Washington State University Extension

Garden Tips


GARDEN TIPS – Written by Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Published August 21, 2016

If you ever hear gardeners talking about green manure you might be wondering just what type of animal produces green manure? It is not produced by an animal. They are talking about cover crops. These are crops planted in the garden and tilled back into the soil primarily for the purpose of adding organic matter, but they also provide additional benefits. These other benefits include the reduction of soil erosion from wind and water, the relief of soil compaction by crop roots, the discouragement of weeds by shading, and decreased nutrient loss over the winter by temporarily tying up of nutrients.

I do not know many area vegetable gardeners who plant cover crops, but they should consider it. Late summer through early fall, mid-August to mid-September is a good time for area gardeners to seed a cover crop in the garden. This is early enough to give them time to grow before cold weather begins and while irrigation water is still available.

There are different types of cover crops that can be used in gardens or on farms, including grains, grasses, legumes, and broadleaf crops, each with different benefits and management techniques. For home gardeners, an important consideration in the selection of a cover crop is how easily it can be worked into the soil next spring. Unlike farmers that utilize cover crops, most home gardeners do not have tillage equipment that makes it easy to incorporate the plant material into the soil.

Home gardeners will want to pick a crop that grows quickly and can be easily worked into the soil. Some cover crops may get too tall to easily work them into the soil without cutting them first. Depending on the crop, gardeners can use a rotary mower (without the mulching attachment), a string trimmer, scythe, or grass whip for cutting the crop down.

If you want to give cover crops a try, you do not need to end your vegetable gardening season early and remove plants that are still producing. Cover crops can be planted between rows or plants. If you have areas of the garden that are finished producing, remove the plants and seed the entire area.

Leguminous cover crops (vetch, clover, beans, peas) are desirable because they add both nitrogen and organic matter to the soil. However, legumes work in association with a special soil bacteria, called Rhizobia, that take or Afix@ nitrogen that is in the air. If you select a leguminous cover crop, you will need to inoculate the seed with the right Rhizobium species for that crop or purchase seed that is pre-inoculated.

When making the decision of what cover crop to grow, consider the advantages and disadvantages of each. For more information on selection consult the WSU Extension factsheet Cover Crops for Home Gardens East of the Cascades FS117E found at In addition, a good resource on the use and management of cover crops in the garden is Methods for Successful Cover Crop Management in Your Home Garden FS119E at

Once you decide what cover crop to plant, ask your local garden or feed stores if they carry the seed. If not, there are on-line sources of cover crop seed including Territorial Seed Company (, High Mowing Organic Seeds (, and Peaceful Valley Farm & Garden Supply (

Garden Tips, WSU Extension, Benton County, 5600-E West Canal Drive, Kennewick, WA 99336-1387, 509-735-3551, Contact Us

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