Green Manures and Cover Crops in the Vegetable Garden

Both green manures and cover crops perform many of the same functions that traditional composting does. Both crops are eventually turned under the soil and as they deteriorate, they create organic matter. Some of them bring excellent nitrogen into the earth. There are several ways that gardeners can take advantage of green manure and cover crops.

Gardeners plant a “green manure” crop into a garden bed while the main vegetable crops are on hiatus. This is usually done at the end of the growing season. Green manures are a specific plant variety that’s sown into garden beds and then turned under while they’re still green. Green manures add nutrients (predominately nitrogen) back into the soil that the previous food crop has used up; increasing the soil’s fertility for the next season’s vegetables.

Green manures are widely used to rejuvenate soil that’s been over-planted or has had crops that are heavy feeders such as corn. Once your summer crops are harvested, you can literally plant nutritional goods back into the garden bed and improve the soil. When you plant green manures in the fall, they act as a cover crop and keep your soil in the bed where you want it. They also smother and crowd out early spring weeds.

The primary intention behind planting “cover crops” is for soil erosion control and to block weed growth. However, cover crops can perform double-duty by improving the soil’s organic matter, as well.

Both cover crops and green manures are typically grown in areas where food crops are planted. This is because you wouldn’t normally risk disturbing perennial roots or flower gardens by turning another crop under where there are permanent plants. That said, many fruit tree growers use green manures like clover or vetch planted between their rows of trees to encourage beneficial predatory insects. Cover crops are also routinely used along with grape vines.

Protect and Add to Soil Structure

Cover crops and green manures can help soil structure by loosening the earth in heavy, clay soils as down at the root zone. They also reduce erosion by hanging fast to the soil during winter rains. Some of them also “fix” the nitrogen in the soil, as well. After they’ve been tilled under the soil, these plants add organic matter just like compost.

Deep-rooted green manures such as alfalfa will draw nitrogen into the deeper part of the soil. Legumes in general collect nitrogen from the air and store it in their roots which is released once the legume crop dies (or is cut). All cover crops once they’re turned over add organic matter to the soil.

Any cover crop you plant is going to help crowd out or smother weeds that try to invade their space which is a time and back-saver for the gardener. But some of these crops perform this feat admirably. Buckwheat and rapeseed are good examples of cover crops that perform stellar weed control.

Living Mulches

Both green manure and cover crops fall under a loose term called “living mulches”. Groundcover-type plants that are planted in the landscape to cover bare soil are also often referred to as living mulch.

For more articles on soil amendments check out Cover Crop and Green Manure Varieties, What Compost Does for the Vegetable Garden, Trench Composting in the Vegetable Garden, and How Worms Improve Soil in the Vegetable Garden.