Cover crops are typically short-term crops grown in between main garden (food) crops to provide nutrients and increase organic matter in the soil. Incorporating cover crops into your garden planning calendar can be pretty simple or you can go through a great deal of planning. In any case, at least a little bit of planning is definitely helpful.
What are some benefits of growing cover crops? They protect the soil from erosion, lower the soil temperature and help retain moisture – a lot like mulch functions. In fact, cover crops are considered living mulches that also reduce soil splash and suppress weeds, and in doing so reduce potential diseases in the garden. They improve soil texture and porosity, fertility, and water-holding capacity. They can interrupt pest and disease cycles and provide mulch. Some cover crops support ecosystems and biodiversity by flowering and providing habitat for pollinators and beneficial insects.
Some common cover crops include cereals (rye, wheat, oats, barley), grasses (ryegrass, teff, millet, sudangrass), buckwheat, sunflowers and brassicas. These will help increase organic matter in your soil (and thus compaction relief), nutrient accumulation and biomass production, provide weed suppression and improve biodiversity through pollinator/beneficial insect support. An example: in late summer you plant ryegrass, rapeseed or oats, which grow fast in cool weather. In early spring they will have died over the winter, and you can turn in the dead plant material and plant your food crop. It will thrive with the increased organic matter and beneficial microorganisms, and face fewer weeds.
Another type of cover crop are green manures. These are legumes such as true clovers, sweetclovers, vetches, lentils, peas, beans, soybeans, and sunn hemp. Leguminous crops fix nitrogen, that is they convert it from an atmospheric gas into a form the plant can use. For instance, in very early spring a gardener might sow a green manure and let it grow until a couple weeks before planting their warm season vegetables, many of which are high nitrogen users. The green manure has just added a very important nutrient (nitrogen) into the soil that will be of immediate use to the tomatoes, peppers, cucumbers, etc., that are planted next in that bed.
What is your goal in planting a cover crop? If it’s to add nitrogen then consider legumes listed above. If you wish to support pollinators and beneficial insects plant a flowering crop such as buckwheat, phacelia or clover. Seed mixes are another option and easily available, sometimes offering more bang for your buck.
It’s easy to broadcast seed in small beds by hand and turn the plant material over manually – no need for drills or rototillers. However, weed whackers can be useful to chop up plant material before incorporating into the soil.
Sowing thickly ensures less weed competition.
Watering to establish plants is important, but becomes less so as they grow.
Fertilizing will help produce greater biomass but is optional.
Typically cover crops are sown early or late in the season whenever a bed is inactive, or between rows. It’s not necessary to sow an entire garden in a cover crop – sowing individual beds is often easier.
Cover crops can assist the gardener with crop rotation for an entire season by not planting a food crop and sowing a cover crop in its place. In this way you are adding another year to the number of years between food crops of a single family, and using that year to improve your bed. If this is your aim be careful what type of cover crop you are planting as some may belong to one of your food plant families (e.g., brassicas or legumes). This will thwart your crop rotation plan.
Don’t allow cover crops to self-seed unless you want a second crop immediately. Mow them down if they get ready to flower.
If the cover crop isn’t dead yet when turned into the soil, wait a good two weeks before planting. The finer it’s chopped up before incorporating, the faster it will decompose. You want it to be mostly decomposed before planting.
It’s easier to turn in a dead crop in spring than to chop down a live one. Note: some cover crops are perennial and begin growing again in spring so be aware if yours will winter-kill.
It’s best to research a few cover crop options before deciding which you will sow.
Some cover crops are perennial, some annual, some thrive in cooler weather and some do well in heat. Based on the time of year you wish to plant as well as your overall goal, select your crop carefully. Consulting a tool such as the Midwest Cover Crop Council’s web-based Selector Tool may be helpful. https://www.midwestcovercrops.org/selector-tools/
Helpful foresight: Winter rye and ryegrass have allelopathic properties that make it difficult for small seeds to germinate after the bed was sown with these cover crops.
There are many resources out there, but some outstanding ones that were used for this article include:
Johnny’s Selected Seeds Grower’s Library: select Grower’s Library from the menu, then Videos or Webinars (there are lots of both on cover cropping).
University of Minnesota Extension: search “cover crops” for many options.
Good luck exploring this relatively simple way to improve your garden and the ecosystem!