Plants greedily soak up soil nutrients, leaving the soil weak and malnourished, that is how we tend to view it. But, look at a natural ecosystem. There are plants that mine nutrients from deep down and bring them to the surface, plants that fix nitrogen, pioneer plants that pave the way for others and a long list of other plants that maintain soil health without human intervention.

The home gardener can learn from these natural systems and use plants to build healthy soil.

Plants used to build soil are referred to as cover crops or green manure, and growing them will return nutrients to your soil, prevent soil erosion, retain water, provide nectar for pollinators and suppress weeds.

What Are Cover Crops

A cover crop is a plant/s that is typically planted at the end of the growing season (late fall/early winter). Before these plants mature they are chopped down and mixed back into the soil providing valuable nutrients. Cover crops are divided into legumes and non-legumes.

Legumes

Beans and peas are the most common legumes but this family also includes alfalfa, clover and vetch.

While most plants use soil nitrogen for growth, legumes actually pull nitrogen from the atmosphere and “fix” it in the soil through a partnership they form with bacteria on their roots. This ability to produce their own nitrogen is also why leguminous plants grow so quickly (Jack and the Beanstalk for example).

Inoculating: Legumes fix nitrogen in the soil through a relationship with Rhizobia bacteria. If these bacteria are not present in your soil the plants will not be able to fix nitrogen. Inoculating your seeds before planting helps ensure the bacteria will be present. After you have grown inoculated legumes the bacteria will be present and you will not have to inoculate in subsequent years.

The fava bean roots on the left come from soil where Rhizobia bacteria was not present. The fava beans on the right were grown in soil that did contain Rhizobia bacteria (note the white nodules on the roots indicating the presence of Rhizobia bacteria).

Fava Beans are one of my favorite cover crops because, in addition to nitrogen-fixing, you can eat the young leaves, flowers and if you leave the plant in the ground long enough, beans.

White clover is a useful low growing cover crop to sow in the rows between your main crops. The clover will act as a living mulch suppressing weeds and holding in moisture. You will need to mow it to keep it short. The decaying clover left on the ground will return nitrogen to the soil.

Purchase White Clover Seed

White clover, Trifolium repens, is a good choice for living mulches. It adds nitrogen to the soil, is low growing and tolerates some foot traffic.

Non-Legumes

Non-legume cover crops include grasses (wheat, rye, barley, oats) as well as brassicas. The grasses typically grow quickly and have extensive root systems that scavenge for soil nutrients. The plants bring these nutrients to the soil surface and release them back into the soil after they have been chopped down. Tilling grasses into the soil adds large amounts of organic matter. 

Brassica cover crop develops a deep taproot (up to four feet) that can help penetrate and break up compacted soils.

How to Choose the Right Cover Crop for You

You can use the guidelines above to choose a cover crop for your specific situation but if you are looking for general soil improvement go with a cover crop blend. Contact your preferred seed company to discuss which cover crop might be best for your specific climate and soil type. Peaceful Valley carries a wide selection of cover crops. 

How To Plant Cover Crops

Plant cover crop one month before your first fall frost. Some cover crops, such as rye and white clover, can be sown up until the first frost.

Loosen your soil to a depth of 3 inches and remove any vegetation.

Broadcast cover crop seed by hand onto your prepared soil. Application rates vary so consult the seed pack for direction.

Gently rake the seed into the soil to protect it from birds.

Keep the cover crop moist until it germinates. Cover crop is very low maintenance and can mostly be neglected other than an occasional watering if there is little rainfall.

Gently rake the cover crop into your soil.

Returning the Cover Crop to the Earth

The cover crop will go dormant during the winter then grow rapidly when spring arrives. About three weeks before planting your spring crops cut the cover crop to the ground. Depending on the crop you can mow it, use a string trimmer or scythe. I prefer to use my hori-hori (my favorite garden tool) but this may be impractical for large areas of cover crop.

I like using a hori-hori to chop up cover crop.

After the cover crop is mowed or chopped into tiny pieces mix it into the top layer of soil.

Allow the cover crop to decompose for two to three weeks before planting your spring crops.

Nature hates bare ground. By cover cropping, you keep your soil covered year round. Your cover crop works for you suppressing weeds, building soil, retaining water, providing habitat, cooling the land and even providing oxygen. Cover cropping is one way the gardener can work with, rather than against nature.