December 5, 2011

Yard and Garden: Fallen Leaves

By Richard Jauron and Willy Klein
Iowa State University Extension Scott County

Composting enables gardeners to dispose of large quantities of leaves and clippings in an efficient and cost-effective way. Iowa State University Extension horticulturists share ways to use fallen tree leaves. Gardeners with additional questions should contact the ISU Extension Hortline at or call (515) 294-3108.

Can oak leaves be used as a garden mulch?

Yes. While oak leaves are slightly acidic, an oak leaf mulch should have little effect on the soil pH. Shredded leaves are an excellent mulch for vegetable gardens, raspberry plantings, perennial flower beds and around trees and shrubs. Oak leaves can be shredded with a lawn mower or a leaf shredder.

What is the nutrient content of composted leaves?

The nutrient content of composted leaves is very small. The levels of nutrients vary somewhat from species to species. However, the nitrogen content of composted leaves on a dry basis usually varies from 0.5 to 1.0 percent. Potash amounts are in the same range. Phosphate amounts are around 0.1 percent. Increasing the organic matter content of the soil is the main benefit of incorporating composted leaves into the soil.

How can I accelerate the decomposition of leaves in my compost pile?

Leaves contain high levels of carbon and small amounts of nitrogen. The microbes that decompose leaves and other types of organic matter require nitrogen for their own metabolism and growth. A compost pile composed mainly of leaves decomposes slowly because the leaves don’t contain adequate levels of nitrogen for the microbes.

To promote decomposition, mix leaves with grass clippings or other materials high in nitrogen. If possible, shred the leaves prior to composting. The smaller the size of the material, the faster the rate of decomposition.

Construct the compost pile in layers. Each six to eight inch layer of plant material should be topped with one inch of soil or compost. A small amount of an all-purpose garden fertilizer, such as 10-10-10, can also be added to supply nitrogen to the microbes. Continue to build the compost pile in layers until it is three to five feet high.

Finally, water the pile regularly and turn it about once every two weeks.

Are leaves a good winter mulch?

Winter mulches are applied to plants, such as strawberries and chrysanthemums, in fall to prevent damage caused by extreme cold or repeated freezing and thawing of the soil during the winter months. Leaves are a poor winter mulch for strawberries and herbaceous perennials. Leaves tend to mat down and don’t provide much protection. Clean, weed-free straw and pine needles are excellent winter mulches. Straw and pine needles don’t mat down, provide good winter protection and are easy to remove in spring.