A legume is a plant in the Fabaceae or Leguminosae family. The seed pods, or fruits, of these plants have two seams that run along the length of the pod, with multiple seeds attached to one of the seams, such as the peapod shown here. When the seeds mature, the seams burst open to distribute them. These dried legume seeds are sometimes referred to as pluses.
What Plants Are Legumes?
Probably the most common legumes in home gardens are peas and beans of all kinds (such as snap, soy, lima, broad, etc.), but this large plant family contains upwards of 16,000 species. People generally think of legumes as foods for humans or livestock. Although not all of them are edible, many are. Besides peas and beans, there are peanuts, lentils, carob, alfalfa, and clover. But some leguminous plants are grown simply as ornamentals, such as baptisia, lupins, wisteria, and locust trees.
What's so Great About Using Legumes in the Garden?
Legumes are often used as cover crops or mixed into lawn seed mixes because of their ability to fix nitrogen. Fixing nitrogen means converting pure nitrogen (N2), which plants and animals cannot access, into its ammonia form (NH3), which people can use. Bacteria are required to make this change and the nodules on the roots of legume plants are where Rhizobium, a soil bacteria, enter the root and start to multiply. It's the bacteria that fix the nitrogen, which the plants then take up. The Rhizobium does not hurt the plants; it's a symbiotic relationship.
You can see the nodules on the roots with your eyes. The photo here shows some nodules just forming. They are white or grey before they start fixing nitrogen, but they turn pink or red as the process gets underway. Perennial legume roots with older nodules on them can look like the fingers of a hand. On garden vegetables, they may get to the size of a pea. Some legumes fix nitrogen better than others. Green beans are on the low end, compared to peanuts, broad beans and soybeans.
The nitrogen doesn't disappear immediately after the plants die. That's why it is recommended you cut pea and bean plants at their base and leave their roots in the soil. Even after the top growth is gone, the nitrogen-fixing nodules continue feeding other plants.
Rhizobia are present in most healthy soils, but they don't tend to become active until the soil warms. Since peas are generally planted in cool, damp, spring soils, using an inoculant, a powder containing Rhizobia, is recommended to kick-start the process.
Despite their fancy, funny name, legumes are easy-to-grow plants that can be found in just about every backyard garden. Because there are multiple seeds in every pod and multiple pods per plant, legumes produce a good-sized harvest in a small space.
And they don't just feed the soil. Legumes are some of the most popular foods in the world. You know they're delicious. It's a big bonus that they're healthy, too. They're low in fat, high in fiber, and a good source of protein, calcium, iron, zinc, calcium, selenium, B vitamins, and antioxidants.
If You're Allergic to Peanuts, Are You Allergic to All Legumes?
You can be sensitive to the proteins in more than one type of legume, but most people are not. Your doctor will be able to test you for possible problems.
More on Growing Legumes in Your Garden
Few vegetables are as easy to grow and versatile in the kitchen. You can eat most of them either fresh or cooked, as a salad, side dish, or in the main dish. And if you grow them to dry, you can store them for months and enjoy your harvest at any time of the year.
How to Grow
- Nitrogen Fixation by Legumes
- Growing Legumes to Increase Soil Nitrogen