The Asteraceae is the largest family of flowering plants in the world. It includes over 1,500 genera and more than 23,000 species of woody and herbaceous plants. Considering the size of this family there are relatively few vegetable crops of major importance, specifically lettuce (Lactuca sativa), endive (Cichorium endivia), and the chicories (C. intybus). This family also includes sunflower, however, which is one of the five most important oilseed crops worldwide, and globe artichoke, which does not come true from seed and is usually propagated asexually. The Asteraceae also includes the minor vegetable crops burdock root, cardoon, Jerusalem artichoke, salsify, and scorzonera.
The Asteraceae are dry-seeded crops, and their seed is most successfully grown with little or no precipitation during the flowering and seed maturation process (see “Cool-Season Dry-Seeded Crops”). Almost all commercial seed of lettuce, endive, and the chicories is grown in temperate regions with dry summers and moderate temperatures, the so-called Mediterranean climate. However, small, localized seed production of regionally important varieties does occur with both the major and minor crops of this family. Decentralized seed production is quite common in types of chicory crops like radicchio and catalogna in parts of Southern Europe, where many farmers still maintain their own varieties with a healthy amount of variation and a high degree of adaptation to the local environment. In radicchio these farmer-bred varieties are prized and are often quite unique to a region.
Family Characteristics
A lettuce capitulum appears to be a single flower, but is actually a cluster of florets.
All species within this family have flowers borne in head-like flower clusters. Each head, called a capitulum, appears to be a single flower but contains a group of single florets that are protected by a whorl of bracts, called an involucre. Lettuce, endive, and the various chicories are all members of the tribe Lactuceae and have florets with five fused petals and five fused anthers that form a column surrounding the pistil. A branching, corymb-type, racemose inflorescence will blossom indefinitely in all three of these species, usually until the end of the season in most temperate climates. Seed will mature sequentially, and—as in the case of lettuce—the seed is sometimes harvested multiple times during the season to optimize yield and quality.
Lettuce flowers are borne in a corymb-like flower cluster, in which flower stalks along the stem of the plant all grow up to approximately the same height.
Life Cycle
Lettuce and endive are annuals and can produce a seed crop in a single season. As with most annual seed crops, it is crucial to produce a vigorous frame of vegetative growth during spring to support a healthy, fully realized flowering plant in summer. These stages must happen in a timely fashion in an appropriate climate to produce an adequate yield of fully mature seed.
Some regions with appropriate climates in all other regards may simply have too short a growing season for some of the varieties of these annual species to mature sufficiently and make a good seed crop. Also, in both lettuce and endive there are varietal differences in the number of days it takes to mature a seed crop. Certainly, many lettuce and endive seed growers will stress how important it is to get these crops started and growing in the field as early as possible to realize a good yield. In most temperate climates appropriate for the production of seed of these crops, it is important to first test all prospective seed crop varieties of these annual Asteraceae species in a small suitability test plot before committing a larger field to commercial seed production of a variety that may not mature in your region. While the indeterminate nature of the flowering in these crops means that you will never harvest the full complement of seed from any Asteraceae crop, you should expect to harvest at least 60 to 70% of the seed that matures on a fully flowering plant if the crop is to prove commercially viable in your particular environment.
The chicories (Cichorium intybus) are essentially biennials, requiring a period of vernalization, or cold treatment, to promote flowering (see chapter 3, Understanding Biennial Seed Crops).There are great differences in the vernalization requirement between different chicory crops and within the varieties of each crop type. When produced as vegetables there is always the danger of any of these crops bolting during the first season if planted early in the season, when there are plenty of cool nights with temperatures that routinely fall below 50°F (10°C). For seed production these crops should be planted or transplanted in midsummer when danger of premature bolting has passed. They will then produce a reserve of energy in their roots, petioles, and leaves, which is stored for winter and used in the next season after flower initiation for production of seed.
Climatic Adaptation
These three species of the Asteraceae are indigenous to the greater Mediterranean Basin and Middle East area. The ancestral form of lettuce most probably had a very short vegetative phase in early spring and flowered long before the onset of high temperatures in summer. The early forms of endive were probably winter annuals, producing a vegetative frame during the cool winter months and also completing their reproductive phase before the heat of summer. The biennial ancestors of the chicories took advantage of the mild winters in the area and put on most of their growth during the cool of winter, also flowering early enough to produce seed before the hottest part of the summer. The modern-day forms of these crops produce inferior seed in hot weather that exceeds 86°F (30°C), although some fluctuation above this can occur in later stages of development (after initial seed set and early rapid growth of the seed), if it is not excessive and sustained. These crops all excel in temperate climates with dry, warm summers and falls, mild winters, and cool, moist springs that encourage luxuriant foliar growth.
Seed production for these three species is generally best accomplished in warm temperate zones that are warmer than the cool coastal regions where the cool-season crops are grown, and they usually require a longer season to mature a full seed crop than many cool-season crops (see chapter 15, Seed Crop Climates).
Seed Harvest
Because the seed of lettuce, endive, and the chicories is borne on plants with indeterminate flowering, it is important to remember that the seed crop for all of these species does not mature uniformly. Hence, they are all harvested when approximately 50 to 70% of their seedheads are mature, depending on the species, specific variety, and environment in which they are produced. Seed growers must be attentive to harvesting the seed when there is an optimum amount of mature seed before the first seed to set (which can often be the highest-quality seed of the lot) starts to shatter and is lost.
A lettuce seed field.
When the plants of these species have reached a maximum maturity they are usually cut and windrowed in the field, allowing the crop to dry and further mature in the sun. Threshing follows several days later, by either manual or mechanical means. Some seed growers avoid mechanical threshing, as immature seed (which isn’t easily released from immature seedheads when the crop is threshed manually) will be mixed in with the fully mature seed using mechanical methods. Since much of this immature seed can be the same size and nearly the same weight as the mature seed, it is not easily separated from the mature seed in the cleaning process. This can mean the difference between a seed lot that germinates in the 80 to 90% range and one that germinates well into the 90s.
Mechanical harvesting of lettuce seed in one step is sometimes used in larger seed production operations. It is possible to combine the standing crop directly from the field if the crop is sufficiently dry. However, this method has two inherent flaws in the production of high-quality commercial seed. First, there can be considerable waste through shattering when the crop is cut by the moving combine. Second, this method bypasses the curing of the seed in a windrow that is usually done, as a significant fraction of “almost mature” seed at the initial time of harvest will mature during the curing process.
Seed Cleaning
Asteraceae seed should be spread out and dried quickly after harvest, as small pieces of stems, leaves, and flower parts can hold a significant amount of moisture in the threshed material. This should be done in a shaded area, since direct sun (and heat) can cause dormancy in these species.
The bulk of the cleaning is accomplished through some form of winnowing that can easily remove the lighter plant debris from the seed. Slotted screens are also useful for removing immature flower buds. A gravity table can be used to separate the light, less mature seed from the good seed.
