Andrew Fritz, Urban Agriculture Conservationist
Planting cover crops between August 15th and September 15th is ideal. However, depending on fall temperatures, they can be planted as late as October 1st.
This means you will need to “interseed” or “intercrop” within your late summer or early fall vegetables. After weeding for the last time of the year, create furrows in the soil approximately ½” to 1” deep with a hoe, lightly sprinkle your cover crop seed into the furrows. Then cover the seed with soil thereby burying the seed. The cover crops will germinate between your vegetables and not present any issues to growth.
You can also broadcast the seed evenly over your garden and rake in.
Will I need to water cover crops?
If the weather is hot and dry in August and or September, then it may be necessary to water your cover crops to ensure good germination and growth. Otherwise, cover crops will grow well without much attention to water needs.
What happens if they produce seed?
If planted too early, oats may produce a seed before they die due to frosts. In this case, it is best to cut the tops of the oats off as they are flowering but before they produce seed. Crimson Clover, Cereal Rye, and Hairy Vetch will not flower until sometime early to mid-spring. They will need to be cut down as they are flowering but before seeding.
If they produce seed it is likely best to cut and remove the plant to limit weedy issues in the garden. However, some gardeners are okay with this as a cover crop in the midst of your vegetables is not inherently bad. In fact, it can be beneficial.
What do I do if I want to plant early spring vegetables and the cover crops aren’t ready?
There are a few options to accommodate for this.
Option 1: Plant Oats
In the area you plan to grow early spring vegetables, using oats as a cover crop is ideal. Oats will die during the winter.
Option 2: Row Method
Plant the cover crops in rows so that you can then plant your vegetables in-between the rows of cover crops in the spring. The cover crops would then need to be cut while they are flowering to terminate. However, planting between cereal rye is not advisable due to its allelopathic properties that suppresses most vegetable growth.
Option 3: Tilling
The least preferred option as it relates to soil health is tilling. Tilling in the cover crops within the area you’d like to plant your early spring vegetables will terminate the cover crops with the exception of cereal rye which may return in small amounts.
Terminating (i.e. killing)
There are several ways to terminate cover crops. The best method for many gardeners is the “cut and cover” method. At your convenience, but ideally when the cover crop is flowering (for the greatest soil health benefits), cut down the cover crop with shears, hedge trimmer, mower, etc. and cover with an opaque material like black plastic or opaque landscape fabric to stop photosynthesis. This will also suppress early annual weeds.
Other options of terminating include tilling (though cereal rye may still come back in small amounts), herbicide application, and cutting at the most vulnerable moment for the cover crop which is usually when it is flowering. Cereal rye can be “crimped” with a special tool but is not practical for many smaller gardens.