Follow rules to use manure

Q. Is there a difference between horse manure and cow manure? Which is better to use on a vegetable garden or on a flower garden? When should the manure be applied?

Ralph from Boardman

A. Animal manures and animal manure-based composts will provide soil with needed plant nutrients such as nitrogen (N), phosphorus (P) and potassium (K), as well as valuable trace elements. In addition, they provide organic matter, which will improve the drainage and aeration in the heavy clay soils found throughout the valley. The organic matter also will improve the water- and plant-nutrient-holding properties of the soil.

Fresh manure should be applied to flower or vegetable beds in the fall. It should be incorporated into the soil and not left on the surface. Decomposition of the soil-dispersed manure for 120 days is normally required before the risk of transmitting human pathogens to edible products is eliminated. Thus, you will need to incorporate fresh manure in the fall.

For spring addition, animal manure should be composted. Proper composting will decrease the volume of the material, eliminate weed seeds and kill harmful pathogens. For more information on manure composting see

Horse and cow manures are probably the easiest to obtain in our valley. Both have similar potential plant nutrient content and may be used in both vegetable and flower gardens. Because horse manure contains considerable wood materials derived from traditional horse bedding, decomposition of fresh horse manure by soil microorganisms will remove large amounts of available nitrogen from the garden soil. The resulting soil may become deficient in available nitrogen for your plants.

Both fresh horse and cow manures contain nitrogen, phosphorus and potassium. However, much of the nitrogen is chemically combined in complex carbon compounds. The nitrogen will be released (mineralized) only after decomposition by soil microorganisms (slow release nitrogen). Although the process begins as soon as the manure is mixed with soil, the nitrogen release can occur over a period of years.

Ultimately, about 1 pound of nitrogen can be obtained from 800 pounds of fresh horse manure or from 650 pounds of fresh cow manure. Similar amounts of fresh manure will provide 2-4 pounds of phosphorus and potassium. If a gardener supplies all of the nitrogen with manure, there is a risk of building up very high levels of soil phosphorus. As always, monitoring garden soil by regular soil testing is recommended. For more information on using manure in your garden see

This week’s answer provided by Bill Snyder, OSU Extension master gardener volunteer. Call the office hotline at 330-533-5538 to submit your questions. Regular clinic hours are over for the growing season, but you can still call and submit questions. Hours vary throughout the winter season.