Genetic Maintenance
Both lettuce and endive are self-pollinated species, so they are easily maintained as true breeding for most traits with simple roguing. The chicory crops are cross-pollinated and therefore require considerable attention to ensure that their inherent variability remains within the range that the producer deems allowable for that particular crop (see chapter 13, Isolation Distances for Maintaining Varietal Integrity).
The traits that are important for selection in all of these leafy crops include leaf shape, texture, color, color variation, and plant stature. Also universally important is selection for resistance to tipburn, premature bolting, lettuce mosaic virus (LMV), aster yellows, and sclerotinia (Sclerotinia sclerotiorum). The presence of sclerotinia in seed crops of these three species is quite prevalent and can be destructive. Several organic seed producers in the western United States have made considerable progress increasing the level of resistance in a number of lettuce varieties through selection for horizontal resistance (HR) to this fungal pathogen. Significant levels of resistance to tipburn and premature bolting, as well as HR for LMV, have also been achieved through careful selection during genetic maintenance of lettuce stocks. Consideration of leaf thickness, waxiness, and presence and degree of leaf pubescence are also traits to be monitored in the selection, especially in the chicories.
Isolation Distances
The isolation distances for the self-pollinated crops in this family, lettuce and chicory, are frequently debated, as crossing can occur between different varieties in each of these two species. Recommended isolation for growing two lettuce varieties will usually specify a minimum of 6 to 12 ft (1.8 to 3.7 m) between varieties or whatever distance is necessary to avoid physical mixing of plant material at harvest. Endive’s is often less specific, stating that it is “similar to lettuce.” As with all cases of potential cross-pollination in self-pollinated species, the incidence of crossing will go up in certain environments and when the crop is grown organically, depending on the type of pollinators present (see chapter 13, Isolation Distances for Maintaining Varietal Integrity). While lettuce and endive growers in many climates report very little crossing at the standard isolation distances of 6 to 12 ft (1.8 to 3.7 m) between varieties, this is not recommended as standard practice, since some percentage of crossing (usually well below 1%) can occur in almost any climate and will probably be higher than that in some climates.
Chicory
The name chicory distinguishes two types of crops belonging to the species Cichorium intybus L. The first type, the salad chicories, are all used as leafy vegetables and are classified into four major crop groups: (1) radicchio (Chioggia, Treviso, and Castelfranco types); (2) pain de sucre (sugarloaf chicory); (3) witloof chicory (Belgian endive); and (4) catalogna (Italian dandelion or asparagus chicory). The second type of chicory is known as root chicory, which produces a large fleshy root that is ground, roasted, and mixed with coffee. The salad chicories are grown to some extent in all temperate regions around the globe, producing their most favorable crops when their culture includes some seasonal cool conditions. Both the salad chicories and chicory root are biennials, requiring a cold vernalization to produce flowers and subsequent seed.
The probable center of origin of this species stretches from the northern reaches of the Middle East to the southern Balkan Peninsula, from whence it eventually moved throughout the Mediterranean basin and northward across Europe. Over time and through selection in diverse agricultural settlements there developed a diversity of forms, giving us the rich number of forms within and across the four major crop types. With the spread of this species also came the spread of the wild form of Cichorium intybus, often just called wild chicory in English, which is a major weed of fencerows and roadsides in any number of temperate regions around the world.
Ethnobotanists speculate that pain de sucre, a rustic leafy crop that resembles romaine lettuce and is sometimes called sugarloaf chicory in English, may be the oldest cultivated vegetable in this species, though its cultivation is largely confined to the border regions of Southern Europe where France, Switzerland, and Italy meet. The first cultivation of radicchio, a group of chicories with red leaf pigmentation, may derive from the ‘Rossa di Treviso’ types grown in northern Italy in the 15th century. Different radicchio cultivar groups may have been derived from these types, including early- and late-maturing Treviso types, round red Chioggia types, and the largely green-leaved, Castelfranco types that are variegated with red spots.
‘Catalogna a Foglie Frastagliata’ is a Catalogna-type chicory, commonly known as “Italian dandelion” in North America for its deeply indented leaves and upright growth habit.
Although it is still a mainstay of Italian cuisine, chicory’s use has spread across Europe and beyond. There is speculation that the enlarged apical bud that is witloof chicory (commonly called Belgian endive in English) was first selected by Belgian farmers from overwintered chicory roots stored in pits for roasting in the 1870s. The tender white leaves from these blanched yellowish leaf buds that had enlarged during winter slowly became popular in Belgium as farmer breeders developed varieties that would consistently produce tight buds that suited the burgeoning demand for this off-season leafy crop. Catalogna is probably of Italian origin. In English it has historically been called asparagus chicory, but as its leaf shape is reminiscent of dandelion, it is often sold under the name Italian dandelion in North America.
These various leafy chicory crops are most widely grown in Europe, but with a few exceptions they have not gained wide acceptance in the rest of the world, occupying a specialty market status. The most notable exception to this has been the increase in use of radicchio and catalogna in cool-season premixed salads in industrial societies over the last decade.
Most of the world’s chicory seed is produced in Europe, with France and Italy the most important production areas. There is also production of some of the hybrid witloof and radicchio seed in other parts of Europe. All of these crops require a vernalization period for flowering. The open-pollinated types are usually overwintered in the field in milder climatic zones to satisfy their vernalization requirement, whereas the parental stocks for hybrid production are often stored in controlled environments between the first and second seasons of their biennial life cycle and therefore have a wider geographic range for seed production.
Crop Characteristics
Reproductive Biology
The morphology of all reproductive parts of chicory (C. intybus) is very similar to that described for endive (C. endivia) (see Endive & Escarole, “Reproductive Biology”), although there can be slight differences in length of the peduncles (flower-bearing axillary shoots) and in the number of flowers borne in each capitulum. The endives also seem to physically close their flower clusters earlier in the day than the chicories. Otherwise, the emergence of the stigma through the channel formed by the anthers is very similar to endive at anthesis. The bottom line is that the two species are sexually compatible with each other and therefore must be treated as if they were the same species, respecting isolation distances when producing seed of any member of the genus Cichorium (see “Isolation Distances”).
The main reproductive difference between these two species is that C. endivia is highly self-fertile, and very little crossing between plants takes place, whereas C. intybus has a very strong sporophytic incompatibility, which limits self-fertilization to far less than 1% of opportunities to self under field conditions. In other words, endive seed is almost always the result of self-pollination, while chicory requires cross-pollination in order to produce seed, as an individual chicory plant will not receive its own pollen. Because the chicories must receive pollen from other individuals, they are much more apt to outcross than endive. For this reason the chicories must be isolated farther from endive than the reverse (see “Isolation Distances”).
The second major difference between chicory and endive is their life cycle. The various endives are all annuals, while the chicories are biennial and may initiate flowering after some combination of vernalization and the lengthening hours of daylight in late spring. The vernalization requirement in chicory can vary widely, and certain crops and cultivars within C. intybus will often run to seed by midsummer if they are exposed to temperatures at or below 50°F (10°C) for extended periods of time during early stages of growth. As annuals, all endive crop types (C. endivia) will readily flower during their first season of growth, regardless of environmental conditions.
