As summer fades to fall and your crops begin to falter, it’s a great time to take an important step to improving your garden for next year – planting a cover crop.
Why Cover Crops Matter
From the Washington State University Extension, there are many benefits to incorporating a cover crop rotation in your garden, such as:
- Replace soil organic matter
- Recycle nutrients
- Supply nitrogen (N) – 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
Investing a few dollars in seed, and a few minutes in planting, will pay off in rich and healthy soil next spring.
Choosing a Cover Crop
There are many choices of cover crop – grains like wheat or rye for weed control and tilth, legumes such as clover and vetch for nutrients, brassicas like arugula or mustard to act as a biofumigant. Some need to be tilled in before planting in spring, others can just be chopped down and planted through for no-till gardening. Choose a cover crop that fits your gardening goals – or even better, blend two or more for a broader range of benefits.
The better established your cover crop, the better it will grow into the spring, so plant as early as possible. Don’t wait for the whole garden to be empty – as individual plants finish, pull them out, rake the debris, and scatter a handful of cover crop seeds right away.
Grain Covers
Barley – Fast growing cover offers good weed suppression, deep soil effect, some insect and disease suppression, nutrient scavenging that includes N, P, and K. Flowers early, so needs to be worked into the soil early. May be less winter hardy than other grain cover crops.
Oat – Very quick cover for weed suppression, also gives some benefits in soil structure and nutrient scavenging. One of the easiest grains to work – can be fall planted (sow in August) and let winter-kill, then tilled in spring; can also be spring sown and worked in just before seed set in late spring/early summer.
Rye – Rye grain- annual rye grass is different! Very good weed suppressor, and one of the best covers for breaking up heavy soils and improving tilth. Very good at scavenging N, P, and K. Can be planted late, but better nutrient scavenging when planted early. May inhibit crops – should be tilled in three weeks before planting to decrease allelopathy and nutrient tie-up. Can grow fast in spring, making it hard to work, but doesn’t seed early.
Wheat – One of the most balanced grain covers, does a good job of weed, disease and insect supression, scavenges N, P, and K reasonably well, improves soil workability. A bit slower to take off in the spring, it works in easier than rye. Work in two weeks before planting to decrease nitrogen robbing.
Legume Covers
Clover (annual) – Crimson clover doesn’t runner like perennial clovers, and is easily controlled by tilling. A very balanced cover that both fixes and scavenges N and reduces erosive losses of P and K. Often the preferred cover where it can be used, but dislikes wet or acidic soils. Can be mechanically killed (hoed) and planted through for no-till. Can plant transplants immediately, but wait two weeks before seeding after killing or incorporating.
Fava – An impressively massive cover, can reach five feet before flowering in spring. Favas offer good biomass, good N fixing, and fair weed control. Must be seeded early, and not very winter hardy (about 10۫ F), but will tolerate wetter and poorer soils than clover.
Field Pea – Austrian field peas provide very high levels of N fixing and biomass, but don’t run deep roots to capture lost nutrients or break soil. Despite the volume of leaf and vine, they are rather succulent and work fairly easily. Let them mature in spring through full bloom to provide early food for bees and to maximize N yield, then incorporate. Tolerate cold and wet soils.
Vetch – Hairy vetch is an excellent source of fixed N, and though slow to start off in the fall it races ahead in the spring, rapidly smothering weeds. Vetch can help suppress insects, and of the legumes is the best scavenger of P. Because of its easy mechanical kill and short residue lifespen, it is an ideal cover for no-till transplanting, though a bit thick to seed through right away. A significant amount of vetch seed is “hard”, and can remain ungerminated the first year to sprout as a “weed” in following seasons.
Have more questions about cover crops? On our YouTube channel we have a short video and a class recording that dive deeper into using cover crops to boost your gardens productivity.
