Improve soil with fall cover crops

Lauren Bethke

As the growing season winds down in the Twin Cities, many gardeners focus on pulling plants, raking leaves, and putting beds to rest. But instead of leaving garden soil bare, planting cover crops in the fall can protect and improve your soil through the winter months. Read on for information on cover crops, how they can benefit home gardeners, and tips for choosing and planting.
Cover crops are basically living plants grown to benefit the soil, not for harvest. Over the winter, wind and precipitation can wash away topsoil and nutrients when the soil is bare. Cover crops act like a living blanket, holding the soil in place, feeding insects and microbes, and soaking up leftover nutrients that might otherwise wash away. In spring, the organic matter from these plants is worked into the soil, adding nutrients and improving soil texture for the next growing season.
There are several species of plants that can work well as cover crops in our northern climate. Timing-wise, you will be planting the cover crop after you clean out your garden beds in the fall, and it will either die over the winter or you will cut it down early in the spring, before it goes to seed. So your cover crop needs to grow quickly and be fairly hardy in order to have enough time between the fall harvest and the first hard freeze to put down roots and create some organic matter in stems and leaves.
Oats are fast-growing and easy to find, making them a good choice for gardeners new to cover crops. They sprout quickly in cool soil, grow until winter, then naturally die after a hard freeze, leaving an easy-to-work garden bed in spring.
Winter rye is another good option for Minnesota. Rye germinates in cool soil, survives the winter, and resumes growth early in spring, protecting soil and competing strongly with weeds. It has deep roots that can help break up compacted soil. It can be tilled in or cut down in early spring.
Field peas are a legume, meaning that they are particularly efficient at fixing nitrogen from the air and naturally enriching the soil. They will die over the winter in Minnesota but still provide great ground cover and organic matter.
It’s starting to get a bit late in the season to plant cover crops this year, so you could also consider a quick cover crop in early spring for a lot of the same benefits in terms of nutrients, soil structure, and organic matter. Oats, annual ryegrass, or red clover are a few species that can be planted in early spring and will grow for a few weeks before you till them in to the soil and plant your main garden. If you take this approach, make sure to use some other mulch over the winter to protect your soil from wind and erosion.
For best results, you can also mix species. A combination of cover crops can provide multiple benefits as each plant has different timing, structure, and organic makeup.
To plant cover crops, first clear the area of plant debris and lightly loosen the soil. Then, scatter seeds and rake them in to about a half inch deep. Water well until the ground freezes. If your cover crop dies over winter, you can simply rake away residue or till it in to the soil once it warms up. For overwintering cover crops like rye, plan to cut them back in early spring. Let the cut plants dry for a few days, then either till them lightly into the soil or leave them as a mulch layer. That’s it – using cover crops is pretty simple!
The most common mistake home gardeners make when using cover crops is letting them go to seed. It’s important to cut down cover crops early in the spring so they don’t become weeds themselves!
For Minnesota gardeners, fall cover crops are one of the simplest ways to keep improving your soil year-round. Spreading a few handfuls of seed in the fall can mean healthier soil, fewer weeds, and better harvests next summer.
For more information, check out the University of Minnesota Extension Yard and Garden website. Extension resources are written by experts and contain the latest and most reliable research-based information. Happy gardening!