Most people know the edible legumes: soybeans, lentils, peanuts, chickpeas, black-eyed peas, black beans, white beans, green beans, lima beans, fava beans, and Asian yard-long beans, among many others. Carob and licorice are also legumes, and are considered by many to be edible. Other legumes, like alfalfa and clover, are used to feed livestock – and honeybees. Some trees are legumes, including redbuds, locusts, mesquite, and many tropical trees, such as tamarind. Finally, a few invasive species in North America, for example kudzu and wisteria, are legumes.
In addition to their worldwide use as food crops, legumes are critical for soil nutrition. Legumes are symbiotic hosts for rhizobial bacteria that live in root nodules and “fix” atmospheric nitrogen. That is, rhizobia convert nitrogen from a chemically inert form (N2, i.e. nitrogen gas) to a reactive form (NH3, i.e. ammonia) that can be metabolized by plants, animals, and microbes. Not only does this provide nitrogen for the legume itself, but it can boost the nitrogen content of the surrounding soil.
This article starts with a quick run-down of legumes commonly grown in home gardens. It will then cover how to sow legumes for best results. It’ll then discuss common diseases and insect pests of legumes and how to control them. Finally, it will touch on using legumes as soil-building cover crops.
Varieties
Peas (Pisum sativum): The peas belonging to this species originated in Europe. Examples include English peas/garden peas, snow peas, and sugar snap peas. Other legumes called “peas”, like chickpeas and black-eyed peas, are from different species and are covered below.
Peas are cool-season crops. This makes them a great candidate for early planting in Virginia. (That’s why we’re publishing this article in February!) Check out Virginia Tech’s planting schedule (PDF link) for target dates for spring sowing in your hardiness zone. Personally, I plant pea seeds in early March and they usually germinate by the end of the month. The seedlings can handle a mild frost, but if there’s a hard frost in April, I’ll cover them. Typically I’ll do just one round of harvest and pull up the plants in May, then grow beans in the same spot.
Southern peas, e.g. black-eyed peas (Vigna unguiculata var unguiculata): These peas have a lot of other names, like cowpeas, crowder peas, and cream peas. Originating in India or southern Asia, they were introduced to North America via the slave trade.
Southern peas are warm-season crops, so don’t sow until the soil has reached 60℉, around mid-May in piedmont Virginia. They will thrive in hot summer weather. Expect about 50-55 days until fresh peas can be harvested, and 65-75 days for dry peas.
Yard-long/asparagus beans (Vigna unguiculata var. sesquipedalia): These beans were probably bred in Southeast Asia. As the Latin name indicates, they’re closely related to Southern peas. Like Southern peas, they’re warm-weather crops, so plant in warm soil. They form long vines, up to 10 feet long. Support accordingly – or trim when they reach the tops of their supports.
Yard-long beans should be harvested before the seeds reach maturity. Pods containing immature seeds will look and feel a little puffy. As the seeds mature, they will swell and fill up the pods.
Chickpeas/Garbanzo beans (Cicer arietinum): Chickpeas aren’t a good choice for home gardeners in Virginia because they favor dry climates and sandy loam soil, and require a lot of space. Nevertheless, Penn State has a nice writeup on growing chickpeas at home.
Peanuts (Arachis hypogaea): A classic Virginia crop that originated in South America, peanuts grow best in light, sandy soil, a la southeast Virginia. The “Tennessee Red” variety, however, thrives even in the clay soils of the piedmont. That said, they will do better in soil that’s been amended with ample organic matter.
Peanuts are frost-sensitive and have a long growing season, 110 – 130 days. They transplant well, though, so a good strategy is to start them inside 4 weeks before planting outdoors. Wait until the soil has warmed to 60℉ before transplanting. As the plant grows, mound soil a few inches high around the base.
The growth habit of peanuts is fascinating. Peanut flowers self-pollinate, after which the end of the flower stalk elongates to form a structure called a “peg”. The peg droops down and penetrates the ground, where the peanut pod develops. It’s important to keep the plants well-irrigated (about 1” per week) as the peg elongates and develops. The peanuts will be ready to harvest after the foliage turns yellow in late summer or early autumn. A couple of weeks before harvest, stop watering the plants.
