Legumes are a huge family of plants, including a wide variety of common human food crops including beans, peas, lentils, and garbanzos. Important livestock crops including alfalfa and clover are also legumes.
Legumes are a critical part of any farm’s crop rotation. Unlike any other family of plant, they provide their own fertilizer through an evolved relationship with specific soil bacteria that colonize their roots. Those bacteria pull nitrogen from the air and “fix” it in the soil where the plants can access it.
You can actually see evidence of this process if you pull a leguminous plant out of the ground, in the form of small white “nodules” on their roots showing colonization by the bacteria.
The nitrogen pulled from the air allows legumes to generate the amino acids that become proteins in the seeds or beans the plants produce. If the beans or seeds are harvested, the nitrogen goes with them, but without reducing the existing amount of nitrogen in the soil.
On the other hand, if only the plant is harvested — as hay, for example — some of the nitrogen remains in the soil. Over time, a hay field can build a stockpile of nitrogen that will create a bank of fertilizer in the soil for the next crop to occupy that field.
And if the leguminous plants are not harvested at all, but rather grazed or plowed back into the field, the nitrogen fixed in the roots stays in the soil where it can benefit the next crop.
Terra Firma grows over a hundred acres of legumes each year on our 200 acre farm. That includes the Peas that we harvest for your CSA boxes in the spring as well as both summer and winter “cover crops” that are grazed by sheep. And of course, the Green Beans that are featured in your boxes today.
We grow Green Beans in the spring and harvest them for a few weeks in early summer, but it’s challenging to harvest them when it gets too hot. So we start planting again in July and continue until Labor Day.
October is peak Green Bean season here. The days are warm enough to keep the plants growing, and the cool nights ensure that the beans themselves are high-quality. But fall is a transitional season, and Green Beans are a finicky crop. Heavy rain knocks the plants down into the mud and can ruin the beans. And even a light frost will burn the foliage and cause the beans to blister.
More often than not, we lose at least one planting of Green Beans to either rain or frost. But that’s okay, because our entire fall bean planting serves a second purpose: as a cover crop for the spring crops that we will plant following them.
If we’ve harvested the beans first, we’ll fertilize the field with some compost — although not as much as we normally would. But if the beans go unharvested for any reason, we don’t need to fertilize.
I hope you enjoy the Green Beans in today’s boxes not just because they are tasty, tender and healthy — but because of their smaller environmental footprint.