The Fabaceae is a very diverse, large family of plants that includes more than 450 genera and over 12,000 species of annuals, biennials, and perennials. The members of this family have traditionally been called legumes. Botanically the term legume denotes a simple dry fruit in the form of a pod that develops from a single carpel and usually dehisces, or splits, at maturity into two halves (called valves), with the seed attached to the edge of one of the valves. The French refer to all garden vegetables as legumes. Well over 100 leguminous species are cultivated as agricultural crops worldwide, which includes forages, pasture crops, cover crops, pulses, vegetables, and ornamentals. Most of the 40 species used in the human diet are annual pulses, which are legumes harvested primarily for their protein-rich dry seed. Indeed, the pulses of the Fabaceae are second only to the cereal grains in their importance as a source of human nutrition worldwide.
The Fabaceae includes several crops used as vegetables. The first class of vegetable legumes includes several crop types where the well-developed immature seed is shelled from the pod and lightly cooked. Examples are horticultural beans, runner beans, garden peas, limas, favas, cowpeas, and edamame soybeans. Another class of vegetable legumes is grown for their succulent, immature, edible pods and underdeveloped seed and includes snap beans, snow peas, yardlong beans, and, to a lesser extent, runner beans and some types of cowpeas. Some version of this diverse group of vegetable legumes, usually more than one, is grown in most cultures around the globe.
Vegetable legumes and sweet corn are collectively called the large-seeded vegetables in the North American seed trade. Due to their large size, planting these crops requires a large amount of seed on a per acre/hectare basis. In North America, Europe, and Japan most of the commercial seed crop of these vegetables is grown in areas with low humidity; clear, warm, sunny days; and cool nights to help ensure disease-free seed. However, in many other parts of the world this is too expensive a proposition for the relatively large amounts of seed required; therefore much of the seed of these crops is still produced regionally.
Family Characteristics
Legume flowers have blossoms with an irregular shape that is fancifully described as resembling a butterfly. The typical legume flower is perfect, with five petals consisting of one large, oval banner or standard, two elongate keel petals that are fused together enclosing 10 stamens, and two wing petals. Nine stamen filaments are united into a sheath that surrounds the pistil; one is separate. The petals of the vegetable legumes are often white but may also be many beautiful shades of pastels, ranging from deep violet, purple, pink, and salmon to shades of red. The most commonly grown runner bean, ‘Scarlet Runner’, is often grown as an ornamental because it has striking scarlet flowers.
Legume ovules are borne in a simple carpel with a leathery pericarp (the wall of the fruit or pod) that becomes dry at maturity and usually dehisces (splits) along two sutures of the valves to release the seed. In some legume seed crops this dehiscence may happen with very little physical prompting; in fact, even a stiff wind rustling through unharvested mature dry pods can cause the pods to pop as they shatter and release their seed to the ground. Among the vegetable legumes this can especially be a problem with many edamame varieties.
Most of the species that make up the Fabaceae vegetables (see the Runner Bean section for a notable exception) are usually self-pollinated, as the anther sacs are borne directly adjacent to the stigma and the pollen is released the day before the flower normally opens. Therefore, under most conditions this self-pollination leads to a full complement of selfed seed that is genetically true to type before the flowers are open and accessible to any insect activity. However, there are several situations that lead to outcrossing between legume plants of the same species. First, if you are growing these crops adjacent to areas with biologically diverse habitats for insects, there is sure to be a higher and more diverse number of insect pollinators that will forage in your fields. These pollinators may be able to get into legume flowers before they fully open, either because the flowers are not completely closed (a genetic trait) or because the insects may be able to pry the flowers open in search of nectar or pollen.
Another common reason for outcrossing involves a combination of excessively hot weather and the fact that, in many of these crop species, certain varieties have pollen that will abort (due to sensitivity to heat) more readily than other varieties of the same crop. So if several varieties of the same crop with genetic variation for this trait are grown in the same field, chances are some will be more sensitive to the heat (and not have viable pollen) than others. If insects are present and actively visiting flowers, then they are apt to move pollen from male fertile varieties to those affected by the heat (and not producing viable pollen) and create a large number of unwanted crosses. It should be noted that heat usually affects pollen viability unfavorably long before the comparable female cells, the ovules, are damaged. (See chapter 2, Reproductive Biology of Crop Plants.)
The threshold for crossing to occur will be at a hotter temperature for some of the vegetable legumes than for the others. For example, cowpeas, yardlong beans, and limas are all originally from tropical or subtropical climates and are able to reproduce successfully under considerably higher temperatures than the other vegetable legumes that are adapted to temperate conditions. Peas and fava beans represent the other end of the spectrum: Both favor cooler temperatures during flowering for ideal seed set.
Climatic Adaptation
There is a broad range in the adaptation to climate among the vegetable legumes. Some species, including favas and peas, can tolerate frost and are often planted 6 to 8 weeks before the last hard frost of the spring. The other vegetable legumes are tender, heat-loving crops; when grown as vegetables, they are usually planted when all chance of frost has passed. But when these species are grown as seed crops, they are often planted early to ensure full maturity before the end of the season. This is especially necessary in temperate climates, or in climates where late-summer or early-fall rains threaten the quality of the crops. This is possible in part because most of the vegetable legumes are more frost-hardy at emergence (although this seedling hardiness doesn’t last long) than they are as mature plants at the end of the season.
All of the vegetable legumes are grown as annuals in temperate climates with the exception of fava beans, which are often treated as winter annuals in areas with mild winters. As with all annual seed crops, it is very important to be familiar with the relative maturity of the crop species in the area that you are considering for production. Not only should you be assured that the particular crop type will faithfully mature in your climate, but you should have firsthand knowledge or experience with the specific variety of that crop that you are considering for production. It should be a reliable cropper that will mature satisfactorily in your bioregion, even when faced with a less-than-optimum growing season.
Seed Harvest
and Cleaning
Proper timing of harvest is important in production of high-quality legume seed that is fully mature, has a high germination percentage, and has maximum storage potential. Gauging the best time to cut, cure in a windrow, and thresh the crop is complicated by the fact that differences between crop species, as well as variety-to-variety differences, abound. The initial signal that the crop is ready to cut is the relative maturity of the pods and their color at or near the time when they are breaking, or when they first turn yellow, mahogany, or buckskin in color, depending on the crop species. The exact desired color is crop-specific and may also be variety-specific within each crop type. For many of the vegetable legumes it is best to cut the crop before the pods have dried to a papery crisp texture. Maturation to the papery stage may increase the danger of seed shattering during harvest. The seed crop should be cut when approximately 70 to 80% of the pods on the plant are of the desired color and texture.
Harvesting the seed of the vegetable legumes is a multistep process. The first step is to mechanically undercut the stems of the plants just below the soil surface, allowing the plants to wilt in place for a day. The next day the plants are raked into windrows. Depending on weather conditions, the windrows should cure in the field for at least 10 days to 2 weeks, with a possible turning of the rows near the halfway point. Threshing of beans is best accomplished during the heat of the day, when the pods are brittle and easily cracked. Seed should then be further cleaned to separate it from any plant debris that may be moist. If the seed is not sufficiently dry, it may require air- or kiln-drying before being stored for a final cleaning and conditioning.
Isolation Distances
While the vegetable legumes are all considered self-pollinated species, crossing will occur in all of them to varying degrees. Much of the seed-growing literature tends to treat these crops as if outcrossing is only a rare occurrence, and the only isolation that is recommended for different crop varieties of the same species is 10 to 15 ft (3–4.6 m).
For the vegetable legumes that are largely self-pollinated—common beans, garden peas, and the edamame class of soybeans—this distance may suffice, especially in conventional cropping systems that are largely planted to one species and have a minimum amount of biological diversity in the form of insect pollinators. Indeed, these crops usually have relatively low incidences of cross-pollination (less than 1%) in most commercial seed production areas of North America. However, the incidence of outcrossing is often higher in self-pollinated vegetable crops with the increase in biological diversity that usually accompanies organic cultural practices or when environmental stresses are present.
