Green Manures
Any crop grown on land with the intent of turning it into the soil is called a green manure. Generally, legumes and various grasses are grown as green manure. Planting and then tilling or turning under a green manure crop can provide a number of benefits, including increasing organic matter of the soil, decreasing certain disease problems, and increasing the nutrient level in the soil. After the green manure is turned under, it decomposes and adds nutrients and organic matter to the soil.
When used as a green manure, grasses and small grains can decrease the incidence of nematodes. Nematodes are microscopic worms that feed on certain plant roots, weakening the plants.
Using various legume crops can increase the amount of nitrogen in the soil. The amount of nitrogen will depend on the crop, the time of year, and when in the crop cycle the plants are turned under. Anywhere from 30 to 125 pounds of nitrogen may be added to the soil when a legume crop is turned under.
Green Manure Crop Types For Vegetable Gardens:
You can find the seeds for these cover crops at your local Feed & Seed Store, or order them from an online mail-order seed company.
Alfalfa: Alfalfa, a nitrogen fixer, is a suitable cover crop for large gardens or orchards. It requires a full season to mature. Alfalfa roots deeply, so use it to break up hard soils. You can plant alfalfa in the Spring in cold climates, or in the Fall in mild climates.
Clover: Red clover is one of the best for an adaptive cover crop, tolerating shade, acidic soils, and poor drainage. Nitrogen-fixing red clover is low growing, so you can dig it in with a spade rather than a tiller.
Fava Beans: Fava beans not only enrich the soil, they also provide the organic gardener with a crop he can eat at the end of the growing season. Even if you don't like the taste of fava beans, save some seeds for future cover crop sowings. Fava beans act as nitrogen-fixers, and withstand cold temperatures well.
Ryegrass: Ryegrass is an excellent grass that tolerates cold conditions and grows quickly, so you can plant this as an early Spring cover crop before you plant your Summer garden. Make sure you plant the annual variety, not the perennial variety used in lawns.
Winter Vetch: You can plant winter vetch, a nitrogen-fixing crop, in the Fall and till it under in the Spring. This crop can get woody if you allow it to grow too large, so cut it down with a mower as soon as the ground is workable and give it a few days to wilt before you till it into the soil.
Soil Solarization
Difficult-to-control weeds and soilborne pathogens may be controlled with soil solarization. Soil solarization should, however, be reserved for solving these specific problems in your garden because it can also kill beneficial microorganisms and insects.
Soil solarization involves covering the soil surface with clear plastic for four weeks or longer. To begin with, all plant material and crop residue, as is practical, should be removed. The soil should be turned to break up any clods of soil and raked smooth. The area should be watered thoroughly so the soil is saturated. The area then should be covered with a plastic sheet. The sheet can be secured along the edges with soil or rocks. Soil solarization works best when air temperatures are high and sunlight is most intense during the summer months. Soil solarization is not effective during extended periods of cool temperatures or overcast weather.
