Green Manure Cover Crops

Austrian Winter Pea

Since I first started gardening, I've always tried to grow cover crops. They are an easy way to ensure healthy and fertile soil.

The idea is that in addition to the three elements found in any conventional fertilizer (Nitrogen, Phosphorous, and Potassium), soil needs plenty of organic matter. The organic matter, which is basically decomposed plant life, is filled with other minerals, helps the soil absorb and hold water (but not too much!), and generally makes life worth living for our plant friends.

When you just toss in a chemical-based fertilizer, you're giving your plants the basic N-P-K they need to survive, but your soil health will gradually deteriorate, beneficials like worms will find it harder to thrive, and your plants will get less and less happy, tasty, and nutritious over the years.

Now, a good gardener could and should work lots of compost into the soil every year to get a good mix of organic matter into your soil. I do a certain amount of this, but our family doesn't really produce enough compost to make the garden happy and I'm not big on seeking out alternative sources.

It has always seemed much simpler to just grow a cover crop. Flip through the seed catalog to find something that looks right, place the order in the Internet, and a week later the seeds arrive at your doorstep. Plant them when the time is right, watch them grow, and work them into the soil to complete the process.

Right now I'm growing a couple varieties of peas because they're hardy enough to go into the ground in early spring. In the past, I've also grown varieties of wheat, beans, clovers, and vetches. You mostly see Field Pea in the photo to the left with some Austrian Winter Pea in the background. I planted them the weekend of April 12th and watered them daily through a hot dry week because I had been too lazy and time-pressed to make sure they were deep enough in the soil to stay moist. Thankfully, Grandpa Bill visited at the end of the week, bought a few bags of topsoil, and covered them up. Four or five days later, they were sprouting through the soil and they've been thriving ever since. These pictures were taken May 10th.

As legumes, the peas are diligently fixing nitrogen in the soil that will be available for other vegetables to feed on all summer long. Additionally, after I work them into the soil, the foliage and roots will decompose and provide that all-important organic matter the soil needs. I dug up the first patch of peas to put my overwintered rosemary plant back into the garden. It's probably time now to work the rest of it into the other beds and let it decompose a bit before planting everything else. I just need the time to do it!

Like a few other things in life, there's still plenty more I'd like to know about cover crops. I'm especially interested in timing. I try to plant some in the early spring and work them into the ground before planting tomatoes, peppers, beans, and such in late May/early June. I also usually plant some in mid-late summer in the bed where garlic or peas were earlier harvested. But when is the ideal time to plant? Is it better for the cover crop to die off over the winter before working it into the soil? Is it possible to plant your vegetables too soon after you've worked your cover crop into the soil? Umbra tackled a portion of this question last week in Grist. Anyone else have answers?