For this reason common bean, garden pea, and edamame require a greater isolation distance between varieties of the same species under organic production conditions than what is often stated in the literature. The isolation between different varieties of each of these crops for commercial seed production should be at least 150 ft (46 m) in open terrain. For stockseed or foundation seed this number should be doubled, and a tall barrier crop such as corn or sunflowers planted between crops if no other natural barrier like woods or farm buildings are present.
The other vegetable legumes—cowpeas, favas, limas, and runner beans—are all more promiscuous than the aforementioned crops, with crossing rates that sometimes exceed 5%, especially when grown in biologically diverse settings or under environmental challenges. For this reason special consideration is given for the isolation distances for each of these crops under their respective sections.
Common Bean
The wild ancestors of the modern common bean (Phaseolus vulgaris L.) come from Central and South America. These ancestral types are found across a range of environments, from hot, arid climates to humid, lowland tropics, and even into cooler, upland areas of South America. The beans of this species that are grown in North America today are grown in a more limited temperate climatic zone. Nearly all modern agricultural varieties have a determinate bush habit, whether they are dry bean, shell bean, or snap bean types. Older varietals, landraces, and heirlooms are often indeterminate and vining. The snap bean types are grown for a harvest of tender young pods with immature seed that are eaten as a fresh vegetable. While immature pods of any common bean variety were once commonly eaten, there are now literally thousands of varieties that have been selected to have fleshy pods with slow seed maturation for a crop that has become a vegetable mainstay in our culture. Snap beans are alternately called string beans, green beans, and garden beans. The term snap bean refers to the way in which fresh garden beans are broken or snapped by hand into short segments before cooking. Garden beans is what they are most often called in the bean-seed-growing regions of the Northwest to distinguish them from the more widespread dry beans or field beans of this same species.
Whether grown as a vegetable or for seed, beans are produced as an annual crop that matures in one growing season. Bean seed crops may require a long season to mature (on average 90 to 120 days) and must be planted early enough to mature and dry prior to fall frosts or rains. Commercial bean seed production is focused in the western region of the United States, as the long dry summers and arid climate create good growing conditions with lower disease pressure and a long season for maturation.
Crop Characteristics
Reproductive Biology
Nearly all modern agricultural varieties of common bean are daylength-neutral in their flowering response. In other words the length of day does not determine flower initiation, and plants flower as soon as they are physiologically ready. There are exceptions to this in some bean varieties from the tropics and some temperate dry bean varieties. Many tropically adapted common beans are short-day plants and fail to flower until the days shorten in late summer. Because there is varietal variability in flowering response, it is recommended that you grow a small plot of any new seed crop to see if it matures optimally in your particular region.
Common bean flower (Phaseolus vulgaris).
Common bean flowers have the shape and structure of a typical legume flower. Their petals are usually whitish but may be tinged deep violet, purple, or red. There are five petals consisting of one large, oval banner or standard, two elongate keel petals that are fused together enclosing the stamens, and two wings. Nine stamen filaments unite into a sheath that surrounds the pistil, with one stamen filament separate from the fused nine. Common beans are highly self-pollinated, as the anther sacs are borne directly adjacent to the stigma (the receptive part of the female flower) and the pollen is normally released the day before the flower opens. Under most conditions the flowers are self-pollinated before they open and become accessible to insect activity. However, there are some environmentally influenced situations that can cause an increased rate of cross-pollinations (see “Isolation Distances”).
Climatic and
Geographic Suitability
Common bean is a tender warm-season crop that requires warm, well-drained soils for germination. Temperatures of 70 to 80°F (21 to 27°C) are preferred for optimum crop growth. Temperatures below 50°F (10°C) or above 90°F (32°C) during flowering may adversely affect pod set and seed yields. Most snap bean cultivars germinate best when soil temperatures are at or above 65°F (18°C), but germination may be inhibited at temperatures above 95°F (35°C). There are instances when seed growers must plant with soil temperatures that are below optimum in order to fully mature a seed crop by the end of the season. Considerable differences exist between cultivars in their ability to germinate in cool, moist soils and to resist common root rot organisms that can damage or destroy seedlings. It is commonly believed that the French filet types and the modern white-seeded snap bean types are the most susceptible to these maladies.
Seed Production Practices
Soil and Fertility Requirements
Soil conditions and types may vary and still produce healthy plants and superior seed, but adequate drainage is essential, as beans are sensitive to both moisture stress and waterlogging. Early plantings for long-season varieties are best done on light sandy soils. Soils that easily crust should be avoided, and irrigation and tillage managed to avoid crusting; seedling emergence may otherwise be impaired. All crop residues should be thoroughly incorporated into the soil prior to planting. Residues on the surface can interfere with seed placement during drilling and result in inadequate coverage of weeds with soil during an early cultivation. Incorporation of residue is additionally crucial in the availability of nitrogen (and other nutrients) to the young bean plants before their development of symbiosis with the Rhizobium bacteria.
Common beans are frost-sensitive, so the usual recommendation is to plant after all danger of frost is past. However, it is often necessary to plant a seed crop 7 to 10 days before the last anticipated frost date, either to allow time for full maturity and harvest prior to inclement weather in the fall, or in some cases to avoid the heat of summer during flowering. Soil temperatures do need to be warm, approximately 65°F (18°C), so the seed will germinate quickly and not succumb to root rots in cool soils. However, young plants with fleshy cotyledons are more frost-tolerant than mature bean plants and can tolerate a light frost soon after emerging.
Bean seed should be planted at a depth of 1 to 1.5 in (2.5 to 4 cm) below the surface of the soil after the press wheel has packed the soil. Common beans for seed are routinely grown on 22 in (56 cm) row centers with an in-row density of six to eight bean plants every 12 in (30 cm). Seed may be inoculated with Rhizobium bacteria prior to planting to enhance nitrogen availability. This may be particularly beneficial when planting on soils where beans have not been produced in recent years. Prior to planting beans, soils are commonly pre-irrigated, allowed to dry to moderate soil moisture, planted, and then not irrigated again until seedling emergence. This avoids soil surface crusting prior to seedling emergence. Alternatively, soil crusting is mitigated by a very shallow dragging of soil with a harrow prior to emergence.
Weed control is particularly critical in organic bean seed production to achieve optimum growth and prevent weed seed contamination in harvested seed. One very successful method used for weed control under organic production is as follows: Plant single rows in hills that are 6 to 8 in (15 to 20 cm) high. After 4 to 5 days, when seed has sprouted but the epicotyl is still 1 in (2.5 cm) belowground, cultivate the hills for the first time using a drag harrow. The drag harrow will scrape off the top surface of each hill, exposing the first set of tiny weeds before they can become established in the bean rows. Even if done properly, an occasional bean plant will be lost, but it is well worth the effort to eliminate the first within-row weeds.
The next cultivation is done after the bean plant has emerged and has one set of true leaves. Set up two tool bars on a cultivating tractor. The first tool bar should have shanks with chisel points that are set as close to the bean rows as possible. These chisel points will disturb the soil (killing weeds) close to the plant as well as throwing some soil up onto the base of the plant to smother other weed seedlings. Follow these shanks with a second tool bar with “duck feet” sweeps, which will disturb the soil, kill weeds between the rows, and throw soil back onto the hills to rebuild them. Subsequent cultivations are done with knives that cut soil away from the bean plants, and sweeps between the rows to rebuild the hills. In addition to disturbing as much of the soil surface as possible to uproot or bury weed seedlings, it is important to create hills high enough to facilitate undercutting the bean plants at harvest. Cultivation should be done with attention to avoiding major root disturbances as the plants get larger.