Harvest by pulling the whole plant out of the soil. Dry for a week in a warm spot with good air movement. Then cut the peanuts off the pegs and spread them out to cure for a few weeks in a cool, dry spot. Store in a cool, dry place, ideally in a mesh bag.
Consult the articles listed in the References section for more details about peanut cultivation.
“Common” bean (Phaseolus vulgaris): Originating in North America, these are the beans most gardeners are familiar with. There are two main types: pole beans, which require support for their vines, or bush beans, which can grow without support. Half-runner beans are in between; they don’t grow as tall as pole beans, but sprawl without support. Amongst these categories, there are many, many varieties, with diverse bean and pod sizes, shapes, and colors. Snap beans, like green beans, purple beans, and yellow or wax beans, belong to this species. So do black, white/cannellini, Great Northern, navy/Boston, kidney, and pinto beans. Personally, I usually grow good old Blue Lake pole beans.
How to support pole beans? One option is to run electrical conduit (or rope or wire cable) horizontally between the tops of fence posts at least 6 feet high (see picture below), then tie twine to the conduit and attach it to stakes or another piece of conduit on the ground. Plant the seeds in a line near the bottom of the twine. Another common method is to fashion a tripod from long sticks or pieces of sturdy bamboo. Plant the seeds around the tripod.
Common beans are warm-season crops, so wait to sow until the soil reaches about 60℉.
One important difference between pole and bush beans: pole beans “fruit” all through their growing season, whereas bush beans produce only for a short time, just a couple of weeks.
Lima beans (Phaseolus lunatus): Lima beans – named for the city – are famous for their buttery flavor. Growing them is not too different from “common” beans. Plant seeds once the soil has warmed up. They come in pole and bush varieties.
A caveat about lima beans is that raw limas contain small amounts of toxins called glucosides. Though the levels are low, it’s best to never eat raw lima beans. Cooking destroys these toxins.
Fava beans (Vicia faba): Somewhat notorious because the beans themselves are covered by a fibrous membrane that must be removed, one bean at a time, fava beans’ rich, nutty flavor is worth the effort. Some people make hummus with fava beans in place of chickpeas.
Fava beans, like peas, are cool-season crops and should be planted early in the season, i.e. the beginning of March in piedmont Virginia. Look for varieties that mature relatively quickly, from 75 – 80 days, because hot summer weather impairs pollination and makes the plants disease-prone.
Fava bean plants are 2 – 4’ high and are sturdy, not viny. They won’t need a trellis but might benefit from staking or a “Florida weave” support.
Soybeans (Glycine max): Soybeans are a great choice for home gardens in Virginia, particularly when they’re harvested young and eaten as edamame. (Boil pods for 7 – 10 minutes in salted water, then shell before eating as snacks or in salads.) Look for varieties that are bred for eating fresh, not dried. The plants are very productive: by one estimate, a dozen plants will yield enough for a family of four.
Plant soybean seeds once the soil has warmed to 60℉. The plants resemble bush beans and don’t need a trellis. Most varieties can be harvested within 80 days.
Sowing
Soil preparation: Most legumes can handle Virginia clay, but will perform better if the soil is well-drained. The best way to improve drainage is with organic matter, i.e. compost. A good rule of thumb is to work about 4” of compost into the top 12” of soil when preparing a new bed for planting. This is a lot of compost, and a lot of work, but the improved soil texture will be worth it. After the first year, consider the no-till methods that Piedmont Master Gardeners Fern and Cleve Campbell use in their home garden, as described by Ralph Morini.
Legumes grow best in mildly acidic soil, pH 6.0 to 7.0, but aren’t too picky about soil pH. That said, it’s always a good idea to have your soil tested to ensure that pH and nutrition levels are within reasonable ranges.
When amending soil, use fertilizer that’s low in nitrogen. (That’s the first number on the label.) This is because, as mentioned above, legumes (or, rather, their symbiotic rhizobia) fix their own nitrogen. Adding extra nitrogen will promote leaf and stem growth at the expense of flowers and fruit.
Spacing and depth: Follow the recommendation on the seed packet.
Timing: As discussed above, some legumes are cool-season crops and should be planted early, as early as the beginning of March in piedmont Virginia. Others are warm-season crops and shouldn’t be sown until the soil has warmed up to around 60℉.
