Why You Should Grow Cover Crops
For the Soil and for Morale
I once heard a flower farmer refer to cover crops as “one of the best things for a farmer/gardener’s mental health” as well as for the garden. She spoke about how discouraging it can be to look at a bare patch of dirt over the winter, and how during the hottest part of the summer (when many crops struggle and the chores are too many) it’s nice to see a patch of buckwheat thriving, not demanding much from you. While I think she is right, this barely scratches the surface when it comes to the incredible things cover crops can do.
Soil issues can seem enigmatic and can be difficult to pinpoint: too much clay, too much sand, not enough drainage, not enough nitrogen… the list goes on. It can feel overwhelming when you are trying to determine why your garden isn’t doing as well as you want it to, or why it isn’t producing like you think it should. In every case though, building up diversity of life in the soil will help tremendously. When trying to build a sustainable gardening or farming practice, no shortcut is worth your time, and in fact, shortcuts often cause more complex issues anyway. Long term solutions take time and patience, but they’re usually worth it if you can wait for the results.
One of the simplest long-term solutions to many soil issues is the use of cover crops. Cover crops are plants whose purpose is to cover the surface area of a space, not necessarily to be harvested as food, and are used as part of crop rotation throughout the seasons. They are sometimes referred to as “green manure” or “living mulch” because of how they feed the soil, improve water retention, and much more. The use of cover crops has been studied quite extensively and they have proven themselves to be extremely beneficial to the soil and subsequent main crops. Some cover crops fix nitrogen for future plants, some work to control weeds, while others attract beneficial insects and pollinators that will help control unwanted pests during the growing season. Some cover crops can tackle more than one of these issues.
Cover crops can be an important part of the soil food web. They help ensure that you have a sustainable resource for contributing nutrients and organic material to your garden. Growing cover crops can help some of the worst soil issues. Just to name a few, they can cover bare soil, eliminate the need for tilling, eliminate the need for synthetic chemicals, prevent erosion, and even eliminate pathogenic bacteria.
What is the Soil Food Web?
The soil food web is the complex system of organic material and organisms that live in, and decompose material within, the soil. The creatures at the base of the soil food web are bacteria and fungi that break down organic material and turn it into bioavailable food for plants. Above these creatures are protozoa and nematodes, who feed on bacteria and fungi, releasing that nitrogen back to the plants. Larger organisms like beetles and earthworms then consume the organic material and break it down further. Larger animals like birds, mammals, and reptiles consume the smaller creatures of the web and contribute to the cycle by leaving waste that becomes microbial food sources which are then recycled into plant nutrients, cycling microbes from their own bodies back into the soil web. Even after their deaths, these animals are consumed back into the web of life and decomposition.
Studied & Proven Benefits of Cover Crops for the Soil Food Web
Cover crops have been scientifically proven to provide major benefits to soil and to main crops by increasing diversity of beneficial fungi in the soil, suppressing unwanted weed growth, increasing nitrogen in the soil, fighting pathogenic, disease-causing bacteria and nematodes, improving soil structure, attracting beneficial insects that help control garden pests, improving drainage, increasing organic material in the soil, and improving water retention in the soil. Yes, really, all of those things! Though it may take a year or so to see the results, growing cover crops is one of the best things you can do to improve your soil and your main crops.
Cover crops tend to be relatively fast-growing and don’t require much from their soil. They are typically grown in between main crops, but you can also grow them right alongside your main crops. It’s easy to scatter seeds, mix them into the dirt, water them, and watch them grow in a matter of days to a week. Having something growing and covering the soil is one beneficial step for your garden. Bare soil is the garden’s enemy, because when left exposed, soil is at risk of being washed away or totally dried out by the elements. The beneficial microorganisms within the soil die due to lack of protection making it no longer soil, but mere dirt. Once the cover crop establishes its roots, they will hold the soil together, improving the overall structural integrity in your garden. This is especially helpful if your garden is on a slope. When heavy rains or wind come, the soil will not be washed or blown away, but will be held steadily in place.
Cover Crops & Rhizobia Bacteria
As roots of the cover crop become more established, they will begin to form a symbiotic relationship with fungi, bacteria, and other microorganisms in the soil. For example, Rhizobia bacteria (which is naturally occurring in soil) converts nitrogen gas into a bioavailable form of food (ammonium) for the plants to consume. The plant then converts sunlight into carbohydrates which they feed to the rhizobia bacteria. This is the process of “fixing” nitrogen into the soil. As a note, you will want to terminate the cover crop before it goes to seed to get the most nitrogen from it.
Cover Crops & Fungi
Mycorrhizal fungi live in the soil, especially around the roots of plants. They break down organic material, releasing nutrients in a bioavailable form for cover crops to consume. The fungi, after being fed carbohydrates from the plant, will go down deeper into the soil than the plant’s roots are able to in order to bring it nutrients.
