Agriculture Reference
In-Depth Information
Grasses
Non-legumes used for cover cropping are often grasses. They're used when your main
goals are creating a lot of organic matter, controlling weeds, and taking up nutrients — es-
pecially nitrogen — from the soil so that they don't leach. If you have a bed that was
mostly planted with legumes such as peas and beans during the growing season, or even
better, if you have a soil test showing a lot of nitrogen in the soil after harvest, it will prob-
ably be more beneficial to plant a grass cover crop. This grass will do a better job than a
legume of keeping a lot of that nitrogen rather than allowing it to leach, and also acts as an
excellent weed control and huge organic matter builder.
While legumes do help build humus, grasses and other grains really excel at this job. It's
partly because they grow fast and get big, but also because they're composed of more cel-
lulose and lignin, materials that contribute to humus. In contrast, an annual clover will
break down more readily and become a much better short-term source of nitrogen and other
nutrients for crops.
Grasses have a higher carbon to nitrogen ratio than legumes, so they break down more
slowly, acting as a longer-term mulch, but this also means the microbes may need to steal
nitrogen from the soil in order to break them down. The implication of that is you don't
want to use too much grass in a garden that is nitrogen-deprived, or at least you want to
turn it in earlier in spring, because the carbon content increases as the plant grows. The
longer breakdown period of grasses also means the nutrients will not be as immediately
available to the next crop.
Winter annual grasses are seeded in late summer or autumn. They grow before winter, go
dormant during winter, and grow again in the spring before we usually cut them down.
Summer annual grasses are occasionally grown during the summer if you've harvested
everything out of a garden bed and aren't going to plant it again until fall.
