The land our house is on was once rich prairieland, teaming with clover, thistle, ragweed, milkweed, aster, sedge, coneflower, rye, sunflower, etc. These plants grew and died, creating the rich tilth that we think of as central Illinois soil today. But the black earth that we see driving around late fall after the harvest isn’t the same organically rich earth that it once. When the green manure those wild plants represented is no longer allowed to grow and die, the cycle that eventually reaches a climax of organically active biomass is broken.
But gardeners can take steps to return some of the biomass to their beds. Green manure, also known as cover crops, keep weeds out, fixes nitrogen from the air into the soil, adds organic matter, reduces evaporation, and even helps control disease and fight pests. Some cover crops are cold tolerant and will grow past the first frost before dying when the deep cold of winter hits. At that point the plants begin returning their organic matter to the earth. Other crops will overwinter and begin growing the following spring, continuing their work fighting weeds and disease, fixating nitrogen, etc.
The only downside to cover crops is that for green manures that overwinter, new seeds won’t grow for two weeks after the young crop is mowed and turned under. This is because teams of beneficial microorganisms get busy for those two weeks breaking down the plants, breathing in oxygen and releasing carbon dioxide at such a high rate that seeds won’t germinate. This is just the kind of activity that naturally leads towards the black gold earth that was historically found in our area! Or if the overwintering crop is allowed to mature a bit more and become starchy, it will take five weeks for the microorganisms to do their thing and settle back to a maintenance level that allows seeds to germinate. A wet spring, then, can really slow things down when you can’t get right to turning under that green manure.
I’ve decided to plant a fall green manure mixture from Johnny Seeds in two of my six beds this year. The one is where my corn grew this year and where the potatoes will grow next year. I can’t plant the potatoes until the soil is dry enough to dig furrows anyway. I’ve also planted the mix in the bed with the last of my zucchini, where I’ll be growing my greens and brussel sprouts next year. I’ll plant the late winter lettuce and spinach under the hoop house in another bed, and will plant my spring peas in with the overwintered cover crop before turning it all under for the main green crops of summer.
Check back next spring and summer to find out how my experiment works. In the meantime, start your own experiment with green manures. There’s no better way to move towards a healthier organic garden!!