AMES, Iowa — The rustle of leaves underfoot, children playing in piles of leaves and the blending of bright leaf colors are the positive aspects of lawns covered in leaves during autumn. However, homeowners must decide when and how to remove fallen leaves before the Iowa winter freezes them in place. Iowa State University Extension and Outreach horticulturists respond to questions about removing and using autumn leaves. To have additional questions answered, contact Hortline at hortline@iastate.edu or 515-294-3108.

Do I need to remove the leaves on my lawn?

Turfgrass plants utilize light, water and nutrients to manufacture food. In fall, lawn areas beneath large trees are often completely covered with leaves. The leaf debris prevents the turfgrass plants from manufacturing and storing food prior to winter. Additionally, the leaves of some tree species mat down readily and may smother the grass. Thick layers of leaves should be raked up and removed. Small amounts of leaf material can be chopped up with a mulching mower and left on the lawn. Make sure the leaves are chopped small enough to fall through the turfgrass canopy. This may require going over the lawn two or three times with the mower.

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 it will decompose.

Construct the compost pile in layers. Each 6- to 8-inch layer of plant material should be topped with 1 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 3 to 5 feet high.

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

Are leaves a good winter mulch?

Winter mulches aren’t necessary for most plants in the garden. However, winter mulches help ensure the survival of strawberries and a small number of perennials over winter.

Winter mulches are applied in late fall to protect plants from extremely cold temperatures. They are also applied to prevent repeated freezing and thawing of the soil that may heave shallow-rooted plants out of the ground and severely damage or destroy the plants.

Leaves are generally not a good winter mulch as they tend to mat down. The matted leaves don’t provide much protection and may actually damage plants due to excess moisture trapped under the material.

The best winter mulches are materials that remain loose and airy through the winter months, such as straw and pine needles.

— Richard Jauron and Willy Klein, Iowa State University Extension and Outreach

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