A Cover Crop for the Edible Garden

It is really surprising to me how many gardeners lose interest in their edible gardens at the end of summer. When I joined the Benicia Community Gardens, Inc.  early last spring, I noticed that most of the beds at the Swenson Garden on the corner of Military and East Second, behind the , had been let go for the winter.  Many of the beds contained dead and dying vegetable plants waiting for their gardeners to come back for spring clean-up.

Not the case at the Benicia Community Gardens located at the corner of First and D Streets. The raised beds had been built during the winter. Each bed had new soil and was planted with a cover crop mix. The crop took off slowly but picked up steam as the weather warmed in the spring and became a thick dark-green blanket over each bed. When the gardeners who signed up for the beds took over in the spring, their first task was to cut down the cover crop and ready the soil for planting. The gardens were spectacular during the summer. If you drove downtown you may have noticed the enormous Tomato, squash and various other plants in most of the beds. The new soil and the cover crop were the reason. Of course the location, which provides a full day of sun, didn’t hurt.

Cover crops, also called green manure, are made up of either a single plant variety such as fava beans, or a mix of plants such as hairy vetch, oats, rye grain, buckwheat, bell beans, peas and clover. They are grown during the winter months and rototilled under in the spring. They improve the tilth (the structure of the soil, the ideal being crumbly particles which hold together when compressed) and nutrient content of the soil. Cover crops can keep the weeds down by crowding and shading them out. They can prevent erosion, improve water and oxygen penetration, attract beneficial insects, and even add needed nitrogen to the soil.

I first started planting cover crops years ago when we lived on a dairy in Graham, Washington, it was too cold to grow winter vegetables so, in the fall I planted cover crops of rye grain otherwise known as cereal rye. Annual rye grass is also used as green manure but I was careful NOT to plant perennial ryegrass as I didn’t want a lawn in my vegetable patch!

In the Spring I tilled the rye grain under when it reached about knee high. Some years I let it grow too tall and when I tilled it under the plants wound around the rototiller tines, forcing me to stop often and cut it out with a knife.

What I like about rye grain is the plants are thin and when rototilled into the soil, break down quickly… plus its roots are long and fibrous reaching deeper into the soil than my rototiller, helping to loosen the soil and allow oxygen and water to penetrate deeply. Rye doesn’t release nitrogen into the soil as legumes do such as vetch, clover, and peas but I had more than enough nitrogen with the manure from the dairy cows.

I have not used cover crops for years, but last October I decided to plant one in my 20 by 20 foot garden plot in Fairfield because for two years I had fought with clumpy clay soil which was nearly impossible to work up more than about four inches deep. After cleaning out the area of all the spent summer vegetables plants, I loosened the soil with a rake and broadcast a mix of vetch, clover, rye grain and fava beans. I then raked it in, threw extra soil on the top, and watered it. The recommended depth for the seeds is between ½ to 1½ inches so I didn’t need to be exact. I only had to water a couple times before the winter rains set in and I didn’t do anything else but watch it grow. The area became a three foot high thick mat of beautiful, dark green shiny plants.

In the spring, when flowers started appearing on the fava beans, I knew it was time to cut it all down as I didn’t want any part of the crop going to seed. If it goes to seed, babies from the cover crop will come up during the summer and compete with the edible plants not to mention resulting in more weeding time for me.

The mass was so thick and tall I knew I didn’t want  to till it under (cleaning rototiller tines is not my favorite task) so I cut it into foot long lengths with a hand held hedge trimmer and piled it in a row down the middle of the garden. I let it dry and used it as mulch later in the summer. I left the roots in the soil to rot for about two weeks before rototilling the garden to prepare the soil for summer planting. If I had rototilled the green tops under along with the roots I would have let it sit for six weeks to give it time to break down before planting my summer garden. When I worked up the soil, the clay clods broke down easily and I had the best seedbed since I started the garden three years ago.

If you are not planning to grow winter vegetables or have heavy clay soil, the best thing you can do for your garden is to grow a cover crop. You can find the seeds locally at Mid City Nursery. They carry fava beans, clover, buckwheat, vetch and others in separate containers and have knowledgeable staff to help you. There are lots of web sites with information on cover crops, but the UC Agricultural & Natural Resources site seemed most helpful. 

Winter’s coming!  Put your garden to bed with a cover crop.