Proper timing of harvest is important in order to produce high-quality bean seed that is fully mature, has a high germination percentage, and has maximum storage potential. Each variety has its own specific harvest timing, and while this makes overall recommendations for gauging cutting, curing, and threshing difficult, there are basic signs that indicate maturity. The initial signal that the crop is ready to cut is the relative maturity of the pods and their color at or near the time when they are breaking, or when they first turn yellow, mahogany, or buckskin in color but haven’t gone to the tan, papery shade. Maturation to the brown, papery stage increases the danger of seed shattering during harvest. Pods should generally be yellow at harvest in order to mature properly in the windrow, but the exact desired color may be variety-specific. The crop should be cut when approximately 70 to 80% of the pods on the crop are of the desired color and point of breaking. The stems of the crop are undercut mechanically just below the soil surface and left in place for a day. The next day the plants are raked into windrows. Depending on weather conditions, the windrows should cure in the field for at least 10 to 14 days, with a possible turning of the rows near the halfway point. Threshing of beans is best accomplished during the heat of the day when the pods are brittle and easily cracked. Seed should then be further cleaned to separate it from any plant debris that may be moist. If the seed is not sufficiently dry it may require air- or kiln-drying before being stored for a final cleaning and conditioning. Physical mixing of seed varieties can be a source of variety contamination. Attention should also be given to thoroughly cleaning out harvesting and cleaning equipment between harvests when you’re working with different varieties.
Genetic Maintenance
There are very few stages in snap bean growth in which genetic differences within a variety are apparent. If you are able to establish a uniform stand, then it is possible to perform selection for speed of seedling emergence, seedling health, and overall vigor—all essential traits for organic production. If you routinely rogue out late-emerging, low-vigor seedlings, you’ll see improvement over cycles of selection for these traits. Many bean growers can easily identify differences between pod characteristics, flower color, and the presence of runners, but other plant characteristics are only apparent to experienced farmers who specialize in the crop. For some traits, such as leaf shape, color, and plant stature, it is possible to evaluate the plant and rogue it to type before flowering has begun. Flower placement, timing, and duration of flowering can all be selected during flowering. Pod characteristics such as color, shape, and length are also notable to the experienced grower and can be selected. Additionally, it is critical to rogue for disease in bean crops in order to produce quality seed, minimize risk of seedborne diseases, and select or maintain for a cultivar’s disease resistance.
Common beans are considered to be highly self-pollinating by most commercial seed producers. In the seed production areas of southern Idaho the isolation distance between different varieties of common bean is usually no more than 10 to 15 ft (3 to 4.6 m), with a few rows of a taller crop such as corn planted in between to act as a barrier to deter pollinator movement. This minimal distance and physical barrier between common bean varieties is even used in stockseed production. And indeed, in the Treasure and Magic valleys of Idaho, this seems to be adequate isolation, as only a very low rate of crossing is ever detected in the seed lots produced there. This is probably due in large part to the almost ideal environmental conditions that exist in this region during the growing season for the reproductive ability of this crop (not excessively hot, cool nighttime temperatures, low relative humidity, and a low incidence of wild pollinators interested in this species).
However, there are several situations that can lead to outcrossing between bean plants, including these:
1. When beans are grown adjacent to areas with biologically diverse habitats for insects, there is usually a higher and more diverse number of insect pollinators present. These pollinators may be able to get into flowers before they fully open, either because the flowers are not completely closed (a genetic trait) or because the insects may be able to pry the flowers open in search of nectar or pollen.
2. Variety differences of floral structures exist, and some varieties (particularly pole beans) have longer pistils that extend farther out of the flower, making cross-pollination more likely.
3. An increase in rate of crossing can occur due to a combination of excessively hot weather and the fact that some bean varieties are more sensitive to heat than others. The pollen of many bean varieties can be damaged and become non-viable if temperatures are too high at the time of flowering, whereas the stigma will usually remain unaffected. There is genetic variation for this condition among bean varieties, so the pollen of one variety may lose viability while another does not under similar conditions. If multiple varieties are being produced during a hot period, it is possible that pollinating insects may move pollen from a fertile variety to another variety lacking fertile pollen and create unwanted crosses.
The common recommendation for isolation distance between common bean varieties is usually to allow “enough room to avoid mechanical mixing.” However, as with the other largely self-pollinating species of the Fabaceae, it is appropriate to observe the minimum 150 ft (46 m) isolation distance if you are growing more than one variety in open terrain with no natural barriers to ensure a high level of genetic purity. If producing multiple common bean crops in areas with natural barriers (see chapter 13, Isolation Distances for Maintaining Varietal Integrity), then the distance can be dropped to 50 ft (15 m) or so to minimize crossing.
It is often stated by experienced seed growers that the vining or pole varieties of common bean are more prone to outcrossing than bush varieties. Definitive information on this is not readily available, although the strict standards stated above for common beans in general should minimize the extent of crossing in all forms of this crop species.
Edamame
Edamame is a type of soybean (Glycine max [L.] Merr.) that is harvested at an immature stage and used as a vegetable. This crop, which is sometimes known as green vegetable soybean in English, is called mao duo in China and poot kong in Korea but is best known internationally by its Japanese name edamame. The pods of these vegetable types are harvested when the seed has attained 80 to 90% of its full size within the pod. Edamame seed is larger and usually has a greener color than the more common oilseed soybean, both at this stage and when mature. Historically, the soybean is one of the oldest crops known to Chinese agriculture, predating written records. The vegetable types of soy are presumed to be a later-derived crop from the staple soybean. The earliest recorded use of mao dou in China dates to 200 bce; the earliest Japanese reference to “aomame” is in a guide to agricultural commodities in 927 ce. Edamame was first introduced in the United States in 1902 by the famous plant explorer of the USDA, David Fairchild, who brought seed back from Japan. However, the real interest in this crop outside of Asia came only with an explosion of interest in international foods at the turn of the 21st century.
Crop Characteristics
Reproductive Biology
Edamame soybeans have flowers that in form and structure are typical of the pulse crops of the Fabaceae, though they are smaller and less conspicuous than the flowers of the other vegetable crops in this family. Flower color varies from white to lilac and other shades of purple. Soy flowers are highly self-fertile and are not regularly visited by insect pollinators in most situations. The anthers dehisce and shed pollen before the flower opens, with pollination and fertilization occurring before insects have access to flower parts. However, crosses between varieties do occur when large numbers of pollinators are present.
The flowering habit of most edamame varieties is strongly indeterminate, as this type of soybean has been selected for extended harvest as a vegetable crop. The pods are produced in clusters. Each pod usually contains from two to three seeds. Pods that retain a green pod color as the seed matures are desirable for the fresh market; many modern varieties retain their green color through to full maturity. Edamame seed is often globe-shaped and may be slightly flattened at maturity.
Climatic and
Geographic Requirements
Optimum growing conditions for edamame seed production include mean temperatures between 68 and 86°F (20 to 30°C) and seasonal dry conditions during seed maturation and harvest. Temperatures below 68°F (20°C) will slow vegetative growth and the development of flowers and subsequent seed. As with most heat-loving crops, temperatures between 50 and 54°F (10 to 12°C) and below may inhibit pollen development, fertilization, and seed set.
While many soybean types are short-day plants, most edamame varieties are daylength-neutral and can be produced across a wide range of latitudes. It is often hard to find information on whether a particular edamame variety is daylength-sensitive. Ultimately, the best way to determine if there is a problem for your latitude is to grow a small amount of a given variety, making sure it flowers in a timely fashion and matures a seed crop during the normal harvest period for your climate.
Seed Production Practices
Soil and Fertility Requirements
Soil conditions and fertility requirements are the same as those recommended for garden peas (see Garden Pea, “Soil and Fertility Requirements”). If you are growing soybeans in a particular field for the first time, then inoculating the seed with Rhizobium japonicum before planting is recommended.
Growing the Seed Crop
Edamame-type soybeans are a frost-sensitive crop that have a bush stature and form a canopy much like most bush bean varieties; therefore, it is recommended that you plant and cultivate the crop per the recommendations for bush-type common beans (see Common Bean, “Growing the Seed Crop”). Similarly, for many growers in temperate regions, the ability to mature a seed crop of this indeterminate-flowering type of soybean in a timely fashion (before fall rains and possible frost) may require planting the crop 7 to 10 days before the last anticipated frost date for your region. This type of early planting should only be attempted when the weather is warm and clear during the day and soil temperatures are at or approaching 65°F (18°C), which helps ensure that the seed germinates quickly and will not succumb to root rot organisms in cool soils.
