Cover Crops! Interplanting with Legumes

With summer drawing to a close, it’s time to start thinking about your winter garden, and that means cover crops! Here are some things to consider when planting your cover crops this year:

Normally, a gardener or farmer planning a crop rotation (over time) would start in the late autumn/winter/early spring season by planting a nitrogen-fixing legume, such as a cold-hardy fava (perhaps using the Banner* variety, which can fix up to 0.22 pounds of nitrogen and can withstand temperatures down to 10˚F) or the even hardier Woolly Pod Vetch*, which fixes up to 0.63 pounds of nitrogen/100 sq. ft. and can withstand temperatures to 0˚F., or the truly cold-loving Hairy Vetch*, which can withstand temperatures down to -25˚F. Then, in the following late spring/summer/early autumn, the farmer would plant a summer grain crop to take advantage of the nitrogen stored in the soil by the legumes the previous season.

A challenge with this rotation scheme is that the amount of nitrogen fixed is estimated based on harvesting the legumes before they produce a significant amount of seed. Once the crop flowers and begins to set its seed, the nitrogen fixed in the soil is picked up by the plant to be used for seed production, and this means that the nitrogen is used up by the time one approaches the next winter season.

An alternative to this sequential rotation of legumes and grains in place is to interplant the legumes with grain. In the late autumn/ winter/early spring season, interplant with winter/spring grains (such as Wheat, Hull-less Barley, Hull-less Oats, Cereal Rye, and Triticale); in the late spring/summer/early autumn season, interplant with summer grains (such as Flour/Tortilla Corn, Sorghum, Pearl Millet, 45-Day Japanese Millet, Grain Amaranth and Quinoa).

For example, to use this inter-planting approach in the late autumn/winter/early spring season, you can prepare, fertilize and apply compost to the growing area and soak 5.5 ounces of vetch seed/100 sq. ft. in room temperature water overnight to encourage better germination. The next day, drain the vetch seeds and mix them with a small amount of dry soil; this will allow the seed to be broadcast more easily. Scatter the vetch seeds evenly over the bed, and using a bow rake, very gently chop the seed shallowly into the soil. Then, using a transplanting board, transplant the winter/spring grain onto 5″ offset centers. When the vetch reaches 50% flower (it looks like full flower)—and before it begins to make a significant amount of seed—carefully remove it from the growing area, cutting the plants at ground level and leaving the roots, with their nitrogen-rich nodules, in place. Then, let the grain continue growing to maturity.

To use the inter-planting method for summer crops, prepare, fertilize and apply compost to the growing area and soak, prepare, broadcast and incorporate 5.5 ounces of vetch seed into 100 sq. ft. of growing bed, as described above in winter crop method. Then, using a transplanting board, plant summer grains such as flour/tortilla corn, amaranth or quinoa on 12″ offset centers in late spring/summer/early autumn. Then, (exactly as described previously in the winter crop method) when the vetch reaches 50% flower, but has not produced seeds, cut the plants at ground level, leaving the nitrogen-producing roots, and allow the grain to continue growing to maturity. For other summer grains such as sorghum, pearl millet and 45-day Japanese millet, which must all be transplanted on 7″ offset centers, follow the same method, but instead of planting the grain on 12” centers, plant the grain seedlings on 7” centers and proceed as above.

The reason for using vetch in the inter-planting examples above is that vetch produces are smaller plants than fava beans and makes more efficient use of the space when sharing a bed with grains. While favas could be used in an inter-planting design, because they are large plants and require wider spacing, when interplanted, they would fix much less nitrogen (1/7th the amount as compared to the amount they fix when planted by themselves) as compared with smaller legumes.

Note: For the best plant health and yield results, there needs to be about 0.5 lbs. of nitrogen in your soil/100 sq.ft.  As you can see from the above inter-planted examples, approximately 0.25 pounds, and sometimes more, can come from the inter-planted legumes. Up to 0.25 pounds of additional nitrogen may be added by applying 2 cubic feet of cured GROW BIOINTENSIVE compost (including ~50% soil) per 100 sq ft. of growing bed.

If you’re interested in learning more about cover crops, nitrogen fixation and crop rotations, the USDA Sustainable Agriculture Research and Education Program (SARE) has an excellent free publication Managing Cover Crops Profitably which you can download from https://www.sare.org/Learning-Center/Books/Managing-Cover-Crops-Profitably-3rd-Edition

A little bit of effort with cover crops now can mean better yields and richer soil in the spring!