R_fmt.jpg)
Chicory flowers (Cichorium intybus) from a Castelfranco type (left) and from a radicchio (right).
Climatic and
Geographic Suitability
The crops of the Cichorium genus are quite cold-hardy, easily overwintering in most parts of their center of origin (Mediterranean basin and southwestern Asia). There is ample genetic variability for tolerance to cold between crop types and specific varieties among the chicories, making them ideal for overwintering in many of the more moderate climatic regions of the temperate zone. Most chicories will come through winter temperatures between 20 and 25°F (–7 and –4°C) with little damage, especially if they are at a relatively early stage of growth. I have seen several different radicchio varieties with young plants bearing 8 to 10 sets of true leaves that had a greater than 50% survival rate when the winter low temperature reached 15°F (–9°C), without any thermal protection or snow cover.
Like endive, the chicories are best suited to temperatures between 58 and 68°F (14 to 20°C) for optimal vegetative growth. During the reproductive phases of flowering and seed growth they flourish at higher temperatures, but temperatures shouldn’t regularly exceed 86°F (30°C) for high-quality seed. Cool springs that encourage good vegetative growth followed by seasonally dry summer weather are desirable in order to attain adequate yields and harvest clean, disease-free seed. The growing season is somewhat longer than that needed for many of the cool-season brassica and chenopod seed crops. Much of the commercial seed crop is produced in the Netherlands, Belgium, northern France, and northern Italy. The eastern part of the Po River Valley in Italy is an important seed production region, especially in the regions of Emilia-Romagna and the Marche. In fact, at the time of this writing, there are still many farmers in these regions that maintain open-pollinated family strains. In North America the Willamette Valley of Oregon and a number of interior valleys of Northern California have proven to be well suited to producing high yields of high-quality chicory seed.
Seed Production Practices
Soil and Fertility Requirements
Chicories can be grown on a wide range of soils for seed production; however, soils must be well drained to minimize the chances of a number of diseases becoming a problem. Chicory does well on lighter sandy or silt loams as a vegetable crop. The plants have rather shallow lateral feeder roots and require a steady supply of water and nutrients throughout the season. When growing chicory as a seed crop many growers prefer somewhat heavier soils, like a clay loam or silty clay loam that can more easily deliver nutrients and water to the crop over the course of the much longer season that is required to produce seed. These soils can be especially important for their ability to hold water during hot weather in late summer as the chicory seed crop is maturing.
Adequate soil fertility that is sufficient to produce vigorous spring growth to establish a good frame or basal rosette of leaves to support a bountiful seed crop is mandatory. Soils rich in available phosphorus are desirable, since phosphorus is essential for early plant development. This is especially important in areas with cool springs, as the mineralization of phosphorus in soils that are managed organically is slow in cool weather. Nitrogen levels should be moderate, as excessive foliar growth can be detrimental to producing a stout and sturdy flowering plant that produces a satisfactory seed yield.
Unlike their close relatives endive and escarole (C. endivia), the chicories (C. intybus) are all true biennials and must be overwintered at temperatures at or below 50°F (10°C). With the exception of the witloof chicory and hybrid radicchio produced in Northern Europe, the chicories are overwintered in the field. As most chicories will easily withstand temperatures between 20 and 23°F (–7 and –5°C) and often colder, with little damage at the peak of the winter cold, they have a somewhat greater geographic range for seed production than many other biennial crops.
In the first year of the 2-year cycle for seed production it is important to determine what the best size is for overwintering the particular chicory type and variety that you intend to grow in your climate. Many of the chicories that form heads, such as the radicchios and pain de sucre types, are more cold-hardy before they have formed a full head. It is important to get these and other chicories large enough in fall so that they will be able to form a substantial frame of a plant in spring, yet not too large going into winter to suffer undo freezing damage. This size depends on both the variety and the environment, and seed growers in colder winter areas will have to experiment in their own environment with the different varieties to find which chicory type or variety is able to successfully overwinter and produce seed.
Generally the chicories are sown into flats 3 to 5 weeks before the date when they will be transplanted into the field in mid- to late summer. Plants can start to be selected for color, leaf type, and vigor when they have four to six true leaves. Seedlings are planted 14 to 20 in (36 to 51 cm) apart within the row depending on the size of the flowering plant, which can vary considerably. Spacing is between 24 and 36 in (61 to 91 cm) between rows.
Seed Harvest
Seed harvest for the chicories is done successfully much like the single harvest method described for lettuce (see Lettuce, “Seed Harvest”). The chicories, however, require somewhat more heat and a longer season to mature their seed than is needed for many of the lettuce varieties. As with lettuce, the seed of the chicories can easily shatter if the capitula are ripe and excessively dry at the time of the pulling of the plants, the laying into windrows, or the final threshing. For this reason it is important to closely monitor the maturation of these seed capsules and pull the plants at exactly the right time.
Genetic Maintenance
Selection for the maintenance or improvement of several key characteristics can be done at different stages in the various chicory crops. This is based on selecting for: (1) horticultural characteristics, including form, shape, color, or flavor; (2) agronomic traits such as growth rate, maturity, or disease resistance; and (3) the plant’s suitability to the seasons of production. As with all leafy green vegetable crops, it is possible to select at various stages of the growth cycle for color, leaf shape, leaf curl, and overall vigor of the plant. This is especially true among the open-pollinated radicchio types, pain de sucre, and catalogna types, which are often still quite genetically variable for both the horticultural and agronomic traits listed above. This makes sense in that these types come from a large and very diverse genetic pool in and near their ancestral center of diversity—the Mediterranean basin. On the other hand, the witloof or Belgian endive types were derived from a much narrower genetic base, as this species was transported to Northern Europe. Indeed, this latter type has been intensively selected and is most often sold commercially as hybrid varieties.
Selection for the color, degree of variegation of leaves, and sometimes flavor can be done early in the life cycle once you learn what constitutes the typical version of these traits for any particular variety. The most successful selection for form and shape of heading versions of chicory crops is done when the crops have formed heads. Flavor can be strongly influenced by temperature or by challenges of the environment.
This species also has a remarkable ability to put on vigorous growth during cool conditions when temperatures don’t exceed 65°F (18°C), even putting on growth at or below 55°F (13°C). Because chicory is a biennial that is often overwintered in the open in the field (with the exception of witloof types), most seed crops will easily withstand temperatures between 20 and 23°F (–7 and –5°C) with little damage at the peak of the winter cold (see “Growing the Seed Crop”). In some cases, based on the size and stage of development, there are some varieties among the different chicory crop types that can survive temperatures down to 14°F (–10°C) in the open field. Depending on the specific crop type and variety it is possible to select for increased cold tolerance at winter temperatures between 14 and 20°F (–10 to –7°C), through a combination of natural selection (plants with apical buds destroyed) and conscious selection (plants that you eliminate due to worse-than-average frost damage), thereby increasing the survivability of the crop in a cold climate over a number of cycles.