Inoculation: Sometimes the nitrogen-fixing rhizobia need help getting started. You can encourage their growth by coating seeds with an inoculant before planting. This is especially important if you haven’t grown legumes in your garden before. These bacteria can be found at garden stores or online. Be sure to get the correct kind of inoculant, because different legumes host different rhizobia.
Pests and Diseases
Insect pests There are three main insect pests of legumes:
– Aphids, which suck nectar out of leaves and stems and can spread diseases. Control by knocking them off plants with a spray of water, or with horticultural oils like neem oil.
– Cutworms, which sever stems near the soil line. Control by inspecting your plants, and if necessary protecting the base of the plants with a collar made from aluminum foil.
– Bean beetles, which chew big holes in leaves (see photo). To me they look a lot like ladybugs, but with a red head, not black. Control by planting in rows where no legumes have been planted for the past two years. Delayed sowing can also help: over-wintering adults emerge in mid-May and will fly away if no seedlings are around. Minor infestations can be controlled by picking the beetles off plants.
Diseases Legumes can suffer from root rots, which can be prevented by maintaining good drainage in the soil as described above, and by not over-watering. Various bacterial and fungal blights can also affect legumes. These can be prevented by planting resistant varieties and by keeping plants properly spaced, to promote air movement and keep the leaves dry. If irrigation is necessary, water the base of the plant and don’t splash soil on the leaves. Finally, legumes can be infected by viruses. These are usually spread by insects, particularly aphids, so controlling infestations should keep plants virus-free.
These diseases are virtually impossible to cure, so prevention is the only way to keep your plants healthy. Consult the Virginia Cooperative Extension’s Pest Management Guide (PDF link) for more information.
Use as cover crop/green manure
Finally, legumes make a great cover crop that can boost the nitrogen content of soil. These soil-building cover crops are sometimes called “green manures”.
The choice of legume depends on when the cover crop will be planted. For summer planting, use warm-season legumes like Southern peas or soybeans. For planting in the fall, choose cold-hardy legumes like peas. Clover and alfalfa are classic cover crops; both germinate best at warm temperatures. It’s a good idea to also plant “tillage” radishes, to loosen dense or hard soil, and a fast-growing grass like annual rye, buckwheat, or oats, to add organic matter and suppress weeds.
Consult the articles in the Reference section below for more details about cover crops.
Final thoughts
Legumes are garden staples for many good reasons: they’re easy to grow, productive, and of course delicious. It’s nearly time to plant peas, and beans won’t be far behind. And hopefully this article will provide some inspiration to try growing a legume that’s a little off the beaten path. Enjoy.
References
Featured image: Serge96, Wikimedia Commons. License: CC BY-SA 4.0.
Arachis hypogaea (peanuts) North Carolina State Extension
Bean leaf beetle Iowa State University Extension and Outreach
Bean leaf beetles in home gardens University of Minnesota Extension
Chickpea Penn State PlantVillage
Cover cropping in Virginia (PDF link) USDA
Cover crops Cleve Campbell, Piedmont Master Gardener
Cover crops as nitrogen source Michigan State Extension
Edamame – a great addition to your garden North Carolina Cooperative Extension
Edamame: an easy crop to introduce to your vegetable garden University of Missouri Extension
A gardener’s guide to peas Penn State Extension
Green beans: How to grow it South Dakota State University Extension
Grow your own peanuts Jan Rhoades, University of California Master Gardener
Growing beans in home gardens University of Minnesota Extension
Growing cover crops for nitrogen on vegetable farms Penn State Extension
Home garden green beans University of Georgia Extension
Inoculating garden legumes University of Minnesota Extension
Is nitrogen fixation oversold with legume cover crops? Nebraska Institute of Agriculture and Natural Resources
Legume seed inoculants Colorado State University Extension
Long bean – an Asian vegetable emerging in Florida University of Florida, Institute of Food and Agricultural Services Extension
Peanut Clemson Cooperative Extension
Pest Management Guide – Home Grounds and Animals (PDF link) Virginia Cooperative Extension
Plant cover crops (PDF link) University of Maryland Extension
Recommended planting dates (PDF link) Virginia Cooperative Extension
Southern peas Clemson Cooperative Extension
Southern peas (Black-eyed peas) University of Arkansas Cooperative Extension Service
Vicia faba (fava beans) North Carolina State Extension
