What Is a Cover Crop?
Cover crops are plants grown to both cover and improve the soil. They may be used as a living or dead mulch on the soil surface, or they can be tilled into the soil as a “green manure.” Gardeners usually plant cover crops in the fall for winter cover, but some gardeners also use cover crops as part of a summer rotation. Cover crops can be any type of plant but are generally grasses (including cereal grains), legumes, or grass/legume mixtures. Some non-legume broadleaf plants can also be used.
Why Grow a Cover Crop?
Cover crops serve the gardener in many ways, typically by protecting and improving the soil, suppressing weeds, and attracting beneficial insects (Table 1). However, no single cover crop will provide all these benefits since different types of cover crops and management approaches offer different types of benefits. Many gardeners plant a mixture of cover crops to increase the number of benefits to their garden, but cover crops do require some management. Seed must be purchased and planted at the right time, cover crops may need some irrigation during establishment, and the right tools and techniques are needed to terminate cover crops.
How to Choose a Cover Crop?
You should choose cover crops based on which benefits are most important to you and which cover crops best fit into your garden plan. The following information will help you chose the right cover crops.
Benefits of cover crops
- Replace soil organic matter
- Recycle nutrients
- Supply nitrogen (legumes only)
- Protect soil from rain and wind erosion
- Reduce runoff and water erosion
- Reduce leaching of nutrients
- Suppress weeds
- Break up compacted soil
- Attract beneficial insects by providing pollen and nectar
- Reduce disease and nematodes
Cold-hardy cover crops
Gardeners usually plant these species in the fall as winter cover crops, but they can be grown in the summer as well. When choosing species, decide which crop functions are most important to you. Legumes are the clear choice if you want to add nitrogen to your soil, and grasses are a good choice if you want plants that compete with weeds, establish quickly (reducing erosion), or capture available nitrogen left over at the end of the growing season. Grasses are often used in combination with legumes to reap the benefits of both these types of cover crops.
Cereal grains and other grasses
Grasses can include perennials, but most grass cover crops are annuals, such as annual ryegrass and cereal grains like rye, wheat, barley, and oats. These cover crops grow vigorously and can provide quick groundcover, even when the weather is cool. Their extensive root systems grow deep, capturing soil nitrogen that might otherwise be lost to leaching. They also yield large amounts of aboveground plant material when planted and terminated at the proper times. It is important to note that cereals may reduce the availability of nitrogen to subsequent crops if they are planted alone, especially if they mature to the point of flowering or seed set before termination. However, they are very effective at reducing weed survival through competition because they establish themselves very quickly.