As with all biennial vegetable crops there is almost always new vegetative growth in the spring to support the coming reproductive growth of the second year. Many growers have noted the great variation in the vigor, rate of growth, and extent of growth that occurs from one chicory variety to another at this point. This makes it possible to select for the most vigorous or bountiful types at this point in the season; this has obvious advantages to a vegetable grower who is harvesting an early-spring crop, but this additional growth will also give the seed grower an improved frame for the seed-producing plant that can increase the potential seed yield.
The first hurdle you must get over before growing seed of the chicories is to become comfortable distinguishing the chicories (C. intybus) from the closely related endive or escarole types (C. endivia). As these two species will only rarely cross, the important reason to be able to recognize their differences is so you will know when the recommended isolation distances are necessary and when they are not. Both have very similar blue-petaled, typical Asteraceae flowers that are hard to tell apart from one another unless you are quite familiar with the Cichorium genus. Even when you become quite familiar with the genus, the easiest way to distinguish between these two species is to look at the phenotypic differences between plant types of an endive/escarole and the various types of chicory, since there really are no chicories with the more lettuce-like leaves of endive or escarole. All seed growers who endeavor to grow either of these species need to be comfortable detecting these distinctions, as it can mean the difference between growing a pure chicory seed crop or one that could have considerable outcrosses in it. In other words, make sure that you definitively identify the species of any Cichorium crop growing anywhere in the vicinity of your seed crop. Because C. intybus and C. endivia are not usually sexually compatible, there is little concern with growing seed of these two species in close proximity. In experiments conducted in the Sacramento Valley of California in the 1950s, Charlie Rick found that crosses between these two species could occur at a very low rate but that it is difficult to produce a cross even when one is desired. Therefore, if there are in fact two crops, but they are from these different species, then using the basic isolation distances given for the self-pollinated endive/escarole crops should suffice to minimize the chance for any crossing between these two crop species (see Endive & Escarole, “Isolation Distances”).
If you are growing seed of one of the chicories (C. intybus) in a region where there are other chicory seed crops, then it is important to follow the general rule for isolating cross-pollinated crops that are primarily insect-pollinated. For commercial seed crops, if you have two chicories of the same crop type, the same form, the same maturity class, and the same color, then they need only be isolated by 1 mi (1.6 km) if grown in open terrain, or 0.5 mi (0.8 km) if there are substantial physical barriers between the crops (see chapter 13, Isolation Distances for Maintaining Varietal Integrity). An example of this among the chicories would be two red, round-headed, Chioggia-style radicchio varieties. However, even if you were growing two red radicchio varieties, but one was a more pointed, taller Treviso type and the other a Chioggia type, then the isolation would need to be increased, just as it would if you were growing two entirely different chicory varieties, as described below.
The isolation distance definitely needs to be increased to 2 mi (3.2 km) in open terrain if the second chicory seed crop is an entirely different crop type—for example, a radicchio and a witloof chicory type—or even if it is two different red, round-headed Chioggia types that are in two different maturity classes. This increased isolation requirement between two crops of the same species, but different types, can be reduced to 1 mi (1.6 km) if there are substantial physical barriers between the two crops.
Endive & Escarole
Endive is the catchall name frequently used in English for the loose-headed leafy salad crops in the species Cichorium endivia L. This includes the various crop types listed as endive, escarole, or frisée in many seed catalogs. All of these crops have distinctly ruffled to curled, pale green to yellow leaves with serrated edges. In the vegetative stage the outer leaves of the basal rosette are tougher and usually bitter, while the inner leaves often fold into one another as the plant matures and have a milder flavor and a lighter green, yellow, or cream color due to the partial blanching of this “heart.” Escarole varieties have broader, somewhat flatter leaves than the true endive type and are sometimes confused with green leaf lettuce by both the vegetable buying public and grocers. Endive has narrower, more curled leaves and includes the super-curled frisée varieties that are often used in salad mixes. Endive types are sometimes referred to as curly endive; escarole is also known as Batavian endive or simply Batavian in order to distinguish between these two types in the marketplace. It is important to understand that the degree of leaf curl is essentially all that distinguishes these two crop types from each other, and that they are fully sexually compatible.
‘Eros’ escarole (Cichorium endivia).
Endive’s ancestral origin is possibly from an area spanning the eastern Mediterranean basin and extending into the Middle East and southwestern Asia. There are several wild Cichorium species that shared this area with both C. endivia and C. intybus during the period of their domestication, and there are ongoing molecular taxonomic studies to try to clarify the relationships between them and their wild relatives. Unlike chicory (C. intybus), which has a weedy form that has followed humans to many temperate climates across the globe, endive is almost always only found as a cultivated crop (though occasionally feral populations are found in Italy). There has long been a theory that endive may have originated from a cross between chicory, which is undoubtedly the older cultivated form, and one of the wild Cichorium species. Endive’s origins as a crop may trace back to ancient Egypt. It was probably used as both a medicinal and a food plant in ancient Greece and in the Roman Empire. Endive spread to Northern Europe and was well established when it was described in the 16th century in England. Endive has long been used as both a cooked vegetable and a salad item. Its use is widespread across Europe and southwestern Asia.
The recent growth in endive consumption in North America, Australia, and South Africa is in part due to the boom of prepared salads. The fact that endive is so well suited to fall and winter production in the open in mild-winter areas of temperate climate zones bodes well for it given the growth of interest in year-round local food production and regionally supported markets.
Most of the world’s endive seed production is done in Europe, with a majority of it coming from the Netherlands, northern France, and a number of districts in Italy. It is a cool-season, dry-seeded species that needs more heat for ample seed production than what may be ideal for production of the market vegetable forms of the crop.
Crop Characteristics
Endive (C. endivia) has an annual life cycle, and it is highly self-pollinating in its reproductive habit. These two traits distinguish it from chicory (C. intybus), which is a biennial and is highly cross-pollinated. Endive flowers by elongation of the main stem and produces coarse, thick branches. Clusters of four to six sessile inflorescences are formed at the base of each branch, at each node, and at the end of each branch. Each inflorescence is made up of 15 to 25 single perfect flowers that are borne in an involucre of overlapping bracts, which functions much like the calyx of a simple flower. Each flower has five fused stamens that form a column enclosing the pistil. At maturity the stigma grows up through this column, coming in contact with the anthers and becoming covered with pollen. The ray florets form a ligulate corolla of pale to grayish blue (infrequently mauve) color that remains relatively closed through the time of receptivity. Endive is fully self-compatible, with a very high proportion of selfed seed, even in the presence of other C. endivia or C. intybus plants and insect pollinators. The combination of this self-compatibility and the semi-closed inflorescences results in very low rates of natural cross-pollination, probably far below 1% in most situations. However, cross-pollination can occur at higher rates in the right environmental conditions or the presence of certain species of pollinators, and adequate precautions should always be taken when growing a seed crop.
