3, “Preparing Roots for Storage”).
Seed Harvest and
Seed Cleaning
Seed harvest and seed cleaning for chard is practically identical to the process for beet seed. The only possible difference would be the fact that the second-year chard plant is usually significantly larger than the second-year beet plant, and therefore, when piling the plants into windrows, you must be careful to pile the plants in short enough piles that they will still dry quickly in the field.
Genetic Maintenance
Genetic differences within a chard variety are apparent at multiple stages in the crop’s life cycle. Upon sowing the crop, you have an opportunity to select for seedling vigor as the crop emerges from the soil. Within the first few days after the emergence of the seedlings, it is usually quite easy to select against the seedlings that are later emerging and obviously less vigorous. At this stage it is also quite easy to identify seedlings that are not true to type for petiole or stem color. The common white or pale green petioles are recessive in their expression to all of the other colors: red, magenta, pink, orange, yellow, and gold. Seedlings resulting from crosses between the deeper colors and the white and pale green types can be expressed as intermediate pale colors. It is easy to thin out the white, light green, and pale intermediate segregants in the seedling stage. Expression of the petiole color in the seedling stage is relative and has a strong correlation to the degree of pigmentation in the adult plant. Hence, any selection for intensity of petiole color at any stage in chard’s vegetative growth will increase the color for use of the crop as either a baby leaf or bunching variety.
Any of the intensely pigmented Swiss chard varieties like this golden type require selection during seed production to maintain good color.
Selection for the intensity of the green leaf color is also important, as chard’s ground or underlying leaf color can range from very pale green to a deep forest green. Most farmers marketing the crop agree that a darker green, especially in contrast with a rich petiole color, is very attractive in the marketplace. Likewise, maintaining a solid green color into the cooler weather of fall, when the leaves of many chard varieties start to turn a rusty brown or chocolaty color, is considered important by many growers. While colder temperatures trigger this change in color, there is almost always genetic variation within different chard varieties, allowing room for selection toward greener plants.
Considerable variation also exists in many chard varieties for the width of the petiole. Many European white-stemmed types that are exported around the world have very wide petioles. This is also true of varieties from Australia, New Zealand, and South Africa. Little or no selection for petiole width has been practiced on most North American types, and genetic variation for petiole width is almost always present. Because growers that are bunching their crop usually prefer wider petioles, it is an obvious trait to select for as when producing a seed crop.
Foliar diseases are usually not severe but are often present in most temperate climates. Cercospera leaf spot (Cercospera beticola) and phoma (Phoma beta) can be found in many districts where chard is grown, and there is often plant-to-plant variation for symptoms for both of these leaf-spotting diseases. Breeders have been successful incorporating partial resistance to both of these maladies by carefully selecting over generations for plants with less severe symptoms. Downy mildew (Peronospera farinosa) also affects chard in much the same way it affects beets (see the Garden Beet section). Much like beets, chard roots coming out of storage can have a grayish growth, typical of latent downy mildew, on the crown and growing point, which can later affect the flowering structures and seed yield. Selection has been successful in developing good levels of partial resistance in both beets and chard.
Isolation Distances
Isolation distances are the same as with beets, with similar increases in distance between colors. Increased isolation distances must also be used between chard and the other crops of Beta vulgaris: beets, mangels, and sugar beets (see Garden Beet, “Isolation Distances”).