Marin Master Gardeners
University of California
Marin Master Gardeners

Cover crops boost soil in vegetable beds

Now's the time to enrich your vegetable beds with cover crops


Planting a cover crop is a powerful way to keep soil fertile and healthy. Often referred to as “green manure,” cover crops are fast-growing plants that are grown from seed during the fallow times in the vegetable garden, often in fall and winter. The idea is simple: grow your own organic material right where you need it. The process is also simple: after clearing the garden of a harvested crop, the seeds are sown, the rainy season hastens their growth, and then they are turned right back into the soil before it’s time to plant the next batch of edible crops.  

Legumes and grasses are the two types of cover crops. Legumes are particularly valuable for Marin gardeners because they add nitrogen to the soil. Examples of legumes include fava beans, soy beans, crimson clover, red cover and hairy vetch. Grasses include barley, rye and wheat. Grasses add organic matter, loosen soil and prevent erosion.

The best time to turn under your cover crops is when they are flowering. Be sure to turn your cover crops under before they set seed so that you don’t have any surprises popping up later. Also, you should wait until everything is adequately decomposed before planting your spring crops. The timing on this will depend on how finely you chopped up your cover crops: the bulkier the materials, the longer it will take for complete decomposition.  

In a nutshell, the benefits of using cover crops are:

Soil conditioning, erosion control and nutrient enrichment:  Decomposed cover crop materials provide nutrients directly into the soil, thereby increasing biological activity, water infiltration and soil tilth. Some green manures have roots that can reach down much deeper than any shovel or rototiller, so in essence they’re doing much of your dirty work. Taller cover crops can be weed whacked or mowed, lower varieties can be turned right under. An added benefit is that there is no chance of nutrients being washed away since all of the action is happening underground. Microbial activity is maximized and ultimately supplies food for the earthworms that are critical to soil health.

Weed suppression:  While your soil is enjoying the benefits of cover cropping, your back will be happy to know that many weeds are being smothered or eliminated.  

Inexpensive and easy:  No special tools are required and a bag of seeds is inexpensive. Peaceful Valley Farm Supply (www.groworganic.com) is a good source, as are local nurseries.


Contributor: Marie Narlock

Fava beans grown as cover crop in vineyard.  Photo credit: Chuck A. Ingels, UCCE Sacramento.
Fava beans grown as cover crop in vineyard. Photo credit: Chuck A. Ingels, UCCE Sacramento.
Barley grown as cover crop in vineyard.  Photo credit: Chuck A. Ingels, UCCE Sacramento.
Barley grown as cover crop in vineyard. Photo credit: Chuck A. Ingels, UCCE Sacramento.
This winter cover crop of yellow mustard minimizes weed growth. Cover crops also help conserve beneficial insects by providing them shelter and food.
This winter cover crop of yellow mustard minimizes weed growth. Cover crops also help conserve beneficial insects by providing them shelter and food.
Photo credit: Jack Kelly Clark, Photomacrography, electronic darkroom and pre-press

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