Other Soil Food Web Relationships
Cover crops in the brassica family put out exudates, or substances secreted by a plant or insect, in the root area which also feeds soil life. Cover crops with a deep taproot, like Daikon radish for example, draw up nutrients to the roots of plants from the deeper subsoil by extending their taproot further than the more shallow roots of other crops while also aerating compacted soil by breaking it up. These examples are just the beginning of the long list of benefits cover crops bring:
Eliminate the need for chemical pesticides and herbicides by decreasing weeds while attracting beneficial insects and microbes
Improve the soil’s ability to retain water, meaning you have to water less often, which conserves water
Increase soil fertility overall
Improve drainage in heavy clay soil
Has been proven to suppress disease in crops such as soil splash and fruit rot by triggering an immune response, protecting the plant
Increase microorganisms in the soil which improves plants’ immune responses
Though their main purpose is not to serve as food, you can harvest and eat most cover crops, with some exceptions (such as Hairy Vetch)
How to Choose Cover Crops
Now that you’re totally convinced to grow cover crops in your garden, which type(s) should you grow? You’ll need to ask yourself a few questions before choosing which cover crops to grow.
1. What does your soil need?
2. Which crops will you grow after the cover crop?
If the soil is lacking nitrogen, legumes are best to fix nitrogen into the soil.
If it’s too compacted and needs to be broken up, cover crops with a deep taproot like Daikon radish can extend themselves deep into the soil, de-compacting it over time.
If attracting pollinators is your priority, choose flowering cover crops such as buckwheat or clover.
If your subsequent crop will be sown directly into the soil, you might opt for a lighter-bodied cover crop like peas or clover to make it easier to access the soil.
If your subsequent crop will be transplanted when it’s larger (like a tomato or pepper), heavier grasses
If you have pathogenic fungus or other nasty stuff, crops in the mustard family can help clean those up.
Here are some great options to consider when choosing which cover crops to grow:
Winter rye: loosens soil, increases mycorrhizal fungi
Winter barley: has large biomass (the amount of plant matter that will feed the soil), very cold hardy
Triticale: great for soil life, excellent root system, very cold hardy
Vetch: fixes nitrogen, good biomass, con: can become a weed if not well-managed
Daikon radish: busts up compacted soil, improves drainage
Crimson clover: fixes nitrogen, attracts beneficial insects
Buckwheat: grows fast, attracts beneficial insects, breaks down quickly
Cow peas: fixes nitrogen
Dwarf sorghum: great biomass, weed suppression
Flax: fast growing, suppresses weeds, beneficial insects love it
Many of us don’t just need our cover crops to do one thing, and that’s okay. You can make a mixture of these and even add in wildflowers or other crops and broadcast them all together. There are no fixed rules, only guidelines and a few questions you need to be able to answer before planting. There are many, many seed companies out there where you can buy reliable seeds for cover crops. We typically purchase ours from Johnny’s Seeds and/or Botanical Interests and have had good germination rates from them.
Cover crops can be planted from midsummer to fall for overwintering and as early as the soil can be worked in the spring, depending on your priorities. You just need to look at the days to maturity of your cover crop to make sure it will be mature enough when you terminate it to plant your main crops. Keeping cover crops in rotation with our main crops throughout the year has helped significantly to improve our soil and our crops.
Terminating Cover Crops Before Planting Your Main Crops
Growing cover crops to cover bare soil is a great first step, but you need to put the mature plant material back into the soil to take full advantage. There are a few options when it comes to how to terminate and incorporate your cover crops back into the soil:
First, you should know that it’s completely fine to plant seeds or transplants for your main crops directly in the ground amongst the cover crops. For example, in the hottest part of this past summer, we planted certain crops within the hairy vetch and oats to provide them with a bit of shade and shelter from the harsh elements.
The second option, and probably the most common thing to do with mature cover crops, is to “chop and drop” them. Cut the plants about ¼” to ½” above the surface of the soil and chop the plant matter up into small pieces. Leaving these on the soil’s surface provides you with mulch which will suppress weeds while also retaining moisture. At the same time, leaving the roots in the soil allows them to slowly decompose, maintaining the soil’s structure and providing a slow release of nutrients to subsequent crops. You can also cover them with a tarp or other material in warm weather for a few weeks until they die off, then proceed to use them as mulch, planting subsequent crops interspersed within the cover crop.
Last, you could choose to till them into the soil to decompose, then add a layer of mulch on top. I do not personally recommend this option, however, because it adds work that I feel is unnecessary and possibly even detrimental to building your soil. A little bit of tillage isn’t the worst thing, especially if it involves adding amendments like cover crop or compost, but it does pose the risk of disrupting the microbial activity in the soil food web. It also destroys the structure that the roots provide.
It’s never too late to start cover cropping. Starting now and successively planting them throughout the year is one of the best ways to start building up soil that’s full of healthy microbial life. Even if this is your garden’s first year, you can grow your cash crops alongside the cover crops if you wish to see how things do right off the bat. The first garden year hardly ever produces a satisfactory crop anyway, so you don’t have anything to lose. Interspersing native wildflowers or annuals like brassicas or leafy greens may even result in a small harvest while building your soil for next year.
Cheers & until next time,
Allyson
