Cover Crop by Wayne Bowman, Master Gardener.
In an earlier column, I wrote about putting the garden to rest for the season using compost and mulch. An alternative to that method is the use of a winter cover crop. Many of you might consider cover crops to be something only used in commercial fields after the harvest of the cash crop, but there are benefits to be had for the smaller garden, too. After your harvest, cover crops can nourish your garden, protect it against erosion and weeds, and loosen the soil.
Cover crops can be listed in two categories, Legumes and Non-Legumes. All, however, provide the previous benefits, but in varying degrees.
Legumes, red clover, hairy vetch, field peas, and others are great for fixing atmospheric nitrogen for use by subsequent crops. Lower carbon and higher nitrogen in cover crops promote a faster breakdown in the soil. While they release the needed nitrogen faster, legumes provide less weed control and add less organic matter to the soil.
Non-Legumes– rye grass, winter rye (which is actually a grain), wheat, and oats all produce significant biomass, soil conditioning, and excellent weed and erosion control. Due to their higher carbon residue, they do take longer to break down in the soil, so nutrients that they scavenge from the soil will not be available to your next crop as quickly. The advantage of the slower decomposition comes in the form of the increase in soil organic matter.
A good cover crop sends roots deep into the soil. After the plant decomposes, this loosens the soil, providing pathways for moisture and air to your plantings. The dense top growth crowds out weeds, and in the case of non-legumes, competes with the weeds for nutrients. Some of the non-legumes also produce allelochemicals, which are natural herbicides. While these don’t affect all plants, it’s best to allow the roots of them to decay for a couple of weeks before planting.
Green Manure isn’t what you’ll find in the bottom of an alien spacecraft, rather it’s the term for a cover crop used to further nourish the soil. Used in various ways, the crop may be cut down while green and tilled in, cut and left to lay as mulch, or allowed to die and decompose in place. A drawback to allowing it a natural death is that plants will normally seed before the end of their life cycle. This gives it the potential to become a weed instead of a benefit to your garden. For this reason, most cover crops are cut before they mature.
Leaving the dead stubble and top growth in place allows no-till gardeners to plant directly into the covered areas by opening planting holes in which to place transplants. A small trench dug through the cover accommodates row crops.
Better moisture and heat control, decreased compaction and increased nutrients are all benefits and reasons why the next time your harvest is complete, you should try a cover crop.