Seed Harvest
As with all Fabaceae crops, proper timing of harvest is important in producing high-quality seed. In fact, the timing of the edamame seed harvest may be more sensitive than other vegetable legume seed crops. Edamame varieties have been selected for easy pod separation, as the fresh crop is traditionally eaten from the cooked green pod by squeezing open the pod and popping the beans into your mouth. This characteristic also influences the behavior of the pod on the growing plant. As edamame pods approach full seed maturity and become dry and brittle, they can easily split apart along the suture that separates the pod halves. This seems to happen almost spontaneously, and farmers standing in the field on a hot, dry day are always amazed at the audible popping sound of pods shattering around them when they hear it for the first time. Whether it is the breeze or some other slight movement that provokes this response, it is a flaw that can cause appreciable amounts of seed to shatter in the field before harvest unless you monitor the crop carefully.
In order to harvest edamame seed successfully you must watch closely for the first plants that will invariably mature their pods before other plants in the population. The pods will have the unmistakable leathery, tough-skin look as they turn to a tannish brown color that many growers in the western United States refer to as buckskin. The transition of a few plants to a majority of plants expressing this change is quick and dependent on the weather. Under warm, sunny conditions the crop will need to be cut when a majority of the pods (70 to 80%) have this buckskin appearance but haven’t yet dried to the point of shattering.
Edamame seedpods at the dry harvest stage.
Much of the high-value conventional edamame seed harvest in Asia is done with the crop standing at or near this stage. This is possible largely through the use of synthetic desiccants that are sprayed on the crop to dry the foliage several days before the crop is combined directly. This enables the pods to be easily threshed without green foliage interfering, as the combine is able to break the dry foliage into small pieces that are easily winnowed out during the threshing process. At the time of this writing the best edamame harvest method for organic production is currently used by several pioneering organic seed growers in southern Idaho and is closer to the methodology used with common bean (with a couple of notable twists).
In organic edamame seed production the initial step in harvesting requires undercutting the plants as described for common bean. Because losing seed due to shattering is the main concern during harvest, always complete this step in the morning to take advantage of the moisture on the pods from the morning dew. Next, instead of mechanically raking the cut plants into windrows, it is preferable to manually lift or fork the plants onto a porous agricultural fabric like Reemay or landscape cloth for curing. This cloth, which is rolled out in strips at regular intervals in the field, will catch seed from any pods that shatter when moved and during the curing process. Use of a porous material is recommended in case of rain during the 10 to 14 days that are required for curing the crop, as any moisture will easily drain away from the crop. The expense of the material is justified to offset what can be heavy losses in seed yield during the curing of the edamame seed.
Threshing the seed is best accomplished by gently forking the cured piles into a stationary thresher in dry weather to minimize losses. Edamame seed is more easily damaged during threshing and cleaning than most of the other legume seed crops. Therefore, threshing should be watched closely and adjusted early in the process so that the rotors do not cause splitting of the seed as it is threshed.
An edamame field trial.
Genetic Maintenance
Phenotypic differences for foliar and flower traits between edamame varieties are usually subtle and not easily distinguished until a grower has experience with a variety. Differences in the timing of pod ripening and the ability of a pod to stay green during ripening do vary from one variety to another. Selection for uniform pod ripening and roguing of any off-colored pods during the ripening process is important, especially when finding yellowing pods in varieties that have pods that usually hold their green color through their peak edible stage. As always, it is key to select for early vigor and overall health, roguing any diseased plants and becoming intimately familiar with what seems to be an ever-expanding profile of viral pathogens that affect soybeans.
Isolation Distances
Soybeans are highly self-pollinated with a crossing rate of less than 1% in most production settings. However, as with the other vegetable legumes, a number of environmental factors and genetic differences between varieties may contribute to increased cross-pollination. Therefore the recommended isolation distance between varieties to maintain a high level of genetic purity is 150 ft (46 m) in open terrain or 50 ft (15 m) when significant physical barriers separate varieties.
Fava Bean
The fava bean (Vicia faba L.) has been an integral part of the agriculture of the Mediterranean basin and the Near East for at least 8,000 years. These beans are now widely grown in temperate climates, most notably Western Europe and China. They are probably the most cold-hardy of the common vegetable legumes: Some varieties can withstand temperatures of 14°F (–10°C) during early vegetative stages of their life cycle. In warm temperate and subtropical areas they are grown as winter annuals, planted in autumn, putting on rapid growth and flowering in early spring, and harvested before the heat of summer. In cool temperate zones favas are planted early in the growing season, several weeks before the last frost, and grown as a summer annual, much like other vegetable crops of the Fabaceae.
The ‘Chak’rusga’ fava bean is a tall, prolific, multibranched, hardy, and drought-tolerant variety that comes from northern Bolivia.
Fava beans fall into two categories based on their use. The large-seeded type, which is often called broad bean, faba, or fava, is grown for its large, flattened, disc-shaped seed, which is 0.75 to 1.25 in (2 to 3 cm) long and is eaten fresh when slightly immature as a shell bean or is harvested at full maturity as a dry bean. The color of the large-seeded types varies from a buff or solid tan to a medium brown with darker spiral markings. The small-seeded form, which is grown as a cover crop, green manure, or fodder, is known by various names in English, including horse bean, tick bean, field bean, and bell bean. Its seed is 0.5 to 0.75 in (1.3 to 2 cm) in diameter, has an irregular round shape, and is mahogany brown to black in color. The widespread use of the small-seeded type as a green manure or cover crop is based on its ability to produce luxuriant spring growth and fix large amounts of nitrogen when overwintered in relatively mild temperate zones.
Fava beans are linked to a medical condition known as favism, an enzyme deficiency in humans that is an inherited trait among a small percentage of individuals of Mediterranean descent. People who eat favas that are deficient in a particular enzyme may suffer from a hemolytic anemia, which can cause death in some cases. It is therefore advisable for anyone of Mediterranean descent to always start with only a small bite the first time that you eat favas.
Crop Characteristics
Reproductive Biology
Fava plants stand upright and range from 2 to 6 ft (0.6 to 1.8 m) tall at full maturity. Stout, square stems bear pinnate leaves with flowers borne in clusters of two to four in the axils of the leaves. Flowers are 0.4 to 1 in (1 to 2.5 cm) long and have white petals with deep purple or black markings with all of the characteristic legume flower parts. Pods are inflated, are 3 to 8 in (7.6 to 20 cm) long, and usually produce three to four seeds. A large number of the flowers or young pods usually abort, and there is some speculation that presence of pollinators will increase the average number of pods that set on favas. While this species is considered to be primarily self-pollinated, there can be quite a bit of crossing with pollinator pressure. There is evidence that insects can be responsible for up to 30% cross-pollination in some locations.
Fava bean flowers (Vicia faba).
Climatic and
Geographic Suitability
Favas require cool-season conditions for best development. In hotter climates they are planted in the fall as a winter annual so that they can take full advantage of the moderate growing conditions of spring, flowering and developing seed before the heat of summer. In cooler climates, where daily high temperatures don’t regularly exceed 84°F (29°C), it is possible to grow a fava seed crop that matures in summer from a spring planting. As with other vegetable legume seed crops, it is desirable to have a seasonal dry period and lower humidity to ensure a lower incidence of seedborne pathogens.
Seed Production Practices
Soil and Fertility Requirements
Favas can be grown on nearly all soil types, though they seem to grow best on agricultural loams. They are more tolerant of acidic soils than other vegetable legumes. Available soil calcium is important, as with all Fabaceae crops, for maximum seed yields. Favas are one of the best legumes for their ability to fix nitrogen through their relationship with Rhizobium bacteria. Seed should be treated with the appropriate species of Rhizobium for this genus before planting, especially if you are planting on ground that hasn’t been used for fava production previously.
Growing the Seed Crop
Immature fava bean seedpod.
