Thursday, September 24, 2009

Winter garden soil improvement

Vegetable garden soils ideally should contain 5% organic matter. If your soil is lacking, boost it during the winter season by planting a cover crop.

Cover crops are grown to produce green organic matter to turn under the soil. Along the Front Range, plant them from September to no later than mid-October. In addition to boosting organic matter, they prevent wind and water erosion over the winter, build soil structure and suppress weeds.

Legume cover crops can add nitrogen to the soil through the action of nitrogen fixing bacteria. It is good practice to buy rhizobium (beneficial root-associated or “rhizo” bacteria) and apply as specified if the seed is not rhizo coated. Rhizobium bacteria are specific for the legume species and are sold with a specific expiration date.

Broadcast the seed/rhizobium mix at the specified seeding rate and water to germinate. If irrigation systems are shut down, hand watering in the fall will help the crop establish before growth slows for the winter.

Winter ryegrass is often used alone as a cover crop (see photo). Winter rye/Austrian pea or a winter rye/hairy vetch mixture overwinter well in Colorado. Winter rye is a quick germinating and pioneering grass. Hairy vetch is a hardier legume than winter pea for the coldest areas. Seed winter rye and Austrian pea at 4 to 6 ounces per 100 square feet. Plan on 2 to 3 ounces of hairy vetch seed for each 100 square feet of garden area.

Note that these green winter plants are attractive to deer and geese. If they are well established prior to extreme winter temperatures, plants generally recover from winter grazing in spring.

When turned under, the decomposing green material can deprive spring vegetables of oxygen if not done far enough in advance of planting. Plan to mechanically till or hand spade under at least two weeks and better yet a month prior to planting. The legumes may have to be tilled several times to kill them and prevent resprouting.

Many gardeners do not have the land area to plant a cover crop for the growing season without depriving themselves of vegetables for a year. Winter cover crops solve that problem.

Consider planting a cover crop this winter to improve your soil.


  1. Your readers with late season herb and vegetable gardens may well find that they will grow more than they can use, preserve or give to friends.

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    It includes preferred delivery times, driving instructions to the pantry as well as (in many cases) information about store bought items also needed by the pantry (for after the growing season). enables people to help their community by reaching into their back yard instead of their back pocket.

    Lastly, if your reader's community has a food pantry, they should make sure the pantry registers on Its free.

  2. Thanks Carl for all the great information. Do you have any suggestions on where in the Denver area one can purchase the cover crops seeds you mentioned? Thanks.

  3. I'm looking for a good Denver-metro area source for winter cover crops, including winter rye. Any ideas for a source with reasonable prices?

    Thanks! Good article.

  4. Several local garden centers carry annual rye. You can also check a major seed company such as Arkansas Valley Seed on Colorado Blvd and I-70 for the annual rye as well as hairy vetch and Austrian pea.

  5. Carl thank you for your insight in a winter cover crop. I recently purchased 5 acres of pasture land that has been over grazed and I am wanting to ammend the whole property to prepare for naturalizing it again with native species and Tress. Would winter rye still be the way to go with a property this size? thank you for your know-how

  6. Cover crops in vegetable gardens are meant to be temporary - grow vegetative matter and turn it into the soil before the plants flower and seed. You are looking to establish a permanent range grass. Here is a recommendation from the Colorado State University Extension website:

    Q. What is a suggested prairie-grass mixture that could be used to seed a small acreage?

    A. The prairie grasses recommended by the U.S. Department of Agriculture Natural Resource Conservation Service for eastern Colorado are: Slender wheatgrass, 0 to 10% of the mixture; western wheatgrass, 20 to 45%; sideoats grama, 20 to 40%; blue grama, 10 to 25%; green needlegrass 5 to 30%; prairie sandreed, 10 to 30%; sand bluestem, 20 to 35%; little bluestem, 0 to 10%. Seed dealers can help design a mix for a specific site using these species as a framework. The final species mix might depend on seed availability and price. It is best to avoid generic "dryland grass" mixes, even though they are often cheaper. Paying a little extra for high-quality seed of the desired species is usually a good investment. Proper seedbed preparation and planting the seed with a grass drill will greatly improve the chances of success, and any type of irrigation will help with grass establishment. A sprinkler that puts out small drops of water would be the best irrigation method, but if this is not possible, flood irrigation can work if care is taken so soil and seed are not washed away. The best time to plant prairie grasses is November through April. If the seed is planted during winter, and spring moisture is good, there is a possibility that irrigation could be avoided. Once the grass is established, it can be weaned from irrigation. Native prairie grasses are adapted to low rainfall and will do fine without irrigation in much of Colorado.

    Consult your CSU Extension county office for additional information. Locate them by checking