September is a good month to plant cover crops in your garden. There are a wide variety of cover crops that can do a variety of things to benefit your garden soil or your garden's produce. Some are better at enriching the soil, some are better as mulch, or keeping weeds out of your garden or providing air space in you soil so your plant roots can grow. Some are better at providing fall flowers for native pollinators, and some can provide mulch when simply cut down.
At a recent Master Gardener Regional Conference, Annie Klod put on a class on cover crops and I would like to share some basics from that class.
One very important aspect of cover crops is that you have to cut and essentially kill the cover crop before it goes to seed. It is generally beneficial to leave the roots in the soil (except perennials) and keep the greens to either incorporate into the garden or use as a mulch there.
Nitrogen is one of the key chemicals that a garden needs and that is relatively short lived as it readily percolates downward in the soil and is used by many plants. It is for this reason that plants that provide nitrogen first got my attention. Phosphorus and potassium are relatively stable in soils. Field peas, clover and cow peas are very good at providing nitrogen. I plan in using crimson clover in the near future. Crimson clover (not red clover) can be planted in September and will be killed by a temperature of about 10 degrees below zero. This will prevent carryover as long as seeds are not produced.
Simply leaving the roots of your regular peas and beans in your soil will also help add nitrogen in your garden soil.
Rye can help suppress and/or outcompete the growth of many weeds, including dandelions and thistle. Rye can be planted very late—even well into October. Annual rye is preferred as a cover crop. If you use one of the grasses, grains or oats use just annual versions of these.
Buckwheat is an interesting cover crop to me, as the flower attracts hover flies. Hover flies are also called flower flies. Hover flies as adults are pollinators, and as nymphs eat such things as aphids and thrips. My strawberry patch was infested with thrips, so I have a couple of plantings of buckwheat now. Buckwheat can be cut a couple of times for mulch before it is tilled into the soil (don't let it go to seed).
If you want to plant a perennial cover crop to help build up your soil, a good combination is fescue grass with a perennial clover such as a white or red clover—not crimson clover.
Cover crops such as radishes can help to reduce soil compaction. Just remember to cut them and/or kill them before they produce seeds.
The University of Minnesota Extension website has been updated to make finding information like this much easier. Simply type your subject in the search box when you open the Extension page—www.extension.umn.edu. For broader information go to "Learn About," and click on "Yard and Garden." Dial (218) 444-7916 to reach the local Master Gardener voicemail to get help with your gardening problems.