The fava seed crop can be planted in either of two seasons depending on your climate. If sown in fall to be overwintered, you must plant favas early enough to become well established before low temperatures and short daylengths curb growth. When spring-sown, it is important to plant as early as possible to ensure that flowering and seed development take place before hot weather arrives. Fall planting is desirable to help ensure an early seed harvest in regions where winter temperatures don’t usually drop below 14°F (–10°C).
Large-seeded vegetable fava types should be planted at a depth of 2 to 4 in (5 to 10 cm), while smaller-seeded bell bean types can be planted at half this depth. Favas are usually drilled with row spacings that are 22 to 28 in (56 to 71 cm), and 4 to 6 in (10 to 15 cm) between plants within the row. In Europe seed crops are sometimes planted in double rows that are 10 in (25 cm) apart and are separated from the next pair of rows by 24 to 28 in (61 to 71 cm). Cultivation can be practiced early in the season in a similar fashion to the method described for common bean (see Common Bean, “Growing the Seed Crop”) but can only be done early in the growth of the crop, as the stems of the fava plant are easily damaged, resulting in lodging.
Seed Harvest
Maturation of the fava seed crop is first accompanied by a darkening of the pods, which slowly blacken in color. This is followed by a drying and loss of sponginess in the characteristically thick fava pods. Watch the lower-setting pods closely; they will mature first and can shatter if you wait for the later-setting, upper pods to fully mature. You must cut the crop when the upper pods are fully formed but less than fully ripe. Swathing the crop should be done during cloudy, cool weather or early in the morning when shattering can be minimized. Mechanically raking the crop into windrows should follow the same protocol. Smaller growers in Northern Europe traditionally place the crop into shocks for the final drying before threshing. Threshing is easily done with a stationary field thresher or a bean combine that has been adjusted for the large seed size of the vegetable favas.
Genetic Maintenance
Selection and maintenance of key agronomic traits for overall health and vigor is always desirable. Maintaining uniformity of plant stature (bush versus vine) and general morphological traits is important; variation of any of these traits could be an indication of an unwanted outcross between different varieties. Because of the propensity of this species to cross-pollinate, growers should be especially vigilant in monitoring for plants that are the result of these crosses. Variations in seed coat color and seed size are probably the two most easily recognized traits that indicate probable outcrossing between fava bean varieties in a previous generation.
Isolation Distances
In the Fabaceae, fava beans are second only to runner beans for their degree of promiscuity, and therefore require a fairly large isolation distance. Informed organic seed producers prefer to treat them conservatively, as they know how many insect species will visit their flowers. For this reason they will separate varieties of this species by a minimum of 0.5 mi (0.8 km) in open terrain, with a 0.25 mi (0.4 km) minimum distance if physical barriers exist between production fields. This is the sensible recommendation for isolation of a crop that is so influenced by insect activity in its pollination.
Garden Pea
The garden pea (Pisum sativum L.) is one of the oldest cultivated pulses. N. I. Vavilov, a Russian ethnobotanist, recognized four centers of origin for this crop spanning an area from Central Asia through the Mediterranean basin to Abyssinia, indicating that the dissemination of pea germplasm must have occurred early in the spread of agriculture. Among the pulses the pea is one of the most widely grown species on Earth. Various forms of the crop are used as a vegetable, fodder, and green manure; its dry mature seed is used for soups and stews. The vegetable forms include: (1) shelling peas, which have well-developed, immature seed that is “shelled” from the pod when still soft and succulent; (2) snow peas, which have edible, fiberless flat pods that are harvested when the seed begins to swell; (3) snap peas, which have thick-walled, edible, fiberless pods much like snap beans and which are harvested when the peas are swollen but still succulent; and (4) pea vines, which includes the young shoots, with tendrils and sometimes flowers that are used in Asian-style stir-fry dishes and as a garnish.
While these vegetable types are grown seasonally in many diverse climates around the world, peas are best adapted to environments with a relatively cool growing season, especially for seed production.
Snap peas are a new version of an ancient crop with seeds that can be more fragile during harvesting and threshing than some of the older forms.
Crop Characteristics
Reproductive Biology
Peas are self-pollinated annuals with a short, intermediate, or long indeterminate vine growth habit. Short vine or dwarf varieties may be 2 ft (0.6 m) tall or less with a concentrated fruit set, while the taller indeterminate types can easily reach 6 ft (1.8 m) and bear over a longer season. Pea flowers are characteristic of most species of the Fabaceae as described under the “Reproductive Biology” section of the Fabaceae family introduction. The pistil of each pea flower contains a single carpel and a single ovary, which may bear up to 13 ovules attached to two adjacent placentae that occur along its length. A sticky, bearded stigma is receptive to pollen for several days before the maturation and release of pollen: However, the petals of the pea flower are usually tightly closed during this period and only open 24 hours after fertilization. While the petals of the pea flower are usually tightly closed during this period, this is when peas are most apt to cross if pried open by an insect species with this ability. There are several species of insects that can cross-pollinate leguminous flowers by cutting through the petals to access pollen and nectar before self-pollination has occurred. While the incidence of cross-pollination is usually well below 1% in most seed production areas, there are areas with a wide diversity of pollinator species present that may have much higher outcrossing rates in this crop. This may be the case in many organic production fields, especially on farms with diverse cropping and close proximity to native ecosystems.
A purple-flowered pea (Pisum sativum). Pea flowers can either be purple or white.
Climatic and
Geographic Suitability
Production of pea seed is best accomplished in regions with cool, moist spring weather that gradually turns warm in spring. The availability of ample moisture early in the growing season enables the crop to establish a vigorous, fully grown plant by the onset of flowering, which supports a bountiful pod set and seed yield. Peas are adapted to a moderate climate for both their vegetative growth and the development and early growth of the seed crop. In early spring the pea plant is sensitive to frost once blossoms and flowers are present. Exposure to temperatures above 84°F (29°C), especially during anthesis, fertilization, and early endosperm development may interfere with normal seed development and lower seed yields. Hotter summer weather is acceptable after the seed is fully formed—during seed maturation and harvest.
Pea seed produced in areas with a seasonal dry period during seed maturation and harvest has a much better chance of being free of seedborne pathogens and blemishes. Seed production areas that produce the highest-quality seed have a lower incidence of destructive pathogens and insects. Several serious insect pests of peas—including pea aphids, pea borers, pea leafminers, pea weevils, and thrips—are usually less persistent in these western valleys, although the incidence of damage from the pea weevil has greatly increased since North American pea seed production first moved to the West after World War II. Seed production areas in North America include portions of the Snake River Valley of southern Idaho, the Columbia Basin of eastern Washington, and interior valleys of southern British Columbia. The seasonal dry weather and low humidity in these locations at the time of harvest greatly enhance the quality of the crop.
As a major international crop, appreciable quantities of pea seed are grown in a large number of areas around the globe. In Europe commercial pea seed is produced in parts of the United Kingdom, the Netherlands, Denmark, Germany, France, and Spain. Commercial seed is also grown in Poland, Hungary, Russia, and Greece. Peas are grown widely in the Indian subcontinent, with large-scale commercial seed production in India and Pakistan. Much of the enormous quantities of pea seed used across China and Southeast Asia is grown locally, with commercial production in Thailand, Taiwan, and China.
Seed Production Practices
Soil and Fertility Requirements
Peas are grown on a wide range of soil types, from lighter sandy and silt loams to heavier clayey soils, but any soil must be well drained to minimize the chances of root rot organisms, which can cause crop losses. As with all legumes, peas are best grown on soils with a good, balanced fertility that do not have an excess of nitrogen. This is especially true in producing the seed crop, where excess foliar growth will only be a detriment in the early and even maturation of a superior seed crop. Compost or well-composted manure should supply plenty of fertility, especially if the ground has a good long-term program for adequate phosphorus, which is a must for good legume seed yields.
Inoculation with the proper nitrogen-fixing Rhizobium species should be done the first time you grow a pea crop in a particular field. After that, however, further inoculation may not be necessary as long as you grow another pea crop in the crop rotation within the next several years.
