Here’s a useful article from mother earth news on mid season cover crops. Give it a try!
Update 8/10/14: After reading this article I did some thinking as I visited the beds, trying to imagine what I might do better regarding cover crops. In my beds with spinach, lettuce, swiss chard, beets, arugula, kale, etc. I practice what is essentially a square foot gardening approach, something I first began practicing between our small Highland Park, NJ, apartment and the sidewalk to maximize what I could grow. Since I don’t do rows, there’s little opportunity to plant cover crops between the rows, but that’s the point of square foot gardening — it’s its own form of cover cropping. But further, in reading through Johnny’s Seeds I noticed that turnips are listed as a Farm Seed used as a cover cropping. I’m now thinking next year of mixing in one or two pea plants and later soybeans into the mix to fixate nitrogen and add more biodiversity.
I’ve been also using Eliot Coleman’s The New Organic Grower to do some cover crop research. Next year I’m going to pull the basil, oregano, and rosemary to the outside of the bed, inline with the tomatoes for which they are beneficial plants. This will allow me to plant alfalfa, ryegrass, and oats.
The peas between the early and mid-season potatoes worked well for a cover crop between rows. I think next year I’ll add buckwheat between between the late potatoes which then will be smothered out once they get big (which is what they did with the beans I planted between the late potatoes this year. The buckwheat can be cut back and given to our livestock.
Coleman recommends undersowing squash with sweet clover between the rows. This will smother weeds and fixate nitrogen this year, and will also help beets, carrots, and other root crops next year. Since onions don’t grow well following a green manure, he recommends planting the onions where they squash grew the year before. Sweet clover is a good choice for my cabbage bed (brussel sprouts, kohlrabi, kale, chinese broccoli, etc.) since the tap root (primarily straight down, deep, root) of the clover doesn’t interfere with the shallow-rooted brassicas. (Speaking of root patterns, I’ve been using Steve Solomon’s Gardening When It Counts to view those patterns, thanks to his helpful diagrams in the second half of the book.)
It may not be intuitive at first glance, but soil isn’t depleted because it’s growing something. Indeed, fallow soil quickly looses its nutrients, humus, and microorganisms and becomes just dirt. Also harmful is growing the same thing, and only that one thing, in a space. The goal is to experiment in your garden until you find that reasonable balance of complimentary plants, rotation cycles, and aesthetics that work in your yard. The good news is nature doesn’t have “the right plan”, just a plethora of ongoing experiments that are ever changing.
In Braiding Sweetgrass biologist Robin Wall Kimmerer describes her journey to rediscover the indigenous knowledge of her ancestors. She is discovering the love and language of plants and earth that we can learn to sense — not in a scientific way but something more intimate — that compliments scientific knowledge. As in all loving relationships, we give 100% and receive 100% in return. But further, we are each changed and begin to take on characteristics of the loved ones, as they do of us. Just as this happens in a loving relationship between two adults through different lived experiences together, so too I’m finding the work in the garden isn’t a scientific endeavor but one of lived experiences with creation that I’m coming to love, and be loved in return.