Climatic and
Geographic Suitability
The crops of the Cichorium genus are quite cold-hardy, easily overwintering in most parts of their centers of origin (the Mediterranean basin and Southwest Asia). Genetic variability for tolerance to cold exists between crop types and specific varieties, but endive will usually come through winter temperatures between 20 and 25°F (–7 and –4°C) with little damage, and selected endive populations are able to survive winter lows of 17°F (–8°C). Endive is best suited to temperatures between 58 and 68°F (14 and 20°C) for optimal vegetative growth. During the reproductive phases of flowering and seed growth endive flourishes at higher temperatures, but they shouldn’t regularly exceed 86°F (30°C) for high-quality seed. Cool springs that encourage good vegetative growth followed by seasonally dry summer conditions are desirable in order to obtain adequate yields and to harvest clean, disease-free seed. The growing season should be somewhat longer than that needed for many of the cool-season brassica and chenopod seed crops. Much of the commercial seed crop is produced in the Netherlands, northern France, and northern Italy. In North America the Willamette Valley of Oregon and a number of interior valleys of Northern California have proven to be well suited to producing high yields of high-quality endive seed.
Many seed growers have good success planting endive in the fall in order to establish a healthy plant that can take full advantage of all favorable spring weather, even during unsettled weather that makes it difficult to spring-plant. This ensures that the plants will have an adequate frame to produce a good seed set. Much of the commercial endive seed crop is planted in the early spring and must be given plenty of time to achieve a frame before the daylength and relative maturity of the plant promotes flowering.
Most endive varieties are fully annual and appear not to need a vernalization or cold treatment to initiate flowering. A number of authors claim that there are biennial endives. If a grower plants an endive variety in spring and it has little or no bolting, or if it has erratic bolting throughout the population, then it may be biennial, and it should be planted in the fall as described above. This should supply enough cold treatment in most temperate climates to fully promote flowering in any variety exhibiting biennial tendencies.
Seed Production Practices
Soil and Fertility Requirements
Endive seed production is suited to a range of soils that are well drained, yet have good water-holding capacity and moderate fertility. Soils with high levels of nitrogen will cause excessive vegetative growth and poor root development.
Growing the Seed Crop
Endive is more tolerant of hot temperatures than chicory or lettuce, but for seed production it prefers moderate temperatures that don’t regularly exceed 86°F (30°C), especially during flowering and early, rapid endosperm development. In climates where temperatures regularly rise above this after the summer solstice, it is best to fall-plant the crop so that the majority of flowering will be completed by late spring the following year, before the heat of the summer.
Endive can be transplanted, with the advantages including an early organic weed control (cultivation) of the field and the opportunity to plant older plants at an early date to maximize mature yield. You can also perform an initial selection for type in the greenhouse. However, many growers believe that by direct-seeding Cichorium crops into the field, the resulting plants will have more fully developed root systems, which will ultimately result in healthier plants with higher seed yields.
Cichorium crops can be treated much like lettuce for seed production, though they are decidedly more robust and often taller in stature than lettuce when flowering. Endive can be planted at a spacing of 24 to 32 in (61 to 81 cm) between rows, with a final within-row spacing of 14 to 20 in (36 to 51 cm). Drilling the seed at six to eight seeds per foot (30 cm) and blocking with a sharp precision hoe to the width of the desired spacing will help ensure an adequate stand and allow you to select the most vigorous, healthy seedlings in the field. A second pass across the field on foot will be required several days later to eliminate any late-emerging seedlings and check for any doubles—two plants at or near the same spot; these won’t produce satisfactory plants.
Weed control using standard mechanical cultivation practices can be employed, being careful not to injure the root system. Cichorium crops should not be hilled during cultivation. In arid seed production areas irrigation is indispensable. It is important to ensure the emergence of a uniform stand and to produce continuous, rapid growth, building a good plant frame for the reproductive phase of the life cycle, which in turn will produce good seed yields. However, overhead irrigation must be cut off from the seed crop once flowers emerge on the elongated flower stalk, as it can interfere with pollination and promote disease.
Seed Harvest
Proper timing of endive seed harvest is important to produce high-quality, mature seed without suffering any losses due to seed shattering. Seed of the Cichorium species is borne in fruits that are shaped like capsules or small barrels and can shatter relatively easily when fully ripe. As endive has an indeterminate flowering habit, it will often continue to set new flowers from onset of flowering until harvest. This means that you must make a decision on the time of harvest based on when the maximum quantity of fully mature seed is available, before an appreciable amount of mature seed has shattered. The most seed that you can hope to harvest from any one plant would be somewhere in the 60 to 80% range if you are growing the endive crop in a favorable climate. Having a uniformity of maturation between endive plants of a particular variety is common among endive varieties as they are largely self-pollinated and are thus often narrowly selected in the breeding process. This uniformity is important to ensure a crop of high-quality seed.
If seed is at an optimum maturity then you may not need to windrow plants (or can windrow for only a short time) before threshing. This is important to guard against shattering. Also, there exists some variation between different varieties and types in all Cichorium crops in terms of ease or reluctance in shattering, and this must be taken into consideration when harvesting their seed. For this reason plants are best cut for harvest early in the morning when the moisture from the morning dew decreases the rate of shattering. Conversely, threshing may be adequate to dislodge most of the seed from the capsules, but a percentage of these capsules that remain intact may require abrasion to break them apart. This can be accomplished through the use of a belt thresher.
Genetic Maintenance
Endive and escarole varieties are largely self-pollinated, and while they can cross with other members of C. endivia, these rare crosses can be largely avoided by following the isolation requirements specified below (see “Isolation Distances,” below). Crosses can also occur with the chicories (C. intybus), but at a rate of less than 1% according to an elegant experiment conducted by Charlie Rick at the University of California–Davis in the 1950s.
Variant forms in terms of leaf shape, color, and stature will occur naturally in endive and escarole, and these plants should be rogued out. The leaf shape, degree of curl, and form and distance between lobes should be monitored. Selection for intensity of color is important in named varieties, and some varieties will also have a distinct glossiness, which may vary. Selection is possible in an early rosette stage and is advisable at the market maturity stage. Tipburn is common in endive, and mass selection to eliminate the worst individuals with this malady has proven successful in lessening its severity over several generations. Selection should also be done to eliminate early bolters in almost all varieties.
As C. endivia is highly self-pollinated there are undoubtedly crossing events that occur in the presence of insects in the biologically diverse habitats found on many organic farms. The flowers remain closed until pollination and fertilization have been completed in almost all cases, although their form and color are much like those of the chicories, and they are visited by various species of bees and other pollinators. Precautions and recommendations given for lettuce are applicable for endive (see Lettuce, “Isolation Distances”). The minimum isolation distance between different crops of C. endivia should be 150 ft (46 m) in open terrain with no barriers but can be dropped to 50 ft (15 m) if there is a sufficient naturally occurring barrier between crops (see chapter 13, Isolation Distances for Maintaining Varietal Integrity, “Physical Barriers”).
Lettuce
Lettuce (Lactuca sativa) is the most important salad vegetable. Its succulent foliage is used as the base for salads in many cultures around the world. Lettuce consumption has steadily increased with the advent of refrigerated shipping after World War II, slowly replacing other lesser-known salad crops in affluent societies.