Growing the Seed Crop
The pea seed crop should be planted in spring after the threat of severe freeze has passed. While young pea plants are quite cold-hardy, a heavy freeze can damage the apical growing points of the young shoots. Early plantings also run the risk of suffering losses from damping-off organisms under prolonged cold, wet conditions. Therefore many experienced growers will not plant the crop as early as possible, which is often recommended. However, planting must still be done early enough for the crop to complete flowering and early pod formation before hot temperatures occur. In most pea seed production areas of the Intermountain West (eastern Oregon and the Palouse region of eastern Washington and northern Idaho) the crop is planted in mid- to late April, but it can planted in late March to early April in the warmer areas of the Columbia Basin of Washington and in both the Treasure Valley and Magic Valley of southern Idaho.
Pea seed can be planted at a depth of 1 in (2.5 cm) or less if steady, even moisture is the norm in spring. A shallow planting depth will help promote quick seedling emergence and a healthy stand if cold, wet conditions persist. Deeper plantings of up to 2 in (5 cm) can be used if the crop is grown on lighter soils and if precipitation is erratic in spring before irrigation is in place.
Pea seed crops have been grown in the western United States using either a row-cropping method similar to common bean or by planting the seed with a grain drill at 7- to 8-in (17- to 20-cm) centers where they eventually produce a solid closed canopy that is harvested standing, without swathing or windrowing. The latter method is not suited to organic production, as it relies heavily on pre-emergence herbicide treatment. Also, for organic culture it is essential to cultivate at least two to three times before the pea plants sprawl and flower. The close spacing used with the solid canopy method hinders many cultivation possibilities.
◀ Fully mature pea pod ready to be threshed.
The planting specifics for organic pea seed production are very similar to the methodology described for common bean, using the same 22 in (56 cm) row spacing but with a higher within-row density of 8 to 12 seeds per 1 ft (30 cm), or one seed every 1 to 1.5 in (2.5 to 4 cm). Seeding rates may vary according to type, although in pea seed production the recommended spacings are quite similar for the dwarf and vining types, as vining varieties are grown without trellising. Dwarf types can be grown at the higher end of this density of 1 seed/in (1 seed/2.5 cm) and vining types at 1 seed/1.5 in (1 seed/4 cm). While cultivation can be done in much the same way as you would for common beans, the earliest “blind cultivation” that is done after planting and before the crop emerges is often not as effective as it is in beans. This is because peas are planted earlier in the growing season than beans, and the earliest flush of weeds frequently only emerges with the warm spring days that also bring the pea seedlings out of the ground.
Seed Harvest
The pea seed crop is ready to harvest when a majority of pods develop a lighter color that is either yellow or light brown, and when they develop a rough, leathery appearance. The crop is then swathed and the plants are cured in windrows. In the western United States pea seed growers use pea lifters that are attached to the swather and hold the crop off the ground as it is cut. This minimizes damage to the crop and is best accomplished in the morning when the dew is still on the ground. Curing usually takes 7 to 10 days, or until the plants are completely dry and easily threshed. The windrows are then threshed with a grain combine using a pickup attachment, or the crop can be manually fed with pitchforks into a stationary combine. The spacing of the cylinder and speed of the rotor should be closely monitored to minimize damage to the seed.
Genetic Maintenance
Selection for seedling vigor, speed of emergence, and overall health of seedlings is always desirable, especially in a crop like peas, which is often planted during cold, wet periods that can cause the crop to languish both before and after emergence. Routine selection for the strongest seedlings will definitely improve these traits over generations of selection.
‘Oregon Giant’ is a popular disease-resistant variety of snow pea that produces prolifically over an extended season.
Peas have several key traits that should be observed when monitoring the crop for varietal integrity. Roguing should be done at an early vegetative stage, at flowering, and at full pod development. Leaf shape, size, and color can vary considerably, and variants should be eliminated before flowering. The size, color, and position of the flower on the plant can vary, as can the size, shape, color, and curvature of the pods, and off-types for these traits or other noticeable variants should be rogued. Another common pea off-type that may appear has the colorful moniker rabbit-eared rogue. The rabbit-ear rogue is best described by its leaves, which are smaller and narrower than the leaves of almost all commercial pea varieties of the past 100 years. It also is usually a more rangy plant that is taller, spindlier, and later flowering than most named pea varieties. These can usually be detected before flowering and possible crossing can occur, which is always desirable.
Isolation Distances
As with all self-pollinated vegetable crops in the Fabaceae, there are a number of environmental factors and varietal variations that can lead to cross-pollination in peas. While peas are usually highly self-pollinated, crossing less than 1% of the time in climates that are conducive to seed production, they can also cross to the extent that the recommended isolation distance of 150 ft (46 m) in open terrain is appropriate to maintain a high level of varietal purity. When barriers, natural or artificial, are present (see chapter 13, Isolation Distances for Maintaining Varietal Integrity), it is still advised to maintain at least 50 ft (15 m) of isolation to minimize crossing. In some areas where crossing has been noted to be significantly less than 1% between adjacent pea varieties grown for seed, growers have planted several rows of a taller unrelated crop to keep them isolated from potential insect pollination or mixing at harvest.
Importantly, the threat of mechanical mixing in a round-seeded crop like peas should not be dismissed. Mechanical mixing between two different varieties can always present a problem during harvest when self-pollinated crops have been planted in adjacent plots with no isolation breaks or natural barriers. Mechanical mixing can also happen when harvesting and seed-cleaning equipment is not thoroughly cleaned between any step in harvesting or processing different varieties of the same crop (see chapter 17, Stockseed Basics). However, with round-seeded vegetable crops like peas, edamame, or the small, round seed of the brassicas, it is possible for mixing to occur in seed-cleaning facilities, sheds, or any other space where seed is cleaned, conditioned, or bagged. The fact that round seed can easily roll across a table, floor, or any work surface means that seed from one lot can end up on the other side of the room near another lot by rolling from one place to another. Many experienced seed workers will acknowledge the fact that this has certainly been the cause of countless genetic mixes through the years. Therefore, anyone coming into seed growing should heed the well-worn phrase of old-timers in the seed business: “Seed on the ground, leave it down!”
Lima Bean
Lima beans (Phaseolus lunatus L.) are native to the northern reaches of South America, where they have been cultivated for at least 7,000 years. They were extensively cultivated in the coastal valleys and western central area of what is modern-day Peru when the European explorer Francisco Pizarro first collected them in the area that would become known as Lima. The limas originally from Peru are the larger, thick-seeded variant of the modern crop and historically known as the Potato Lima type in North America. This type quickly spread across the globe, although its use never rivaled that of the hardier common bean (P. vulgaris). This type of lima is one of the oldest cultivated crops of the New World.
The small-seeded or Sieva type of limas were domesticated from wild ancestors of the crop only 2,500 to 3,000 years ago in what is now southern Mexico and Guatemala. These small-seeded types produce the popular butterbeans that are ubiquitous in the southern United States. Unfortunately, both these and the larger-seeded types have gotten an unfavorable reputation in most of North America in modern times, as they have been grown as a dry bean, harvested on a large scale and eaten as a rather pasty mush by most people. The real treat that makes this crop such an outstanding vegetable among the initiated is the fresh-shelled, bright green, sweet and nutty beans that are picked and eaten long before the pods turn yellow and the seed gets starchy.
Crop Characteristics
Reproductive Biology
Limas are self-pollinated annuals with a determinate or indeterminate growth habit. Determinate or dwarf varieties may be 2 to 3 ft (0.6 to 0.9 m) tall with a concentrated fruit set, while the taller indeterminate types can easily reach 6 to 10 ft (1.8 to 3 m) tall and bear over a longer season. Lima flowers are characteristic of most species of the Fabaceae as described under the “Reproductive Biology” section of the Fabaceae family introduction. The flowers are borne on racemes that are 2 to 4 in (5 to 10 cm) long, and even under the best environmental conditions only a minority of the flowers set and produce pods. Anthesis has been reported to occur early in the morning. Limas are notoriously fickle in setting seed, as they are real heat lovers and probably suffer from inadequate fertilization of the ovaries when environmental conditions are not just right in the morning hours after anthesis.
