Cover crops are the ultimate garden multi-taskers, helping gardens of all sizes produce more. They improve soil tilth, safeguard nutrients, smother weeds, and control pests. Soil scientist have provided compelling evidence that properly growing cover crops will improve yields in any vegetable garden, orchard, high tunnel or field crop.
Using cover crops is less expensive and more environmentally friendly than using chemical fertilizers. USDA researchers have examined cover crop effectiveness in long term studies such as Eric Brennan’s research in Salinas California. He says: “The greatest improvement in soil health was in the system with compost and a cover crop every winter, which had an increase of soil microbial biomass carbon of 179% over six years”.
How do cover crops make gardens more productive?
improve soil tilth
Cover crops, also known as green manure, decompose quickly when turned into the soil. Rye, rye grass, and sorghum sudan grass are particularly helpful when trying to build up soil tilth. They create a lot of biomass in a short time. The combination of added biomass and cover crop roots helps to loosen compacted soils.
Turning cover crops into the soil also feeds microbial life and strengthens the soil’s microbiome. The microbes in turn help cycle nitrogen and other nutrients into forms accessible for plant roots. Modern agricultural tillage stirs up the soil and creates a microbe frenzy that quickly exhausts the microbiome. Gentle turning of the soil, using a broad fork to aerate, or cut and drop are excellent ways to allow natural processes to slowly incorporate new organic matter.
safeguard nutrients and moisture
Bare soil tends to leach nutrients, whereas cover crops seek out and absorb nutrients. Their roots absorb excess rain water and prevent nutrient runoff from polluting waterways. Cover crop grasses mown and left on the surface smother weeds and keep soils moist.
Cover crops prevent erosion with their roots and also by encouraging soil microbes and fungi which band together to hold soil in place.
Cover crops such as buckwheat and red clover are fast growers. Seeded at a high density, buckwheat will quickly cover the soil and prevent weeds from sprouting. Other cover crops such as oats and subterranean clover are allelopathic, which means that they produce natural chemicals that stall or deter growth of plants around them.
Cover crops provide habitats and food for beneficial insects and helps them remain onsite until they are needed to feast on pests.
Encourages diversity among microorganisms – makes plants more resiliant. Better able to resist diseases and pest.
Types of cover crops
I wish there was a poster version of this amazing USDA Cover Crop chart! It is patterned after the periodic table of elements, but instead is organized by types of cover crops: grasses, legumes, grains, and brassicas. The color groups and symbols in each box help us visualize potential cover crop combinations.
For example, oats (grass/grain) plus berseem clover (legume), may be a good combination as they both contribute different things to the soil, but have similar water requirements and temperature preferences.
Combinations of cover crops
There is no silver bullet among cover crops. They each have their strengths and it’s important to decide what your primary objective is in planting a cover crop. Mixing grasses and nitrogen fixers (legumes) helps prevent nitrogen immobilization and allows each to contribute their benefits.
I’ve found it hard to choose which varieties and which combinations of cover crops I’d like to try in my garden. So I did some digging… research, that is, and created a chart for my fellow Mid-Atlantic gardeners/farmers listing all the crops that SARE’s incredibly informative guide recommends for our area.
Download the full chart here.