It’s beginning to be that time of year again, when our vegetables gardens become less productive and most of the season’s bounty has been realized.  Before you begin to look toward next year’s plans, why not consider planting something for the winter season?  A hard-working cover crop is the perfect selection to fill in your garden and improve soil for next year.

A cover crop is a crop that is grown for protection and enrichment of the soil rather than for harvest.  Since they are not harvested for use as food, growers plant them for other valuable qualities they provide while in the ground.

Historically, cover crops were used by Native Americans and the Founding Fathers (George Washington and Thomas Jefferson were regular cover croppers).  They were used extensively in modern agriculture all the way up until the World War II era, when the advent of synthetic fertilizers virtually eliminated their use. 

In recent times, cover crops have made a comeback among folks looking toward more sustainable agricultural systems.  Sola Gratia Farm in Urbana focuses on sustainable agricultural practices without the use of synthetic fertilizers and pesticides. Hunter DiFonso is Farm Manager at Sola Gratia and plans a regular rotation of various vegetable crops and cover crops.  “Our main considerations when using cover crops are adding organic matter to the soil, weed suppression and reducing soil compaction,” said DiFonso.  On recent visit to their farm, I saw several cover crops in action, including oats, winter peas, Sudangrass and buckwheat. As we toured the fields of cover crops, DiFonso explained, “Since we don’t use synthetic fertilizers, cover crops are one of the ways we keep soils productive.”

Above the ground, cover crops provide protection to the soil from pounding raindrops and howling winter winds.  Winter hardy varieties form a dense cover as spring progresses and block out weeds until they are mowed or tilled under prior to planting of spring crops.

Below ground is where these valuable plants provide the greatest benefit.  Some cover crops, such as clover and peas, are nitrogen fixers and will actually add this limiting plant nutrient to the soil.  Others, such as buckwheat, annual rye and winter wheat will scavenge nitrogen available in the winter soil (some of which would otherwise be lost to leaching) and bind it up within their plant parts.  Upon tillage in the spring, microbes in the soil will begin the decomposition process, unlocking nutrients for next year’s crops.  

Many of these species have been noted for their soil structure building capabilities.  Sudangrass’s extensive roots loosen soil and build structure all the way down to subsoil.  However, cover crops in the brassica family (including certain varieties of turnips and radish) are probably the most impressive.  Not only do these plants scavenge nitrogen, but the large roots relive soil compaction as they develop and quickly decompose after being turned under, returning up to 200 lbs/ac of total nitrogen.

Cover crops may be planted as soon as vegetable crops are harvested.  The seeds are often available at local garden centers or they may be purchased online from out of state sources.  You can prepare the planting area with tillage or use no-till methods.  Most cover crops require planting 4-6 weeks prior to cold weather that will limit winter growth.  So, right now is the time for sowing seed.  Some of the larger-seeded varieties, such as wheat, oats and hairy vetch may be hand-seeded into closely set rows, while the smaller-seeded varieties, such as buckwheat, clover and ryegrass, may be broadcast on a prepared soil surface and covered with a thin layer of soil.  Some varieties, such as the tillage radish, will succumb to freezing temperatures and die over the winter. Whereas, winter-hardy varieties will continue growth in the spring as things warm up.  Unless flowering is desired, mow the cover crop before it goes to seed.  About 4 weeks prior to planting new vegetable crops, till the cover crop under to allow soil fauna to begin the process of working their magic and return captured nutrients to the soil.

For more information on individual cover crop characteristics and planting dates for our area, please see the Selector Tools developed by the Midwest Cover Crop Council and available at www.mccc.msu.edu.

Ryan Pankau is Horticulture Extension Educator with University of Illinois Extension serving Champaign, Ford, Iroquois, and Vermilion Counties.