As with many other legumes, limas have a sticky, bearded stigma that is receptive to pollen for some period of time before its maturation and release. While the anthers surround the style and stigma, there are times when the stigma will project out past the end of the keel petal, especially when insects land on the wing petals. This usually happens after pollination has taken place, but if it occurs before the pollen has been shed, then there is an opportunity for cross-pollination from an insect visitor. Limas have white to cream-colored flowers and have nectaries that secrete a high-quality nectar, both of which are known to attract a variety of pollinating insects, including honeybees, bumblebees, assorted wild bees, and many types of butterflies. Several studies have shown that insect visitation during pod set increases the number of pods, beans per pod, and total seed yield. This appears to be just another case where insects can increase the overall amount of seed set in self-pollinated crops by stimulating the effectiveness of pollen shed through physically moving the flowers.
Climatic and
Geographic Suitability
Lima bean is a tender warm-season crop that requires warm, well-drained soils for germination. The optimum soil temperature for vigorous germination is 85°F (29°C), and soil temperatures below 65°F (18°C) can encourage root rot. Ambient temperatures of 70 to 80°F (21 to 27°C) are preferred for optimum growth of the lima crop. Temperatures below 55°F (13°C) or above 90°F (32°C) during flowering may adversely affect pod set and seed yields. Lima beans require a longer season and warmer climate than common beans to mature their seed crop. Limas routinely require a minimum of anywhere from 110 to 140 frost-free days to produce a satisfactory commercial seed crop, with pole types generally requiring a longer season. For this reason much of the lima bean seed produced in North America has long been produced in the warmer interior valleys of California, with some of the earlier-maturing varieties grown in the seed production valleys of southwestern Idaho. However, growers must be careful in choosing the warmer-season climates in places like the Central Valley of California, as higher temperatures during flowering can reduce pod set and subsequent seed yield.
Seed Production Practices
Soil and Fertility Requirements
Soil conditions and fertility requirements are the same as those recommended for common bean (see Common Bean, “Soil and Fertility Requirements”). The main difference is that lima seed needs to be planted into soils at least 5 to 10°F (3 to 6°C) warmer than is needed for planting common bean (see “Climatic and Geographic Suitability”). This means that in many regions lima seed is planted a full 10 to 14 days later than common beans, ensuring that soils are sufficiently warm for rapid germination. Also, planting into moist soil is preferred to irrigating the crop after planting, both to minimize soil crusting and to minimize the chances of rotting the seed before emergence. If you’re growing lima beans in a particular field for the first time, then inoculating the seed with the appropriate Rhizobium species is recommended.
Growing the Seed Crop
As most commercial lima bean varieties are bush varieties and have a stature and form a canopy much like most common bean bush varieties, it is suggested that you plant and cultivate the crop per the recommendations for bush-type common beans (see Common Bean, “Growing the Seed Crop”). However, you can plant bush limas at a wider spacing between rows in climates where there is some concern of getting enough heat to mature the crop. Also, a wider spacing can accommodate some of the larger bush lima types, which can produce quite a canopy under ideal conditions. Between-row spacing for limas can be anywhere from 22 to 36 in (56 to 91 cm). The within-row planting density should be no more than six to eight plants every 12 in (30 cm).
Pole lima varieties require a much wider spacing, with rows at least 36 to 60 in (91 to 152 cm) apart and with a 4 to 8 in (10 to 20 cm) within-row spacing between plants. Large-scale seed production of many pole or vining type of limas is generally done without staking or trellising the plants.
Seed Harvest
As with all Fabaceae crops, proper timing of harvest is important in order to produce high-quality seed that is fully mature, has a high germination percentage, and has maximum storage potential. Each lima variety and type has its own specific harvest timing, though there are basic signs that indicate maturity. The initial sign for all beans that indicates a crop is approaching maturity is the color of the pods as they are breaking, or after they have turned yellow and are turning mahogany or buckskin in color, but before they dry completely to a light tan or brown and the pods become papery thin. Maturation to the brown, papery stage increases the danger of seed shattering during harvest. Pods should generally be yellow to buckskin at harvest in order to mature properly in the windrow, but the exact desired color may be variety-specific.
The crop should be cut when approximately 70 to 80% of the pods on the crop are of the desired color and point of breaking. The stems of the crop are undercut mechanically just below the soil surface and left in place for a day. The next day the plants are raked into windrows. Depending on weather conditions, the windrows should cure in the field for at least 10 to 14 days, with a possible turning of the rows near the halfway point. Threshing of limas is best accomplished during the heat of the day, as is done with other beans, when the pods are brittle and easily cracked. Seed should then be further cleaned to separate it from any plant debris that may be moist. If the seed is not sufficiently dry it may require air- or kiln-drying before being stored for a final cleaning and conditioning. Physical mixing of seed varieties can be a source of variety contamination. Thoroughly clean out harvesting and cleaning equipment between working with different varieties.
Genetic Maintenance
There are very few stages in the growth of most legume crops in which genetic differences within a variety are readily apparent. If you are able to establish a uniform stand, then it is possible to perform selection for speed of seedling emergence, seedling health, and overall vigor: all essential traits for organic production. If you routinely rogue out late-emerging, low-vigor seedlings, you’ll see improvement over cycles of selection for these traits and improvement in the overall seedling vigor of the variety. Many growers of legume crops can identify obvious differences that might appear in pod characteristics, flower color, and presence of runners, but other, more subtle plant characteristics may only be apparent to experienced farmers who specialize in the crop and know a specific variety. For some traits, like leaf shape, color, and plant stature, it is possible to evaluate the plant and rogue it to type before flowering has begun. Flower color, placement, and the timing and duration of flowering can all be selected during flowering. Pod characteristics such as color, shape, and length are also notable to the experienced grower and can be selected. Additionally, it is critical to rogue for disease in all bean crops in order to produce quality seed, minimize the risk of seedborne diseases, and select or maintain a variety’s disease resistance.
Isolation Distances
While lima beans are considered highly self-pollinating by most commercial seed producers, they have been reported to outcross at a higher rate in some environments than the common bean (P. vulgaris). This may be due to the unique morphological characteristics of the stigma being exposed and the higher nectar content than is found in some of the other Phaseolus species (see “Reproductive Biology” in the Fabaceae introduction). For this reason, many researchers recommend increasing the minimum isolation distance between two lima crops over what is recommended for common beans.
Because my isolation recommendations uphold a very high standard for all of the highly self-pollinating crops of the Fabaceae (including common bean, garden pea, and edamame), the minimum isolation distance recommendations for lima beans of the same horticultural type do not need to be higher than what I am recommending for these crops.
As with the other largely self-pollinating species of the Fabaceae, it is appropriate to observe the minimum 150 ft (46 m) isolation distance if you’re growing more than one lima variety of the same type in open terrain with no natural barriers to ensure a relatively high level of genetic purity. If you are producing multiple lima crops of different horticultural types (say, a small-seeded Sieva type versus a larger Potato Lima type or a bush type versus a vining type), then it is recommended that you produce these a minimum of 300 ft (91 m) apart in open terrain.
If you’re producing multiple lima bean crops in areas with natural barriers between crops (see chapter 13, Isolation Distances for Maintaining Varietal Integrity), then the minimum isolation distance needed between two limas of the same type can be dropped to 75 ft (23 m). For two different lima types with a substantial physical barrier between them, then the isolation distance should be increased to 150 ft (46 m).
It should be noted that these recommendations are based in large part on information from seed production areas in North America. If lima seed is produced in more tropical regions, especially in areas with both the kind and breadth of insect biodiversity that is present in the ancestral homeland of the various forms of this crop (southern Mexico, Guatemala, or northern South America), then it may be necessary to reassess these minimum isolation recommendations and increase them to maintain varietal purity.
The runner bean (Phaseolus coccineus L.) is a warm-season legume native to high-altitude regions of Guatemala and southern Mexico. It is a vining herbaceous perennial with a large tuberous root that is usually grown as an annual. In temperate climates with only light frosts, runner beans may regrow for a number of seasons from these perennial roots. It is prized for its large showy flowers, its flavorful immature pods, and the shell beans that are harvested when the beans are well filled but still immature and succulent. The indigenous people of Central America, who have cultivated runner beans for at least 2,000 years, utilize both the large, fleshy roots and the dried beans in their diet. There are reports that the roots may contain toxins and require special preparation if they are to be used as food.
