Americans are eating more broccoli than ever (consumption has jumped 940 percent since 1971), but it still ranks pretty low among vegetables grown in home gardens. Now, based on their highly successful system for growing tomatoes in a vetch mulch, USDA horticulturists have developed a no-till method for growing fall broccoli in soybean mulch rather than in bare soil. The method produces comparable yields while reducing the reliance on herbicides and chemical fertilizers. The system is a real boon to organic market gardeners and those planting on slopes or in dry areas where mulching is crucial.
Here's the USDA method for zone 7: In early spring, fertilize the planting area as you normally would. In May, plant a forage-type soybean. Actually, you can plant any high-nitrogen legume, such as bush or fava beans, that produces a lot of plant matter (biomass). Plant in rows at standard spacing, or evenly broadcast the seed. In late June or early July, sow broccoli so seedlings are ready to transplant five weeks later. A few days before transplanting, chop or mow down the soybean plants to form a 2- to 3-inch-thick mulch that will inhibit weeds, retain moisture, and enrich the soil. Transplant broccoli seedlings with a good root ball directly into the mulch at standard spacing and without any tilling. Any broccoli variety adapted to your area works fine.
As the legume mulch decomposes, it adds nitrogen and organic matter to the soil. The result is healthy broccoli that requires less water, little weeding, and fewer fertilizers. (Gardeners with sandy soil may need to supplement with nitrogen fertilizer.)
Researcher John Teasdale says this system adapts well to different areas of the country. In the North, sow soybeans or other legumes in April or May, and transplant broccoli by mid-July. In the South, wait until mid-August before setting out broccoli transplants. In the desert Southwest, plan on transplanting broccoli seedlings in October for a winter crop.