by Diana Alfuth, horticulture educator for Pierce and St. Croix counties UW-Extension
As you harvest your vegetable garden, there are things you can do to improve your soil for better crops next year, including planting cover crops! Cover crops, sometimes called green manures, are relatively fast-growing plants that improve the soil’s physical structure and fertility.
Seed cover crops into areas as you harvest your vegetables. As they grow, they act as reservoirs for plant nutrients, such as nitrogen, phosphorus, and potassium, as well as micronutrients. When worked into the soil, cover crops return those nutrients to the soil, making them available to future vegetables crops. They also increase organic matter to improve the soil’s overall physical structure. Cover crops in the pea (legume) family are able to convert nitrogen from the air into a form useable by plants. Cover crops also reduce bare soil, which helps prevent soil erosion and weed growth.
|Cover Crops for Late Summer and Early Fall|
|Cover Crop||Seeding Rate||Comments|
|for 100 Sq. Ft.|
|Oats||4 pounds||Medium growth rate||dies in winter|
|Field Peas||5 pounds||Fixes nitrogen; outcompetes weeds||dies in winter|
|Oilseed Radish||1 pound||Fast growth rate; breaks compacting||dies in winter|
|Winter Rye||4 pounds||Fast grower; can be planted late|
|Annual Ryegrass||1 pound||Fast growing||dies in winter|
|Winter Wheat||2 pounds||Fast growing; not for low pH soil|
Which cover crop is best for your garden depends on your needs. While some cover crops should be planted early in the growing season, cool-season cover crops are planted in late summer to early fall, early enough so that they establish some growth before winter. Some crops will be killed by freezing temperatures, while others will go dormant for winter and begin growing again in spring. Those that are killed by freezing, such as oats, are good for use in areas where you will do an early spring planting of cool-season vegetables. If warm-season vegetables will be planted, cover crops, such as winter rye, which will resume growth in spring, may be a good choice.
To get the most from your cover crop, mow or till the plants before they flower to keep them from storing nutrients in their seeds and to prevent self-seeding in your garden. After working the plants into your soil, allow at least a couple of weeks for them to decompose before planting your vegetable crops.