Lettuce is an annual crop with leaves borne as a basal rosette with a wide range of leaf types and colors. It is indigenous to the Mediterranean basin, where there is evidence that the Egyptians used lettuce more than 5,000 years bce. Several species of Lactuca exist in the wild, but L. sativa is not found outside of cultivation. Lettuce is probably derived from wild lettuce (L. serriola), a weedy species that grows in temperate zones around the world and that is fully interfertile with the cultivated crop. The ancestral form of lettuce was undoubtedly much like wild lettuce, with narrow spiny leaves, prominent midribs, bitter flavor, an abundance of latex sap, and a tendency toward early flowering (bolting).
Lettuce has six predominant morphological types:
1. Looseleaf types have a dense rosette of leaves that can be smooth, savoyed, or ruffled and are arranged in a loose configuration; they have little or no compact heart.
2. Crisphead types have a majority of leaves that form in a tight, overlapping fashion, resulting in a spherical, cabbage-like head with relatively few loose outer leaves. Crispheads are often erroneously called ‘Iceberg’ lettuce, which was an early successful variety of this type.
3. Butterheads also form a head, although it is less compact and smaller than the crisphead varieties. They also have broad, tender leaves that have a buttery texture and flavor and are easily bruised with handling and transporting.
4. Romaine or cos types have upright, oblong clusters of coarse, thick leaves with large midribs that overlap into loose head-like structures.
5. Celtuce types, also called stem lettuce or asparagus lettuce, are grown for their thick, erect stem, which is not unlike the bolting, flowering shoot of other lettuce types. This stem is peeled, and the succulent tender core is used as both a raw and cooked vegetable throughout China and in Egypt but is uncommon elsewhere.
6. Latin lettuce types have elongated leaves similar to butterhead types in their texture and may form loose, semi-closed heads. They are grown primarily in the Mediterranean region and to some extent in Argentina and Chile.
Seed production of this dry-seeded crop is best accomplished in a Mediterranean climate with a seasonal dry period for seed maturation and harvest preferred for high-quality seed. While the vegetable crop is thought of as a cool-season crop, lettuce requires warmer temperatures than many of the other cool-season, dry-seeded crops to fully realize its potential as a seed crop. For this reason lettuce seed is grown in the warmer reaches of climates where the seed of cool-season crops is traditionally grown, in places like the Mediterranean basin and the coastal valleys of the Pacific coast of North America. Conversely, excessively high temperatures during the reproductive stages of lettuce’s growth cycle may also cause lower seed yields and poorer seed quality.
Crop Characteristics
Reproductive Biology
Lettuce is a self-pollinating annual that produces a dense rosette of leaves early in the season, followed by flower stalk initiation, whereby the central cylindrical stem elongates, and indeterminate flowering may last for up 2 months. The flowers are borne in a fashion characteristic of most species of the Asteraceae (as described under the Asteraceae family, “Reproductive Biology”). In lettuce the 10 to 25 florets in each capitulum are all simultaneously receptive to pollination for only a few hours on the same morning, longer if the weather is cool and cloudy. Each floret produces an ovary that produces only a single seed if successful. If the weather is excessively hot, any capitula sexually maturing on that particular day may abort all their ovules. Fortunately, lettuce plants have indeterminate flowering and can continuously produce new racemes from the main stem of the plant for up to 2 months (or longer in some favorable climates). The structure of the lettuce flower promotes self-pollination, with the style pushing pollen out of the anthers as it emerges through the pollen tube. This usually results in a self-fertilization, but the pollen is then also available to pollinating insects, and cross-pollination can happen during their pollen gathering. Sticky and relatively heavy, the pollen is not windblown.
Climatic and
Geographic Suitability
Lettuces are grown across temperate climates worldwide. Moderate temperatures between 68°F (20°C) and 86°F (30°C) are best for production of both the vegetative and reproductive stages of lettuce. Many non-heading types have greater tolerance to temperature extremes outside of this range. Lettuce seed production is ideally suited to regions with a Mediterranean seasonal dry period during seed maturation and harvest, as rain can cause shattering of mature seedheads, sprouting of seed in the seedheads, and discoloration and diseases of the seed.
Higher temperatures and the longer daylengths of summer often accelerate flower initiation and bolting in many lettuce types. Celtuce and heirloom varieties are usually the first to bolt, therefore making it easy to mature a seed crop in most suitable temperate areas. Conversely, many modern crisphead, butterhead, and cos types have been bred to be daylength-neutral and are generally the most bolt-hardy lettuces, which can be problematic when trying to mature a seed crop in areas with shorter growing seasons.
Geographically, you must be sure that wild lettuce (Lactuca serriola) is not growing in your production area. This possible progenitor species of our cultivated crop has spread across the globe in temperate climates, and while it isn’t often found flowering in open, cultivated ground, it can be found growing in less disturbed ground near the fencerows and on the edges of fields, successfully reproducing. All lettuce seed growers should familiarize themselves with the characteristic leaf shape and the profile of the flowering plant of wild lettuce so they can increase their chances of spotting this rather unassuming weed and eradicate it within a minimum of 500 ft (152 m) from any production field.
Seed Production Practices
A closed, developing lettuce seedhead (top) and an open, fully mature seedhead (below).
Soil and Fertility Requirements
Lettuce can be grown on a wide range of soils for seed production, but soils must be well drained to minimize the chances of a number of lettuce diseases becoming a problem. Lettuce does well on lighter sandy or silt loams as a vegetable crop. It has rather shallow lateral feeder roots and requires a steady supply of water and nutrients throughout the season. When growing lettuce as a seed crop, many growers prefer somewhat heavier soils, like a clay loam or silt-clay loam that can more easily deliver nutrients and water to the crop over the course of the much longer season that is required to produce seed. These soils can be especially important for their ability to hold water during hot weather in late summer as the lettuce seed crop is maturing.
Adequate soil fertility that is sufficient to produce vigorous spring growth, to establish a good frame or basal rosette of leaves and support a bountiful seed crop, is mandatory. Soils that are rich in available phosphorus are desirable as P is essential for early plant development. This is especially important in areas with cool springs, as the mineralization of P in soils managed organically is low in cool weather. Nitrogen levels should be moderate; excessive foliar growth can be detrimental to producing a stout and sturdy flowering plant with a satisfactory seed yield.
Lettuce requires a long growing season to mature a seed crop. For this reason it is imperative to get the crop in the field and growing vigorously as early as your local climate will allow. The lettuce seed crop can either be direct-seeded into the field or planted from transplants. Producing the crop from transplanting has several advantages: First, the crop can be given 3 to 4 weeks of time to develop in the greenhouse or cold frame, when field temperatures are still too cool for active growth of the young plant. When the transplants are well past the seedling stage and able to put on rapid growth they are put into the field—as long as the spring weather has warmed and conditions are advantageous to their growth. Second, young lettuce plants with a minimum of four to six true leaves have several characteristics that are very representative of the mature plant, and this gives you an opportunity to make an initial selection to type. The color and any colored spotting that may exist in the variety is usually clearly evident in the seedling tray at this point; any off-types for these traits that may exist in a particular seed lot for a specific variety can be identified in the greenhouse and discarded before the variety is transplanted. The third advantage of transplanting the crop is cultural, as you can avoid the blocking and thinning as well as early weeding of the direct-seeded crop when the lettuce seedlings are young and have to compete with the first flush of weeds. Transplanting eliminates much of this intense hand work, which is often done on hands and knees; for that reason alone transplanting has become a standard practice for lettuce, endive, and chicory crops (and other crops with very small seedlings) for many organic farmers. It should be noted, though, that direct seeding of these crops does have its advocates. Some farmers will argue passionately that direct-seeded crops always outperform transplants as they will establish better root systems, both primary and secondary roots, by growing through their entire life cycle without being disrupted.
