I have it on good authority that a cover crop or green manure is a plant that is grown in the garden and then turned over into the soil. It is often a legume from the bean family such as garden peas, snap beans, and butter beans. These plants are known as "nitrogen-fixing" plants. To me, in a most simple term, it means that these plants restore nitrogen to the soil. I am not sure that I would be patient enough to hear a biologist's explanation for this term, nor fully understand it. There is, however, plenty of information on this subject on the Internet.
The UF IFAS Extension scientists, the ones with "Solution for Your Life," begin their explanation of nitrogen-fixing plants by stating that "Much of the topsoil in Florida is very sandy and has very little organic matter." Tell me something that I don't already know. This soil condition is one important reason for adding green manure to the garden.
This is the time of the year when vegetable production is coming to a close for summer here on the Back Forty in Northern Florida. It is getting too hot for the vegetables to grow and too hot for me to plant them and harvest them.
I have just turned over all of the greenery after harvesting the last of the snap beans. The remnants of the bean plants will decompose in the soil adding organic matter, biomass, and providing nitrogen-fixing elements.
For the last few years, we have planted various kinds of field peas in the garden plots. This year, we are planting black crowder beans. In addition to providing the nitrogen-fixing properties and providing us with wholesome food, the black bean plants will control topsoil erosion, reduce weed, pests, and disease.
This is the first time we have planted black beans and it will be interesting to see the result. I spaded the dirt, smoothed it out with a garden rake, and made a furrow a few inches deep and sowed the seeds about 2 - 3 inches apart. It will take 63 days for the beans to mature according to information above the bean bin at the seed store.
Letting the cover crop do its work should give us plenty of time to enjoy the summer before we start gardening in the fall again.
Source: University of Florida Institute of Food and Agricultural Sciences