This post was contributed by Scott Behmer, Seattle Community Farm Coordinator.
Unlike veggies that we grow to feed us, we grow cover crops to feed the soil. They do many wonderful things like preventing erosion and water runoff, providing nutrients to the soil, and suppressing weeds.
When planting cover crop for winter, September is ideal and October is okay. The basics are similar for planting in either summer or winter. For winter, plant the cover crop in September. It will grow throughout the winter, competing with the weeds that would otherwise grow, holding the soil in place to prevent erosion and some runoff, as well as soak up lots of water to prevent more runoff.
When spring rolls around, till (mix) the cover crop into the soil where it will decompose and add their nutrients to the soil. It’s like composting, but directly in your garden bed. For nutrients, the ideal time to till cover crop in is as soon as it starts to flower. After that, the plants will instead be putting their nutrients into their seeds where they are less available to the soil, and if you wait until the seeds are produced it may become a weed itself.
You should allow two or three weeks for the cover crop to decompose before planting. If you run out of time before planting there are two options. You can either till in the cover crop early, or yank it out and compost it in your compost pile instead. If planting cover crop for the summer, the process is the same except it will grow much more quickly.
There are many different plants that are well suited to be a cover crop and many times of the year that you can plant them. They are most widely used over the winter when many veggies aren’t growing anyway, but you can also plant them in summer if you have a space that won’t be used for a while.
One of the most popular summer varieties is buckwheat. Buckwheat is fast growing and produces a lot of plant matter quickly. Over-the-winter popular varieties include field peas, vetch, clover, fava beans, and cereal rye (not perennial rye). It’s also very common to mix a few varieties together.
Cover crop photos by Steve Tracey