Runner beans have become very popular as an ornamental in the United States and Europe because of their attractive flowers, which range in color from bright shades of scarlet or crimson to a cream white. Robust vines easily reach from 12 ft (3.7 m) to as much as 16 ft (5 m) in length and may have hundreds of blooms at their peak. Europeans also favor runner beans for the unique flavor of the immature pods, which are eaten like snap beans. Dwarf or true determinate varieties have been developed for the culinary markets of Europe.
Crop Characteristics
Reproductive Biology
While runner beans have perfect flowers that are much like standard Fabaceae blossoms in form, they are probably the most promiscuous of the vegetable species of this normally self-pollinating family. This species certainly has blossoms that are very attractive to a number of pollinators, with individual flowers measuring almost 1 in (2.5 cm) across. These flowers are borne in clusters with upward of 20 blossoms on a single raceme. This attracts a diversity of pollinating species, from hummingbirds to honeybees, bumblebees, assorted wild bees, and many types of butterflies.
Indeed, this species has co-evolved with pollinators. Unlike most other legumes many runner beans are unable to self-pollinate unless a pollinator lands on the wing petal and “trips” the flower. This causes the stigma and anthers to extrude through the keel, allowing pollen to reach the stigma and self-pollinate the flower. A number of breeders have noted a marked reduction in yield in runner beans when pollinators are artificially excluded from the plants during flowering. For optimum conditions for seed production it is advised that growers ensure that a large number of honeybees or bumblebees are present to adequately visit the plants during flowering.
Another important issue in growing runner beans is the fact that pollen is often deposited on the abdomen of pollinators during the tripping of the flowers, thereby increasing natural cross-pollination. Jim Myers, a bean breeder at Oregon State University, has found that the rate of cross-pollination among runner bean varieties is “highly variable” and reports that rates of crossing up to 50% per generation are not uncommon in temperate climates, when different varieties are grown in close proximity. Researchers in the tropics have witnessed crossing rates as high as 87% with native pollinators. Many seed growers who have grown more than one type of runner bean in close proximity have also reported crossing between varieties far above acceptable levels for commercial production. Because insects are integral to the pollination of this crop, the isolation distances must be increased significantly over the standard distances set for most self-pollinated legumes (see the “Isolation Distance” section).
Climatic and
Geographic Requirements
Runner beans are a warm-season legume and need a minimum of 110 to 120 frost-free days to produce a satisfactory commercial seed crop. Runner bean varieties grown in higher latitudes are day neutral in their flowering response and are most prolific in setting fruit during hot weather with summer daytime temperatures in excess of 86°F (30°C). The types grown in the tropics are short day plants in their reproductive response. A seasonal dry period for seed maturation and harvest is desirable for all types to minimize any rot or seedborne pathogens.
Seed Production Practices
Soil and Fertility Requirements
Soil conditions and fertility requirements are the same as those recommended for garden peas (see Garden Pea, “Soil and Fertility Requirements”). If you’re growing runner beans in a particular field for the first time, then inoculating the seed with the appropriate Rhizobium species is recommended.
Growing the Seed Crop
As with other bean crops, seed of runner beans is tender and should only be planted when soil temperatures are above 65°F (18°C). Most runner bean varieties have a vining habit, and many small-scale specialty producers in North America trellis their crop with much hand labor. Trellised crops are routinely planted at 5 ft (1.5 m) row centers with a 6 to 8 in (15 to 20 cm) within-row spacing. Larger scale seed productions of vining types in Europe are grown without staking. Bush runner bean varieties grown for seed are planted at 3 ft (0.9 m) row centers with 8 to 12 in (20 to 30 cm) spacing within the row due to their large bush frame.
Seed Harvest
Seed of bush-type runner bean varieties is harvested in a similar fashion to bush snap bean harvest (see Common Bean, “Seed Harvest”). For seed production of vining types grown without trellising, the use of pea lifters attached to the swather is necessary to prevent excessive cutting and shattering of mature pods when swathing the crop. In addition to lifters, one also needs vertical shears on each end of the cutter bar since vines intertwine and form a continuous sheet at harvest. The crop is then placed into windrows and cured for 7 to 10 days (weather depending) before threshing and cleaning. Cutting and threshing is best done in the morning, when the moisture from the dew helps prevent excessive shattering.
A number of small-scale US seed producers of the vining types do trellis the crop. The advantage over allowing them to sprawl on the ground is that there is usually very little rot associated with the drying pods; however, stripping the vines from the trellis is both time- and labor-intensive. Vines should still be cured in windrows before threshing. Take care to set the speed and spacing of rotors of the threshers, as with all large-seeded legumes, in order to not damage seed.
Genetic Maintenance
Selection and maintenance of key agronomic traits for overall health and vigor is always desirable. Maintaining uniformity of plant stature (bush versus vine) and general morphological traits is important; variation of any of these traits could be an indication of an unwanted outcross between different varieties. Because of the propensity of this species to cross-pollinate, be especially vigilant in monitoring for plants that are the result of these crosses. Variations in flower color and in seed coat color are probably the two most easily recognized traits that indicate probable outcrossing between different runner bean varieties in a previous generation.
The most common flower color of runner beans is scarlet, although there are variants in the shade of this color in the petals of different scarlet runner varieties. The second most prevalent flower color of this species is white. If crosses occur between a scarlet-flowered type and a white-flowered type there are two different outcomes in detecting the outcrosses, depending on which of the two populations you monitor in the subsequent generations. (Note: Flower color in runner beans is a qualitative, simply inherited trait similar to the qualitative traits Mendel used in his classic work with peas that laid the foundation of modern genetics. Hence, a review of Mendel’s work with monohybrid crosses from any number of high school or college biology texts may be of value in understanding this information on roguing based on flower color.)
If you grow the seed of the scarlet-flowered variety after an outcross with a white variety there will be no indication in the next generation that the white flower trait is in the scarlet population. This is because the white petal color trait is genetically recessive to the scarlet petal trait (or any other pigmented petal shades that occur in runner beans). The white trait will only be expressed again in the following (F2) generation when 25% of all progeny resulting from any initial crosses between the two types will have two copies of the white color gene and have white flowers. While these plants with white flowers are easily rogued from a scarlet-flowered population, there will be twice as many plants where the white petal gene is in the heterozygous state and is not expressed. Through normal segregation of the genetic material there will always be a percentage of the plants in this scarlet population with the white flower gene in the heterozygous recessive condition that you will be unable to detect (and unable to rogue) through a normal visual inspection. In this case the best solution is to return to a stockseed lot of the scarlet variety or perform a controlled progeny test (see chapter 17, Stockseed Basics).
Alternatively, when you grow the white-seeded runner bean variety after it has outcrossed with a scarlet-flowered variety you will be able to easily identify the plants that have resulted from cross-pollinations with the scarlet type. Because the gene for scarlet flower color is dominant, it will be expressed in all progeny of these outcrosses in the first generation after the cross. Therefore, by eliminating all of the scarlet-flowered plants you will completely rid the white variety of all plants that resulted from the outcrosses with the scarlet variety. With a dominant gene for a simply inherited trait crossing into a new population, “what you see is what you get!”
The seed coat color of the scarlet-flowered types is a mosaic of purple and black; the white-flowered runner beans have a pure white seed coat. The inheritance in crosses between these two types seems to follow exactly the same pattern as the corresponding flower color trait.
Of all of the vegetable crops of the Fabaceae, runner beans may be the most promiscuous, and therefore they require the largest isolation distance. Indeed, a number of seed producers prefer to treat them as if they are cross-pollinated crops and separate varieties of this species by a minimum of 1 mi (1.6 km) in open terrain, with a 0.5 mi (0.8 km) minimum distance if physical barriers exist between production fields. This is the sensible recommendation for isolation of a crop that is so influenced by insect activity in its pollination.