Cover Crops

A cover crop is simply a dense planting of quick-growing plants that protect the soil and can provide many nutrients to the soil.  The most common cover crops are grasses/grains such as Winter Rye.  The other favorites are legumes such as clover, vetch, and peas that fix nitrogen in the soil. When the green cover crop plants are tilled into the soil it is called a “Green Manure” crop.  These terms are used alternately.  You can plant cover crops; during the growing season to keep weeds at bay, in the fall to overwinter adding nutrients and protecting the soil, or in the spring for areas where you will be planting later crops.

Why plant cover crops?

They hold the soil in place.  Providing protection from wind and water erosion.  The dense planting provides weed suppression.  Winter Rye actually has allelopathic properties that inhibit other plant growth.   Cover crops enrich the soil by nitrogen fixation from legume plant species and add organic material for helping the soil structure and providing food for beneficial microbes and worms.  Cover crops help to reduce garden insect pests by attracting beneficial insects and bees and bumblebees are attracted to the early blooms of some of the species.

Soil Protection:

Protecting the soil is very important.  Planting a cover crop is like a living mulch.  The roots hold the soil in place and penetrate deeply into the earth, bringing moisture, nutrients, and airway down into the depths.  The leaves shade the top of the soil keeping the top from desiccation from wind and sun, and allowing the microbes and earthworms to continue to enrich the soil.  Allowing annual cover crop species to just die in place and cover the soil aids in this process and during the winter helps to hold the snow on the soil.  It is important to mulch to cover the soil even if you are not using a cover crop.  Just use leaves, newspaper, or cardboard covered with burlap or netting to hold it down.  The worms love decaying leaves!

Weed suppression:

Cover crops help to combat weeds firstly by sheer numbers.  Cover crops need to be planted thickly.  Weeds love bare soil!  Planting a cover crop in the fall to till under in the spring is a good way to get ahead of the spring weeds.  Try to get a fall-planted cover crop for spring tilling in at least 1 month before killing frosts in the fall.  Use a spring-planted cover crop to combat weeds in areas between rows of crops or in orchards.  Cover crops are effective whether you till or not.  They can just be mowed off and in cold winter areas, most annual cover crops die on their own and are a good mulch in place even when dead.

Soil enrichment:

Clovers and legumes enrich the soil by taking up atmospheric nitrogen in nodules in their roots.  They are able to achieve this because they are a host to a bacterium, Rhizobium. The relationship between these plants and Rhizobium is symbiotic, meaning they are mutual beneficiaries.  The bacteria are fed by the plant and the plant is fed by the bacteria.  Plants cannot use nitrogen the way it exists in the atmosphere.  Rhizobium converts atmospheric nitrogen into a useful form for plants and animals to utilize.  Rhizobium takes up residence in the plant’s root system and forms nodules.  Clover and other legumes are susceptible to this type of bacterial “infection” and that is why these plants are great fertilizing plants.!

Want to know more?

Colorado State University – CMG Garden Notes #244