Legumes

Legumes are nitrogen-fixing plants that produce many of the foods we eat.

Peas and beans are common legumes. Peanuts, chickpeas, alfalfa, clover, lentils, vetch, mesquite, carob, tamarind, lupins, wisteria, and soybeans are also legumes. The unique behavior that makes legumes so valuable is that most of them are able to convert atmospheric nitrogen into a form that is usable by other plants.

Nitrogen

Over 80% of our atmosphere is made up of nitrogen. Plants are greedy for nitrogen, but they can’t use atmospheric nitrogen. Some plants, our beloved legumes in particular, have developed mutually beneficial relationships with certain bacteria that live on or in their roots. These bacteria are able to combine atmospheric nitrogen with hydrogen to create ammonia, which is then converted into a usable form of nitrogen. This is called the Nitrogen Cycle and is what makes legumes an important part of crop rotation and cover crops. Some people claim that marigold plants interrupt the nitrogen-fixing ability of legumes, but I have not found any research to support those claims.

Wax beans

Legume plants​

With so many family members, it should come as no surprise that there is plenty of variety. Some legumes grow low to the ground in a spreading habit, while others vine, and other stand upright. All legumes are dicots, which means they produce two seed leaves before true leaves appear. It also means that the seeds tend to be made up of two halves. The fruit, nut, or seed of legumes is technically called a pulse. Pulses are grain seeds held within a pod, or simple dry fruits, that develop from a single carpel. Most legume seeds have a “zipper” along one side that opens up when the seed is ripe. This behavior is called dehiscence. These seeds are often rather large and fast-growing, making them an excellent choice when gardening with children.

Freshly dug peanuts (Pollinator) CC BY-SA 3.0

Legumes as soil amendment

Legumes can be used as a green manure, cover crop, or an edible harvest. When used as a green manure, plants are allowed to reach the flowering stage and are then cut and left where they fall to decompose. This returns valuable nutrients to the soil and improves soil structure. Other legumes are grown as a cover crop to prevent erosion. Most legumes have strong, deep roots that help aerate compacted soil.

Legume selection (USDA) Public Domain

Legumes as food

Legumes are a high protein, high fiber food source. Fava beans, wax beans, lentils, lima beans, and wheat are all just a few of the legumes we eat on a daily basis.

Pests and diseases of legume crops
While the pests and diseases of most legumes are more species specific, nearly all legumes are susceptible to Fusarium wilt. Bean mosaic and powdery mildew are common bean and pea diseases. Stinkbugs enjoy legumes and, what makes them worse is that they can also transmit tomato bacterial spot. Weevils and treehoppers are common pests of legumes.

Adding legumes to your garden or landscape can improve the soil, feed nearby plants, and they provide a delicious harvest. Give legumes a try!