Spacing: Whether you’re direct seeding or transplanting, the final spacing of lettuce plants for seed production should be 12 to 16 in (30 to 41 cm) within the row and 18 to 30 in (46 to 76 cm) between rows. It is important for anyone growing lettuce seed organically to follow these guidelines and not be tempted to plant any closer, as the airflow through the standing crop is important to discourage the spread of foliar diseases. Cultivation should be shallow near the plants, as the lateral feeder roots lie close to the soil’s surface and are easily disturbed.
Irrigation: Lettuce requires a steady, relatively large quantity of water to produce optimum seed yields, because its root system isn’t very extensive. In conventional systems in the recent past this has often been accomplished through the use of overhead sprinklers during the vegetative stages of growth and then switching to furrow irrigation during flowering and seed maturation. Many organic growers are now using drip irrigation systems to good effect, but some still rely on overhead irrigation during the early stages of growth to establish a large, vigorous frame on their plants and ensure good yields, before switching to drip for the reproductive stage of the crop’s growth.
Maturing the Seed Crop: There is considerable variation in the amount of time that it takes for lettuce to bolt, and in many regions a significant number of varieties will not fully mature a seed crop before the season ends. It is wise for anyone new to growing lettuce seed to plant a number of prospective lettuce varieties as early as possible in the season to determine which will bolt and mature an appreciable seed crop in their climate. The longest-standing or slowest-bolting varieties are the crisphead types. They are the slowest to develop their characteristic heads of folded leaves and almost always are the slowest to bolt. Indeed, many crisphead varieties cannot be grown for seed in many of the shorter-season areas that can grow seed of other varieties. The next longest-standing types are many of the larger modern cos or romaine types, though some of the smaller varieties in this class can bolt much faster. The third longest-standing lettuce type is the newer, more highly bred butterhead from Europe, as older butterheads are usually faster to bolt. The looseleaf types are generally faster bolting than the first three, but there has been a lot more breeding of these types since the 1980s and many newer varieties are much slower to bolt than the older looseleaf varieties. The consistently fastest-bolting lettuces are the celtuce varieties. As the elongated stem of celtuce is the culinary item of interest, flower stem initiation has been selected for by the farmers who cultivated this crop for many centuries, causing it to occur early in the life cycle of the plant. Farmers growing a lettuce seed crop must determine which type of lettuce and which varieties within that type are suitable for seed production in their region.
Emergence of the Seed Stalk: In crisphead lettuces the seed stalk may not easily emerge, as the folded leaves forming the head are too firm and tight. This can result in delayed and distorted seed stalk development or elongated and possibly damaged flower shoots. Much modern conventional crisphead seed production involves applying synthetic growth regulators like gibberellic acid to the plant before it forms a head to promote early flowering. This is not an option for organic farmers and it is undesirable, as it doesn’t allow you to evaluate the crop for its trueness-to-type as a particular crisphead variety. To assist the emerging seed stalk three tried-and-true methods do not involve applying growth regulators:
1. Lancing the head with a sharp knife in a broad X cut on top, sometimes called racing.
2. De-heading, which involves stripping away outer leaves of the head to the point where the seed stalk can easily push through the innermost leaves of the heart and emerge.
3. Giving the top of the head a sharp blow with the palm of your hand and thus cracking a number of the crisp folded leaves to the point that they will easily break away as the seed stalk attempts to push out into the open.
Each of these methods requires practice and is best learned from someone with experience. De-heading is time consuming and normally only practiced in breeding nurseries with relatively few plants.
As individual lettuce seedheads mature, the calyx of the flower expands and dries, forming a parachute-like structure called a pappus that aids in wind dispersal of the seed—much like lettuce’s relatives the dandelions (Taraxacum spp.). The full expansion of the pappus is called feathering and signals the maturation of the seedhead. Lettuce has an indeterminate flowering habit, and as with other crops that mature seed sequentially, there is always the risk that the earliest-setting seed will mature and shatter before later-setting seed fully matures. In lettuce grown as a seed crop in a favorable climate, the earliest-setting seed often has a higher germination rate, presumably because it develops before the hotter weather of late summer, which does not favor the formation of large, well-developed embryos. Therefore, both of the seed harvesting methods described here emphasize a timely harvest to get the first flush of seed.
A mature and feathered lettuce seedhead.
Multiple Harvest: Hand-harvesting lettuce seed is still widely practiced and lauded for its ability to produce the highest-quality seed. The reason for this is that only seed that is fully mature is easily shaken from the plants; therefore no seed that has not fully formed will easily dislodge from the plant using this method. While hand-harvesting varies from region to region based on climate and preferred practices, the basic steps are as follows. When between 35 and 50% of the seedheads have feathered, harvest crews with cloth sacks go through the field shaking the flowering portions of each plant vigorously into the sack, being careful not to damage the plants. This is then repeated in 7 to 14 days, depending on how fast the seed is maturing and showing another flush of feathered seedheads. In some climates a third or fourth harvest may be possible, but you should evaluate later-
setting seed for its quality on a number of occasions in order to make this judgment and not waste time harvesting poor-quality seed.
The multiple-harvest method, as practiced on the small scale, has its pros and cons.
The presumed advantages of this method are: (1) You are only harvesting fully mature seed in stages—seed that is ready to shatter, or dislodge from the plant into your harvest sack; and (2) you lose less seed to early shattering or birds than you would with a more mechanized harvest approach, where growers often wait for a higher percentage of flowers to feather before harvesting in order to maximize yields. Unfortunately there are several disadvantages to consider with the multiple harvest method. First of all it requires more labor than other mechanized methods, with many hours of bending and shaking required over repeated harvests. Second, it is a dusty, dirty job. With each shake comes a cloud of dust from the surface of the plant as well as pieces of the pappus that are propelled into the air. Workers should always wear face masks during this process.
Single Harvest: The perception that machine-harvested lettuce seed is inferior is based primarily on the fact that it usually occurs when growers harvest seed using the single-harvest system often used by larger producers. When seed is harvested at any one moment in the long flowering period, many immature seedheads are threshed with the fully mature seed when the entire plant is threshed. With many other indeterminate flowering crops the less mature, poorly developed seed is easily eliminated during cleaning, as they are usually smaller and considerably lighter in weight than mature seed and can thus be removed by winnowing or screening. With lettuce this is not as easily done, as much of the undeveloped seed is not any smaller and is not appreciably lighter than normal seed and is not readily removed using these methods.
