By Rachel Foebel, Master Gardener in Training
What are cover crops?
These are plants that are seeded and grown in a specific area for the purpose of covering the soil with plant matter and then allowing that green material (and its roots) to return to the soil by decomposing, thereby feeding the soil and its constituents. Specific crops are used for this purpose as you can choose the cover crop to fit the needs of your soil or the period of time that your garden space is not being used for other crops.
Benefits of Cover Crops
- Covers the soil – preventing soil run off, evaporation of moisture, and suppresses weeds
- Feeds microbial life in the soil
- Creates organic matter for the soil to feed itself with
- Convert atmospheric nitrogen into a form that is usable for plants
- Their roots can loosen compacted soil and allow for aeration as they decompose
Where to use them?
You can use them in any garden space that is not otherwise in use, is about to come out of production or to prepare a garden space for future use. Cover crops are often used by farmers and market gardeners, but can be used in your backyard veggie garden, annual beds, or a garden space you hope to use next year.
Freshly mowed cover crop
Winter-Kill Cover Crops
These are the types that you plant in early fall. They grow to a nearly mature size before winter and then are killed by the frost. They then form a nice mulch over the winter to protect the soil. Choose these varieties in spaces that you want to be able to plant early in the spring.
Oats – Good for suppressing weeds, improving soil health, protecting from erosion. Sow 6-10 weeks before first frost.
Field Peas – Grow well in cool weather, great for nitrogen fixation. Plant about 6-8 weeks before first frost for maximum benefit.
Field Peas in Bloom
Daikon Radish (Tillage Radish) – Most known for its bio-tillage capabilities. The long tap root grows deep into the soil and then breaks down over winter and early spring, aerating the soil, providing organic material for the microbes and can be useful in loosening compacted soil.
Radish Sprouts – I planted these around Sept 3. This photo was taken Sept 12.
Sorghum Sudan Grass – Great for weed suppression and moisture retention in the soil. Be sure to plant when soil is still warm. It will die after frost but if planted too early will go to seed so be sure to mow before it sets seed if it hasn’t been killed by frost yet.
Mature Sorghum (when used as a cover crop you would terminate before this stage)
Cold-Hardy Cover Crops
These are types that you plant in mid to late fall. They begin to grow in fall, become dormant in the winter and re-emerge in the early spring. You then wait for them to develop appropriate bio-mass and terminate before they go to seed. These are usually more difficult to terminate and may require tillage, crimping or tarping. Choose these varieties for a space in the garden that won’t be needed until very late spring.
Rye – Can thrive in low-fertility soil. Very cold hardy. It is recommended to till it into the soil in the spring when it reaches 12-18 in high.
Mature Rye (Should be terminated by crimping or tilling before this stage)
Hairy vetch – Not as great for weed control at first as it is slow growing, but an excellent nitrogen fixator as it is a legume. Plant in early fall and then till or mow it down in the spring and it can remain in place as a nitrogen-rich mulch.
Vetch Flowers
Crimson Clover & Red Clover – If allowed to grow to mid-May in the spring, will provide lots of nitrogen for the soil and provide a spring flower source for pollinators. Has a strong root system that helps reduce compaction.
Crimson Clover
Red Clover
Resources
Field Peas – SARE https://www.sare.org/publications/managing-cover-crops-profitably/legume-cover-crops/field-peas/
Radish as a cover crop – Integrated Pest and Crop Management – UW–Madison https://ipcm.wisc.edu/blog/2011/04/radish-as-a-cover-crop/
University of Vermont – Winter Rye: A Reliable Cover Crop https://www.uvm.edu/vtvegandberry/factsheets/winterrye.html
Crimson Clove Cover Crop Fact Sheet https://www.nrcs.usda.gov/sites/default/files/2024-04/Crimson%20Clover%20Crop%20Fact%20Sheet.pdf
The Peterborough & Area Master Gardeners 