- Author: Help Desk Team
What is a cover crop? It's a crop grown to feed and protect the soil when the garden is not being used for active food production. Cover crops can transfer nitrogen into the soil, provide large amounts of organic matter, act as a mulch to prevent erosion, improve soil structure, promote water infiltration and retention, suppress weeds, and stimulate beneficial microbial soil life. That's impressive for a small packet of seeds. And they can be beautiful and attract beneficial insects and pollinators.
What kinds of plants can be used for cover crops and what roles do they play?
- Legumes have unique relationships with soil bacteria, allowing the plant to transfer, or fix, nitrogen from the air into the soil. In addition, they produce hefty biomass (green, leafy material). This can be cut down and used as mulch, it can be turned into the soil to act as a green manure (decomposing in place), or it can be used as a compost crop and added to the compost pile as a nitrogen source.
- Grains and grasses have a different relationship with the soil because of their deep root systems. The action of the roots loosens and aerates the soil, providing channels for air circulation and water flow. Grain plants tend to be tall which results in an abundance of biomass for mulch, green manure, or material for compost.
- Broadleaf plants are used as cover crops for their rapid growth and big leaves. They establish quickly, shade out weeds, prevent erosion from water and/or wind, and generate heaps of biomass for mulch, green manure, or compost material.
- Check this link to see the UC ANR Cover Crop Database where you can find information on a variety of cover crop plants: https://sarep.ucdavis.edu/covercrop
Purchase cover crop seed from a local nursery or from an on-line seed company. If you decide to grow a legume cover crop, it is recommended that you buy “inoculant” powder at the same time you purchase your seeds. The inoculant is a natural bacterium that helps the legumes with the nitrogen conversion. When you're ready to plant (September or October is good), put some inoculant powder on a plate. Wet the seeds and roll them around in the powder.
Evenly broadcast seeds over the area you want to cover. You can make neat rows, or you can spread the seeds over the entire area. Cover the seeds with soil from ½ inch to 1½ inches deep depending on the size of the seeds. Keep the soil moist for the first week to aid with germination and then water as needed when the soil dries.
To get the maximum amount of nitrogen from a legume crop, cut or mow it after it starts flowering in the spring, allowing several weeks for the mass to decompose before planting something else. For other types of cover crops, cut them before they go to seed, or several weeks before you want to plant your crops.
Is it worth the effort to grow plants you're not going to eat? You bet it is! Deciding to grow a cover crop will be one of the best decisions you make for your soil's health and overall vegetable production. Cover crops will save you time, energy, and money and we can all use more of each of these.
Sources and Resources:
- This link will give you planting instructions and harvesting guidelines: https://marinmg.ucanr.edu/EDIBLES/COVERCROPSETC/
- The following suppliers are good sources for cover crop seeds
- Peaceful Valley Farm and Garden Supply
- Territorial Seed Company
- True Leaf Market (also has an excellent free guide for cover crops that you can download)
Help Desk of University of California Master Gardener Program of Contra Costa County (BHD)
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Client: Is it possible to plant a nitrogen-fixing winter cover crop simultaneously with wildflower seeds…..or will they just compete for space? Thanks for your answer.
MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program with your question about planting a nitrogen-fixing winter cover crop together with wildflower seeds.
There are some alternatives, but they may not be optimum for what you want to achieve. One is to plant the cover crop first and then the wildflower seeds after the cover crop has been dug in. The problem there is that may lead you to digging in the cover crop too early, or more likely, planting the wildflower seeds too late. Wildflowers seeds can be sown in early spring, but October to January is generally the best time to sow wildflower seeds. Otherwise, I am afraid that you will need to decide between planting a cover crop or wildflowers. If you are planning to turn the area into a wildflower garden, and are planting California native wildflowers, you could skip the cover crop since native wildflowers generally do not need a lot of nitrogen. On the other hand, if you are planning on turning the area into a vegetable garden, I would recommend planting the cover crop seeds and perhaps planting the wildflowers in another area of the yard.
Another option you could consider would be getting a cover crop mixture that would provide different flowers. You might find these mixtures at your local nursery as well as on-line.
You can find some basic information from UC on growing cover crops at: http://ucce.ucdavis.edu/files/filelibrary/5842/25997.pdf
Note that this is a bit out-of-date in its comment about cover crop seeds being hard to find; that is no longer true. It also mentions rototilling. You can just cut the plants down and dig them in.
Here is also some information from the California Native Plant Society on planting wildflower seeds: https://www.cnpsmarin.org/native-plants/how-to/item/185-marin-cnps-sowing-wildflower-seeds
I hope that you find this information helpful. Please let us know if you have further questions.
Good luck with your winter garden!
Help Desk of the UC Master Gardener Program of Contra Costa County (ECS)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925)646-6586, email: firstname.lastname@example.org, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/)
Help for Home Gardener from the Help Desk
of the UC Master Gardener Program of Contra Costa
For this posting we cover two activities that hopefully could be of interest to you.
Planting a cover crop is highly recommended, especially for over wintering vegetable gardens. “They protect the soil, feed microbes, build soil structure, add root channels, and support beneficial insects.” That quote comes from a December 21st publication (attached) of Washington State University's Andrew McGuire where he summarizes recent studies which show that single species of cover crops out perform multi-species cover crops. It seems that contrary to the notion that having a “polyculture” (lots of different species) of seed for your cover crop, the use of monoculture (one species) of seed is actually better. Quoting from his paper:
Research thus far has consistently found that cover crop polycultures are not necessarily better than cover crop monocultures. This is now reaffirmed by a large study, done in Pennsylvania, published this year (Finney et al. 2016).”
So now you know… your cover crop can just be a single seed for the garden. Read the paper (4 pages) for more ideas on what you should be doing to get a great cover crop.
Good Gardening Videos
If you are hungry for some visual gardening in the middle of some rainy, dreary non-gardening day this winter, we recommend considering a relatively new web site, goodgardeningvideos.org. While many videos show up on YouTube and various other gardening organizations (e.g., Cooperative Extensions), the people behind GoodGardeningVideos, you'll recognize many of them, is curating gardening videos for quality and accuracy. Try it; you'll like it. Just remember we live in California, and some of the areas where the videos come from are already deep in snow… and probably won't be putting out their tomatoes in late April either. Their current interest is seed starting. We can do that. Only about 60 days till tomato seed starting time.
Help Desk of the UC Master Gardener Program of Contra Costa County (SIM)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: email@example.com, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).