What Plants are Legumes
Probably the most common legumes in home gardens are peas and beans of all kinds (snap, soy, lima, broad...), but this large plant family contains upwards of 16,000 species. We 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, like 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 we 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 actually fix the nitrogen, which the plants then take up. The Rhizobium do not hurt the plants; it's a symbiotic relationship.
You can actually see the nodules on the roots with your eyes. The photo at right 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.
Rhizobia are actually 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. We know they're delicious. It's a big bonus that they're healthy, too. They're low in fat, high in fiber, as well as being a good source of protein, calcium, iron, zinc, calcium, selenium, B vitamins and antioxxidants.