(By Ashley Chesser, Executive Director)
Though I dabbled with growing flowers and veggies in a community garden plot in college, I didn’t start gardening in earnest until about eight years ago when I moved into a house with a yard. In the first several years, I added raised beds and planted a mixture of vegetables, berries, flowers, and ornamental plants. I brought in healthy, organic soil and had successful growing seasons with plump veggies and vibrant blooms. But by the third year, many plants weren’t looking so happy.
Vegetables were smaller and my flowering ornamentals weren’t flowering as much. Something was wrong. The culprit, looking back, is pretty obvious: soil health. Plants were using up the nutrients in the soil and I wasn’t doing any replenishing. One solution to this is to apply organic compost and fertilizers in the spring. And while that is always helpful, I decided to try an additional method for improving soil health that is inexpensive and also great for suppressing early spring weeds. Cover crops!
Cover crops are grains, grasses, or legumes that will grow during fall and winter and that you can cut or till under in the spring to build better soil for gardening. During their growth, cover crops help break up compacted soil and prevent erosion. Their roots penetrate and help loosen heavy clumps of soils, allowing air and water to more easily move through your garden. Legume cover crops (clover, peas, etc.) add nitrogen to the soil. When you turn cover crops under, they add organic matter to the soil—building better soil structure and fertility.
Cover crops are also considered “catch crops.” In the rainy part of Oregon where I live, this might be one of the more economical reasons for planting a cover crop. Grasses and legumes catch and use the nitrogen and other mineral nutrients that winter rains normally leach away.1
September to mid-October is the ideal time to plant cover crops in garden beds. So let’s get started!
[Image description: A lady beetle on a vetch leaf / vetch starting to flower / chard transplant surrounded by a mulch of vetch and decomposing fall leaves. All images are from one cover crop season in my garden, including the image at the top.]
Step 1: Choose a Cover Crop
Deciding what vegetables you want to plant in the spring can help you choose a cover crop. If you intend to plant early vegetables in March, plant a grass cover crop, such as the cereals rye, oat, or wheat, the preceding fall. These cover crops can provide sufficient soil cover for the winter and significant growth before they need to be terminated to make room for vegetable planting. If you are going to plant vegetable crops in April or early May, a legume winter cover crop like crimson clover or vetch will have enough time to grow and provide a nitrogen benefit. Legumes will provide even more nitrogen if the vegetable crop is not planted until late May or June.2 You can also mix cover crops together, which is especially helpful if you have a little bit of a few different seeds on hand.
Step 2: Prepare the Garden Bed
Remove any annual plant remains or weeds that are in the garden plot or bed. Since your garden has been busy producing all summer, it’s good to add some nutrients to the soil before planting to ensure the cover crops will thrive. Use compost or another type of organic fertilizer.
Step 3: Plant the Seeds
Plant your cover crop early enough to permit 4 weeks of growth before cold weather stops that growth. After preparing the soil, you can plant large-seeded cover crops (peas, vetch and wheat) in shallow, closely spaced furrows. Broadcast small-seeded crops (ryegrass, buckwheat) over the surface and cover with a light raking. If the soil is dry, water until the rainy season sets in to ensure the seeds germinate. For the rest of winter, you can sit back and relax!
Step 4: Finishing the Cover Crop
In the spring, about three weeks before you plant spring crops, turn the cover crop under and allow the organic matter to decompose. If the cover crop is too tall to turn under easily, cut it first. If you will be transplanting vegetable seedlings or planting vegetable crops with large seeds, such as beans or corn, you can cut and leave some mowed cover crop on the surface as mulch, rather than mixing it all into the soil. Don’t allow cover crops to go to seed, to prevent them from competing with your food crop. However, if you have enough space, you can set aside an area of your garden for flowering cover crops and keep them around to provide food for pollinators. Crimson clover is an especially good food source for bees. Just be prepared to pull it from areas where you don’t want it growing as it may spread.
- Rackham RL, McNeilan R. Cover crops for home gardens [Internet]. Corvallis (OR): Oregon State University; 1999 Feb. Available from https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/fs304.pdf
- Benedict C, Cogger C, Andrews N. Methods for successful cover crop management in your home garden [Internet]. Washington State University; 2014. Available from http://pubs.cahnrs.wsu.edu/publications/wp-content/uploads/sites/2/publications/FS119E.pdf