Green Manures and Cover Crops: Plants That Give Back

For years farmers have been rotating their crops and planting “Green Manures” or “Cover Crops” in their fallow (unused) fields.  Green Manures are plant varieties which help to replenish nutrients to the soil that your plants have absorbed and used to grow and produce fruits and flowers throughout the season.

These specialized, nutritional plants store or “fix” these nutrients into the soil, or themselves, and then are turned back into the garden early in the spring (using a shovel or tiller). Use of green manures can drastically reduce or even eliminate the need for fertilizers in the spring. But that’s not it! Other positive benefits of cover crops include:

• Weed suppression. As cover crops establish themselves, they out-compete pesky weeds.
• Creating habitat for pollinators and beneficial predatory insects.
• Keeping the soil from becoming compacted or eroding. Wind and water can do enormous damage to unprotected ground in a short amount of time - green manures stabilize soils and protect against erosion.
• Bio-accumulators / Dynamic accumulators. Some varieties have extremely deep roots, which tap into nutrients deep within the soil and bring them to the surface.

The list is extensive, but below are some of the better-known varieties.

The Legume Family is one of the most widely used Green Manures. Consisting of many different types of Clover, Peas, Vetch, and others, legumes contain symbiotic bacteria in their root systems, which help to fix nitrogen into the soil in a form that future plants can use.

You may have heard of using legumes in 'succession planting' - an idea that illustrates green manures in action. Because 'heavy feeder' crops like corn require nitrogen-rich soil to produce great-tasting ears, farmers and gardeners alike must figure out how to replace all of that nitrogen after each crop has been harvested. One simple answer is to plant beans or peas directly after corn - two well-known legumes that are infamous for leaving a slew of nitrogen in their wake. So, peas follow corn, which then gets planted again and is followed by peas (or clover, or beans), which then follow corn all over again - all in succession!

Other common green manures not in the Legume Family, including Rye, with its deep roots and hearty characteristics, great at withstanding colder temperatures and decreasing erosion, as well as buckwheat and sorghum.

1. Plant Early to Mid Fall to prepare for spring planting, or plant in early spring to prepare for Summer or Fall planting.
2. Let your cover crops grow. Some hardier varieties will grow very slowly in colder temperatures, and then resume growth in the early spring. Others will die back after a hard frost (this is called 'winter kill').
3. About 3-6 weeks before your new planting, mow down the cover crop before it goes to seed. Then till in to the soil to add organic matter and additional nutrients to the soil. 
4. Always wait 3-6 weeks after tilling to plant your new crops to allow time for the nutrients to be released into the soil through decomposition.  Also, in the case of cover crops like Rye, the compounds which keep other seeds from germinating (one of its main benefits for weed reduction) will no longer be present to interfere with your new plans.