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Cover Crop as Green Manure: What it is & Why we do it
You don't need to add compost to your soil every year. You can grow it.
Growing crops for food takes a lot of energy. Energy from the sun, the soil, from water - vegetable and fruiting crops consume and rely on a lot of organic matter to thrive. That’s why healthy soil is SO important to cultivate, especially if you’re growing in the same spot of earth year after year.
Every winter, I sow cover crop in my gardens across the city. Cover crop is just that - a crop that covers the soil. This lessens soil compaction from rains, keeps soil light and loamy, as roots make space for air flow and reduces erosion. Cover crops are also used as a green manure - we let them grow and then cut them down, allowing them to rot and create organic matter in our vegetable beds.
I recommend a blend of crimson clover and field peas - you can pick up seed at most nurseries locally. You will also see vetch (I like!), cereals (rye, oats, etc) and faba/favas as cover crop seed. All of these are great, but cereals are tough to cut down and take longer to break down in spring, whereas the clover and legumes (peas) being tender-stemmed, are fast to decay once they’re cut into small pieces and turned into your soil.
This decomposition is the “green manure” part of cover crops. It invites healthy decomposers into the soil and is a sort of on-the-spot composting system.
In mid to late autumn, clear your beds of any lingering vegetables. Evenly broadcast sow a light sprinkle of seeds over the garden beds, and simply fork it in with a bow rake. That’s it!
Crimson clover need only be shallow-seeded, as it’s small and will germinate. Field peas or faba/fava will need to be forked in a bit deeper. It will all be very intuitive when you see/feel the seeds. One pound of crimson clover covers about 500 square feet of bed, so if you have a 4’x8’ garden bed, that would require about 1 ounce of seed. A little goes a long way! I always ALWAYS have left over cover crop, so this is a good seed to share with friends.
Traditionally, we till in cover crop immediately upon flowering and before the stems thicken and seeds develop, in early spring. In the Pacific NW that happens right about April. I will often till and turn the cover crop earlier, if I want access to the beds, and file that under “better-than-nothing”. It really depends on which cover crop you choose, as well.
WHICH COVER CROP SHOULD YOU PLANT:
As I noted, I choose crimson clover and field peas, as they are easy to cut down in spring and break down in the soil quickly. Clover is also a MAJOR bee-friendly crop, and I love offering some early food to the bees after their winter hibernation. There are many others sold and to choose from: Rye, Vetch, Oats, Dutch clover, White clover, Favas (not the broad ones we eat, but small-seeded favas that are round, like peas), Buckwheat (this actually gets planted as a spring or summer cover crop), and more. If you really want to dive deep or have a question about a particular cover crop, hit me up in the comments. I’m sparing the research-style article here, as I tend to think it’s TMI to damn near anyone but me :)