Cover crops have many benefits for the garden. A cover crop is simply a plant grown, not to harvest, but for its benefits to the soil. You can grow cover crops anytime that you have a spot in the garden that doesn’t have a crop growing in it. Fall and winter are a great time to have cover crops in St. Louis, as the garden is usually bare unless you are growing some type of overwintering crop like garlic.
Cover crops have the ability to improve soil quality by adding organic matter and nitrogen. They also cover the soil surface, meaning less erosion and fewer weeds will germinate. Possibly the biggest benefit that cover crops have is that they feed the beneficial microorganisms in your garden soil. These organisms feed off the compounds that living roots exude into the soil and dead organic matter as mulch. Feeding these organisms improves nutrient availability and soil structure, making it easier to dig and easier for water to absorb into the soil.
In the past we have offered several types of cover crops made of single species or a blend of two species but increasing research on cover crops has shown that having more species in your mix increases the benefits of cover crops. In addition, our increasingly warm winters have meant that cover crops that used to be killed by the winter are now surviving the winter more years than not. Due to both of these facts we have changed our cover crop offerings to just two blends to simplify things and increase the effectiveness of the cover crops.
The first blend is the “winter kill blend.” This is a blend of 4 species of cover crops that were selected to die when the coldest part of winter comes. This type of cover crop should be planted in September so there is enough time for the cover crop to grow before the cold kills them. The winter kill blend can be a great choice if you don’t want to have to worry about killing the cover crop in the spring. It is also the best option if you want to plant cool season crops where the cover crops will be growing. This blend includes oats, berseem clover, phacelia, and tillage radish. Oats are particularly good at adding carbon to the soil and feeding beneficial organisms. Berseem clover is one of the best nitrogen fixers so it can add fertility to the soil. Phacelia blooms over a long period, helping to feed and sustain beneficial insects in your garden. Tillage radishes wide arching leaves help to quickly cover the soil, reducing weeds, and their large tap roots help to break up compaction and increase water infiltration.
The second blend is our “overwintering blend.” The “overwintering blend” is a combination of 4 cover crops that were selected to reliably survive our winter. Overwintering cover crops can be a great choice if warm season crops are more important in your garden. This blend can be planted as late as mid-October, right around when you are ripping out your warm season crops. It then grows throughout the winter and spring and is ready to be killed or removed around the end of April, just in time to plant your warm season crops again. The 4 species of this blend are annual ryegrass, winter rye, crimson clover, and winter peas. Annual ryegrass creates a short dense turflike growth with a dense mat of roots holding and covering the soil, reducing erosion and weed germination. Winter rye adds an enormous amount of carbon to the soil and provides support to the winter peas. Crimson clover adds nitrogen to the soil and produces flowers to feed beneficial insects in the garden. Winter peas also fix nitrogen in the soil while also being edible. The tender growing tips of pea plants are delicious all winter long.