By: Erin LaFaive, Horticulture Educator UW- Extension, Eau Claire County
Gardens that are worked year after year lose nutrients and organic matter. Adding materials such as partially rotted barnyard manure, composted cow manure, compost, or green manure crops, assists in correcting this depletion problem.
Green manures are also referred to as cover crops. For the home gardener, some of the more easily managed cover crops include buckwheat, oats, and berseem clover because they can be cut and tilled into the soil with hand tools. The key to successfully using cover crops is to cut them BEFORE they create seeds. A flowering cover crop is a sure sign that you must cut them down ASAP.
Cover crops are also beneficial because they help to smotherweeds by blocking the sun-preventing weed seeds from germinating. Cover crops’ root systems can break up compacted soils, adding air pockets within the soil for much needed space for roots and water to navigate. Organic matter is re-introduced to the soil as roots, and leaves decay after the plant is cut and tilled. Some cover crops attract beneficial insects that prey on plant eating insects.
Types of Cover Crops
Buckwheat is an annual, warm-season plant that grows quickly. It sends out a chemical through its root system to inhibit other seeds around it from sprouting, including quack grass seeds. It attracts bees and other pollinators as well as beneficial insects such as lady bugs and lacewings. If you have a Japanese beetle problem, this is not your cover crop as it has a tendency to attract them.
Oats are a fast-growing, cool-season grass. Planted in late summer, it will produce a large quantity of dry matter. It can survive the first few frosts in the fall. It will be killed by winter and easily tilled into the garden in spring.
Berseem clover is a fast-growing, cool-season annual. It can fix nitrogen from the air through its root system. After tilling the plant into the soil, the nitrogen is released in the soil for plant use. It tolerates a light frost.
When to Seed
When to seed a cover crop varies depending on garden establishment and harvesting schedules. In general, cover crops are planted in early spring or late summer. Here are a few recommendations for specific situations.
New garden beds established in spring or early summer can benefit by growing one or two crops of heat-loving buckwheat or beans. New gardens started in late summer benefit from a cover crop that grows quickly in cool weather, including ryegrass, rapeseed, or oats. The dead plant material is turned into the soil in late fall or the following spring.
Another way to use green manures is in established vegetable gardens after early-maturing vegetables have been harvested. Some gardeners continue to plant vegetables that thrive in hot weather or later in the season for vegetables that thrive on the increasing cool weather of the oncoming fall. For those gardeners that need to help depleted soil or simply don’t want to plant a successive crop, plant green manure where these vegetables were growing to keep garden weed free, prevent soil erosion, and add organic matter to the soil. Turn in the dead plant material after a killing frost in late fall.
How to Plant Cover Crops
Things to Consider
Some cover crops can reach heights of two feet. Ask yourself if you will be able to mow a few times as it grows before incorporating the clippings into the soil. If not, the clippings may become matted down by snow pack, which can lead to slow soil warming and drying in spring.
If something prevents you from cutting the cover crop before it flowers, consider finding someone who can. If not, seeds will be added to the soil, and they’ll be popping up in the vegetable garden again. If they do reseed, consider allowing the cover crop to sprout and cut it when the time is appropriate. That garden may need to rest for a growing season to allow the seed bank to eliminate itself through a successive growing pattern. Through the use of green manures the soil will contain more organic matter and beneficial microoganisms and have fewer weeds than before.
Cover Crops for the Home Garden by John Hendrickson and Jim Stute http://tiny.cc/flknv Erin LaFaive is the horticulture educator for UW-Extension in Eau Claire County. Erin earned a M.S. in Environmental Studies from the Nelson Institute for environmental studies at the University of Madison-Wisconsin. She also earned a B.S. in geography with an emphasis in natural resource management at the University of Wisconsin-Eau Claire.