Green manure is a crop that is planted in the fall; its purpose is to improve soil fertility and tilth in the spring. I have just seeded a fall green manure mix from Johnny’s Selected Seeds in three of my newly weeded and watered (thanks to the rain) garden beds.
This mix contains annual seeds like crimson clover, annual rye grass and yellow peas, as well as winter rye and hairy vetch that will go dormant but begin growing again in the spring. The annual crops will die and rot in place; the rye and vetch will need to be cut down and then turned under.
Green manures serve several functions. First, they are called cover crops because they cover the soil during the fall and winter seasons and prevent soil erosion by wind or heavy rain.
Second, cover crops suppress weeds by covering the soil so wind borne seeds cannot find a place to germinate. They also help crowd out weeds. This is especially important to me this year because the droughty summer of 2012 was the weediest year I have ever endured
Third, they provide nutrients to the soil. Legumes like hairy vetch, yellow peas and crimson clover fix nitrogen in the soil making it available to the crops that will follow. Non-legumes like rye will add organic matter to the soil. I never have enough compost for my garden so by growing a cover crop I will get the additional organic matter I want. This organic material improves soil structure, helping both sandy and clay soils.
Fourth, the deep roots of cover crops help break up compacted soil and bring nutrients closer to the surface where it can be used by the next crops. .
Fifth and finally, cover crops act as a part of the crop rotation plan. It is always important to rotate crops from season to season, letting light feeders like lettuce follow heavy feeders like squash, and preventing crops from the same family, like potatoes and tomatoes, from following each other because they are susceptible to the same diseases and insects.
That’s a lot of benefit from a $6 packet of mixed seed. Cover crops are an inexpensive way of sustainably maintaining soil fertility and tilth, and keeping down weed growth which will mean less work for me over the course of the season. I have known about the benefits of cover crops, but have never tried to plant them before because of my own misunderstanding.
I did not understand that not all cover crops need to be cut down in the spring. Annual crops are winter killed. Nor did I understand that the young tender growth of winter rye could be cut and turned under with relative ease, and that the tender growth would rot quickly. I envisioned myself digging up, armed only with a spade, great heavy clods of grassy rye that would make planting all but impossible. Now that I have a better understanding of the process I am eagerly trying cover cropping. I might only learn, this first time, what misunderstandings on my part I have not yet uncovered.
I have also just learned about a new cover crop. Tillage radishes. The familiar daikon radish can act as a cover crop when planted in late August. My friend, Rol Hesselbart, has planted one of his wide garden beds with these radishes and the new growth has nearly covered the ground already.
Tillage or forage radishes supply all the benefits of other annual cover crops, but their long fleshy roots rot quickly in the spring and provide an early supply of nitrogen, as well as other nutrients, and a good helping of organic matter. No tilling is needed in that bed in the spring because the radishes have died over the winter. The bed is ready for spring planting without any further work. Sounds like a pretty good deal. I will be watching Hesslebart’s experimental bed to see how it does.
I am not only planting cover crops this fall. Fall is as important a planting season as spring. I will plant my garlic in October and mulch the bed heavily with straw. Garlic will begin to grow again early in the spring and will be harvested in July. That will leave me with a very weed free bed to plant with crops like beets, broccoli, turnips that will ripen before the first hard frost. My garlic did win second prize at the Heath Fair this year.
I also going planted one wide vegetable bed with Rouge de Bordeaux, a winter wheat that will also be ready for harvest in July. I bought my ounce of seed from the Heritage Wheat Conservancy. Thinking of harvesting wheat I am feeling a bit like the little red hen who planted wheat, threshed it, ground it, and then baked it into a beautiful loaf of bread all by herself. I am not nearly as worried about growing or even threshing my wheat as I am about grinding or milling it. I may end up with a very dense loaf of bread. I’ll just call it rustic.
The wheat will also act as a cover crop. It will keep down weeds, and the rotting roots will enrich my soil after the wheat is harvested. I’ll also have a little bundle of straw to use as mulch and, of course, I’ll have my wheat. I love multi-functional plants!
Between the Rows September 1, 2012