Green manures are crops planted on the soil surface that enhance soil fertility and texture.
Buckwheat is a fast-growing, warm-season, succulent, broad-leafed annual plant, that can smother out weeds, protect the soil surface and provide habitat for pollinating and other beneficial insects.
With a fibrous root system, buckwheat seed can germinate within days of planting, especially if the soil is warmer than 55 degrees. Not requiring much water and tolerating poor fertility, buckwheat is ideal for many less-than-ideal places in your garden. But be forewarned – it does not like saturated soils or shade.
Since buckwheat is a succulent, it decomposes rapidly, and does not provide much organic matter to the soil. But it does improve the short-term tilth of the soil, and better prepares your garden bed for transplants. It is particularly efficient at taking up phosphorus from the soil and storing it in its tissues. There is some research evidence that incorporating buckwheat residues can increase phosphorus availability to the subsequent crop.
Because it grows so fast, buckwheat is ideal for planting in places that might be left otherwise bare over the summer, such as spare garden beds whose spring crops are harvested and fall crops are yet to be planted.
"Sometimes home gardeners get overly ambitious with a rototiller in the spring," said McGrath. "If you work up too much ground, then the ground that you don't plant can get away from you and become a mess of difficult to control weeds. My advice to the gardener who has 'bitten off more than you can chew' is to plant buckwheat to hold the tilled area until you have time to plant new crops."
Buckwheat reaches flowering stage at about two to four feet high, in as little as four to five weeks. It continues to flower for several weeks, then sets seed two to three weeks after flowering. Buckwheat seeds are eaten by ground dwelling birds including pheasant and quail.
Buckwheat can become a weed under certain circumstances, said McGrath. "But, I consider buckwheat to be a 'good weed' because it is relatively easy to kill and it crowds out other weeds that are much more difficult to kill."
Farmers kill it with herbicides, mechanical cultivation and mulching. Home gardeners can easily pull it out or chop it down before it sets seed. Since buckwheat is frost sensitive, it will winter kill naturally. Buckwheat seeds can survive over winter in many parts of Oregon.
Plant buckwheat in the spring to early summer. Scatter the seed over your garden bed, at a rate of about one pound per 500 square feet of garden space (about three ounces per 100 square feet) and rake and water in. Though plants may appear wilted on hot summer afternoons, buckwheat does not require much water.
Mow or cut down buckwheat within 2 weeks of first flowering if you want to avoid setting seed that could cause a "weed" problem in your following crop. Turn the buckwheat plants into the soil. They will decompose rapidly and not hinder your planting of subsequent crops.
Some examples of a use of buckwheat in the home garden as a cover crop might include:
After harvest of late spring lettuce, plant buckwheat in early June. Then, in late July till it under and plant broccoli starts for over wintering.
After picking all your overwintered cole crops in May, plant buckwheat, then plow under after flowering in July or August. Then plant leafy salad greens or overwintering carrots or onions.
In a particularly weedy area, cut back and till under weeds in the spring or early summer and plant buckwheat, which will smother out the weeds. Then plant a fall-planted crop such as garlic.
If you want to grow buckwheat for seed or grain, it will take about three months from time of planting.