September has just arrived. Even though it is not quite fall I can feel the pull of the autumn moon and the precious relief of cool dewy mornings. A welcome reprieve after a hot, dry summer here in Southern Oregon. Sometimes by the time fall comes around I am tired from months of planting, weeding and harvesting. Alas, there are some necessary tasks to complete in order to finish the cycle of helping plants grow.  There is garlic to plant, winter squash to harvest and cover crops to sow. 

For me, gardening is not just about eating amazing food and gazing around at gorgeous flowers. It is about cultivating a relationship between myself and other creatures, recognizing interconnectedness and practicing presence with the world around me. Cover crops are one of the gardening practices that helps me do those things. 

A cover crop, sometimes known as a green manure is a plant that is grown specifically for regenerating soil in between cash crops. Their primary use is to cover the bare soil after crops are harvested. However, there are many other reasons to bring cover crops into your farming or gardening regimen.  Cover crops are like tucking the earth into bed. They help protect the soil from wind and rain erosion, improve soil structure and quality and enhance nutrient availability.  They also help provide dense forage for pollinators. 

There is a large array of research supporting the efficacy of cover crops that explore their various functions in sustainable agriculture systems. One really encouraging use of cover crops is their ability to help agriculture systems adapt to climate change. Cover crops create a large amount of above ground and below ground biomass which helps sequester carbon from the atmosphere. They also reduce the need for fertilizer inputs. Though not a cure all for climate change they may be beneficial in helping us through the future. 

Clovers and legumes are examples of cover crops that form symbiotic relationships with Rhizobium bacteria in the soil. This relationship helps fix nitrogen into the soil. Nitrogen is an important element that is essential to chlorophyll production which is how plants absorb light for photosynthesis.  Fava beans, peas, chickpeas, and clovers are a few excellent choices for nitrogen fixation.  There is research that shows Fava beans grown as a cover crop preceding kale crops specifically increased proteins, minerals and prebiotic carbohydrates. Favas are a great choice because you can also eat the fava beans that they produce.

Cover crops can be planted throughout the year, generally in the spring, summer and fall.  The planting date for your cover crop will depend on the function you want it to have in your garden. During the growing season certain species of cover crops can be interplanted with cash crops in order to suppress weeds and support the growth of your crop. If your goal is weed suppression you want to sow a cover crop that grows quickly.  Buckwheat, sorghum and oats are some examples of plants whose rapid growth effectively suppresses the establishment of weeds.  Cover crops can outcompete weeds for light, water and nutrients.

The most common cover crop planting time in temperate zones is early fall. This allows the winter hardy cover crops to get established before hard frosts arrive. Fall planted cover crops grow rapidly once the days become longer and warmer in the spring. The cover crop can then be tilled into the soil. It can also be crimped, mowed with a flail mower or weed whacked.  You can then plant directly into the downed plant material using it as a lovely green mulch for your new plants.

Incorporating cover crops into the soil leads to an increase in soil organic matter. This helps support necessary parts of the soil ecosystem. Providing food for earthworms as well as many other necessary soil microbiota. 

Most cover crop species come from a few main plant families.  Generally annual species from the Brassicaeae family, Fabaceae (pea family) and Poaceae (grass family) are found most often in cover crop mixes.  These annuals are then terminated before they set seed. Some mustard varieties have the ability to help deal with pests in the soil like root feeding nematodes. Fava beans and forage radish varieties can help penetrate compacted soil with deep tap roots. Perennial cover crops are more common for orchards, vineyards and in garden pathways.

As you can see there are a lot of variables to consider when choosing cover crops.  Cover crop mixes with multiple different species are a good choice in order to get the widest variety of benefits. Choosing a mix can also help mitigate some of the risks of cover crop use which include competition for other soil nutrients besides nitrogen and available groundwater.  A diverse cover crop just like a diverse garden will help attract beneficial insects  and pollinators as well. 

If you are looking for a way to help your garden be more and also deal with common issues that bare soil creates like erosion cover crops will be a great choice for you. I like to cover any beds that would otherwise be fallow. Happy planting!

• To plant cover crops, prepare your garden bed. You can use your preferred method for soil preparation. Some examples are tilling, cutting down or removing crops by hand.
• Evenly disperse the cover crop seed onto the soil. You can use a cover crop broadcaster or do this by hand. I like to walk at a steady quick rate to ensure even dispersal. 
• Lightly rake the soil over the cover crop seed. There are also mechanical ways to spread cover crop seed if you are farming on a larger scale. In Southern Oregon we usually sow or seed in the middle to end of September. Early fall rains help the seed germinate and to get established before the winter. 

Happy Planting!

Taryn Hunter
Lead Seed Coordinator, Siskiyou Seeds

References

Casey J Bryan and others, Efficacy of Cover Crops for Pollinator Habitat Provision and Weed Suppression, Environmental Entomology, Volume 50, Issue 1, February 2021, Pages 208–221, https://doi.org/10.1093/ee/nvaa159

Chapagain T, Lee EA, Raizada MN. The Potential of Multi-Species Mixtures to Diversify Cover Crop Benefits. Sustainability. 2020; 12(5):2058. https://doi.org/10.3390/su12052058 

Kaye, J.P., Quemada, M. Using cover crops to mitigate and adapt to climate change. A review. Agron. Sustain. Dev. 37, 4 (2017). https://doi.org/10.1007/s13593-016-0410-x

Langdale, G.W., Blevins, R.L., Karlen, D., Thomas, D.K., Tyler, D.D. and Williams, J.R. (1991) Cover Crop Effects on Soil Erosion by Wind and Water. In: Hargrove, W.L., Ed., Cover Crops for Clean Water, SWCS, Ankeny, 15-21.

McKenzie-Gopsill, A., Mills, A., MacDonald, A., & Wyand, S. (2022). The importance of species selection in cover crop mixture design. Weed Science, 70(4), 436-447. doi:10.1017/wsc.2022.28

Do cover crops benefit soil microbiome? A meta-analysis of current research,

Soil Biology and Biochemistry,Volume 142,2020,107701,ISSN 0038-0717,

Scavo, A., Fontanazza, S., Restuccia, A. et al. The role of cover crops in improving soil fertility and plant nutritional status in temperate climates. A review. Agron. Sustain. Dev. 42, 93 (2022). https://doi.org/10.1007/s13593-022-00825-0

State University. Extension Service, Oregon, et al. Fava Bean (vicia Faba L.).: Corvallis, Or.: Extension Service, Oregon State University, 1998.

Written by Taryn Hunter