Winter Cover Crops - A Fine Time to Build Soil

Winter Cover Cropping: A Fine Time to Build Soil

A Hensley's Seed Co. guide

Once winter arrives, the tractor goes in the shed and the hoes go on the wall, but some tools keep working right through the cold. Cover crops sown in summer and fall protect and build your soil while the rest of the farm or garden sleeps.

Benefits of Winter Cover Crops

Winter cover crops pay off in fall and winter and again in spring. They can:

• Add organic matter and raise fertility
• Hold soil in place and cut erosion
• Smother cool-season weeds
• Improve soil structure and seedbeds for spring
• Help heavy or compacted soils drain better

When choosing a winter cover, think first about spring. If you want a crop still growing in spring, choose winter-hardy species. If your schedule or rotation calls for a clean field in spring, winter-killed species may suit you better. Whether a cover survives winter depends mostly on low temperatures, snow cover, moisture and day length. Knowing your growing zone and each crop's traits will help you choose well for your situation.

Winter Hardy Cover Crops

Winter-hardy covers are cold-tolerant enough to make it through winter. With enough light and warmth they keep growing; otherwise they go dormant until conditions improve in early spring. Their established roots and longer growing period anchor the soil and keep soil life active.

Many hardy covers can be sown late in fall, after summer vegetables come out. Common choices include winter rye, winter wheat, hairy vetch, and several clover. Where winters are a bit milder, Austrian winter peas, annual ryegrassand less hardy clovers also overwinter well.

These crops grow vigorously in spring and need careful management. You can mow and then till the residue into the soil. Or, if you want to use the cover as mulch for summer crops, kill it by crimping, tarping or both in late spring, leaving a thick mat that holds moisture and suppresses weeds. To avoid nitrogen tie-up while the residue breaks down, consider waiting two to three weeks after termination to plant. For more on ending a cover crop, see cover crop termination for organic growers.

Winter Kill Cover Crops

Winter-killed covers earn their keep with the heavy growth they make in summer and fall. The dead residue blankets the soil against erosion over winter yet is fairly easy to handle in spring. Some, like oats, field peas, oilseed radish, and mustard, keep growing late into fall and survive several hard frosts. Others, such as buckwheat, sudangrass and pearl millet , are less frost-tolerant and die back sooner once temperatures drop below freezing.

Mowing the dead residue in spring can help, but often light tillage is enough to work it in before planting, so these fields are ready sooner than fields in a winter-hardy cover.

Since their value comes from the biomass they build, winter-killed covers must be sown early enough in summer or early fall to grow substantially. That usually means sowing after spring crops or undersowing them into a standing crop such as corn or brassicas.

Winter Cover Crop Seed Mixes

Many growers deliberately combine winter-hardy and winter-killed species to get the advantages of both. Fall Green Manure Mix follows this approach for northern growers: the peas, clover and ryegrass die over winter, and the rye and hairy vetch resume growth in spring.

You can also blend your own mix for your zone, adjusting the proportions to suit the season and field conditions.