The basic method for harvesting lettuce seed currently used by most large-scale seed producers involves hand crews cutting the plants near their base when about 50% of the flowers on most of the plants in the field have feathered. Then they lay the plants into windrows and mechanically thresh the seed when the plants have dried sufficiently, before excessive shattering occurs. This method will often result in as much as a 10% drop in germination percentage, due largely to the immature seed content.
Frank Morton and his crew at Gathering Together Farm in Philomath, Oregon, have developed an improvement of this harvest method in their organic seed operation. Instead of cutting the lettuce plants off at the time of harvest, they pull the entire plant by the roots and then lay most of the plant onto a 6 ft (1.8 m) wide strip of landscaping fabric that has been unrolled along the edge of the patch. They are careful to not get the root-ball or any soil onto this fabric, as its main purpose is to catch shattering seed that may fall while the plants are laid down in a windrow or as the seed shatters over the next 7 to 10 days. The reason that the root-ball is kept intact is so the plant is kept barely alive for the first few days of this process, delivering all possible energy to mature the seed that is only partially mature. The plants are stacked three or four deep on the fabric from both sides with the tops of the plants just barely touching in the middle. This creates a mound of plants that is about 3 ft (0.9 m) high while the plants remain green with a mound of root-balls on each side about 1.5 ft (0.5 m) high. This mound of plants will keep most of the seed inaccessible from any birds that may show up to eat the seed off plants while they dry. The American goldfinch (Carduelis tristis) that is native to much of the North American continent is notorious for this and will get many of the seedheads near the top of the pile, but a finch will not venture down into the mounds if they are piled properly.
The use of a heavy grade of landscape cloth can be very important if there is rain while the crop is drying in the windrow. If there is only a short period of rainfall that delivers measurable precipitation but passes quickly, then the rain reaching the fabric will easily pass through it and the crop and any seed on the fabric will then be able to dry quickly. In several instances when a longer period of wet weather has threatened, Frank has taken a chain saw and cut the root-balls off the drying plants, then carefully rolled each strip of landscape fabric with the plants into a large roll that looks like a jelly roll. These rolls, which Frank calls “Morton’s Jelly Rolls,” can then be covered with tarps in the field; if wet weather persists for a longer period of time, they can be lifted onto a trailer or truck bed and be moved to shelter. They then can be held temporarily as a jelly roll and returned to the field as the weather clears or be unrolled and dried under cover. If kept under shelter you should ensure good airflow and possibly heat if cool, wet weather persists.
At the point when the crop in the windrows is almost completely dry, it is important to turn it to ensure even drying. This needs to be done gently to minimize shattering. To ensure that all of the seed is as mature as it can be when preparing to thresh, dry the crop to the point where the plant is thoroughly dry and leaves are crisp. However, the crop should be threshed in the mid- to late morning when plants are still pliable from the morning dew, but late enough in the morning so that the free moisture from the dew has dried. The pliability will help keep the small stems attached to the seedheads from breaking into many small pieces.
Threshing Lettuce Seed: Threshing lettuce manually can be done with a flail, pole, or rake. The ripened seedheads will shatter easily when the plants are sufficiently dry. Mature lettuce plants that are standing and are thoroughly dry, or plants that are dried in windrows, can also be threshed mechanically. However, care must be taken when using threshing equipment; adjust the intake reel so that the relatively fragile lettuce seed receives minimum impact in the threshing process. It is a widely accepted fact that lettuce seed that is mechanically threshed can have germination percentages that are as much as 10% lower than lettuce seed harvested manually.
Many seed people claim that the rotary bar on threshers can also damage lettuce seed, dropping the rate of germination unless you’re skilled at properly adjusting the equipment for lettuce.
Genetic Maintenance
Maintaining the genetic integrity of lettuce is best accomplished at several different stages of its life cycle. As many people now start the lettuce seed crop in the greenhouse, it is possible to easily select for several obvious traits while the lettuce is in the seedling stage. Once the lettuce plant establishes its first four to six true leaves it is quite easy to distinguish whether the color of individual plants matches the varietal norm and whether any spotting, streaking, or other color demarcations that are present are consistent for that variety. All seed growers should also always be mindful of selecting for vigor in their genetic stocks at the seedling stage, as it has repeatedly proven to improve seedling vigor for a number of crops when practiced over several cycles of selection.
Red and green lettuce varieties in the field.
When the lettuce plants are at or near the transplanting stage (8 to 12 true leaves) it is possible to judge and select for the stature of the plant, whether it is upright or prostrate to the ground. It is also possible to distinguish whether a leaf is entire or lobed, if it is smooth (flat) or savoyed, if it is blistered or not, and to select for the overall shape of the leaves. As the plants approach their optimum size for harvest as a vegetable it becomes possible to select for the thickness and the glossiness of the leaves, as well as the degree of tightness of the head (for example, butterheads have smaller, looser heads than crisphead varieties)—or the absence of heading. It is also a good time to do a final selection for color, spotting/streaking, leaf shape or type, and stature before the plant bolts.
Selection for time of bolting is always important in seed crops. In lettuce there should always be selection pressure against early bolting, as the early bolters are very undesirable for anyone growing lettuce as a vegetable crop. However, as stated in the “Growing the Seed Crop” section, some lettuce varieties require such a long season to reproduce that they won’t successfully make seed in some regions. Therefore, if you’re selecting against early bolting you must be careful to not shift bolting too far in the opposite direction in some genetic backgrounds.
During the reproductive phase of the life cycle many organic seed growers will lose a significant percentage of their lettuce seed crop to Sclerotinia sclerotiorium. This fungal pathogen is rarely a problem during the vegetative phase of the plant’s life cycle but can be particularly troublesome during the reproductive phase. It is characterized by a cottony growth that can often first be seen in older leaves after the floral shoot has emerged and will then often emanate from splits or cracks in the lower section of the flower stalk. Infected plants should be removed as soon as they appear to eliminate susceptible plants from the population. Frank Morton of Wild Garden Seeds has selected against this disease for a number of years in his lettuce breeding work, and it has resulted in marked increases in horizontal resistance to the effects of this fungal pathogen in a number of his selected varieties.
From left, the author, Frank Morton, and Micaela Colley identifying lettuce plants with resistance to downy mildew in Frank’s disease nursery, affectionately known as Hell’s Half Acre, Philomath, Oregon.
As L. sativa is highly self-pollinated there are undoubtedly crossing events that occur in the presence of insects in biologically diverse habitats found on many organic farms. The flowers remain closed until pollination and fertilization have been completed in almost all cases, although their form and color are much like those of the other members of the Asteraceae family and are visited by various species of bees and other insect pollinators. The minimum isolation distance between different crops of L. sativa should be 150 ft (46 m) in open terrain with no barriers, but can be reduced to 50 ft (15 m) if there is a sufficient naturally occurring barrier between crops (see chapter 13, Isolation Distances for Maintaining Varietal Integrity, “Physical Barriers”).