Autumn Leaves - A Valuable Soil Conditioner

Diane Turner, Conservation Technician and Outreach Assistant

Autumn leaves don’t have to become trash. On the contrary, they easily can be turned into valuable soil-enhancing organic matter. For many urban dwellers, who already have their yard waste picked up by the city, this service is likely to continue. Many communities compost their leaves and make the finished compost available to their citizens. Compost improves soil aeration, moisture retention and drainage, and nutrient-holding capabilities.

For those who do not have the luxury of yard waste pick up, there are several ways to manage tree leaves at home. Green-thumbed gardeners long have known the value of recycling plant material. Dry leaves can be plowed or tilled under in the vegetable or annual flower bed in fall to provide a source of organic matter. Shredding the leaves first will speed the breakdown so that the leaves will not be visible by spring. Be sure to mix the leaves into the soil, rather than leaving them on top through the winter, to avoid keeping the soil too cold and wet to work in the spring.

Tree leaves can be recycled directly on the lawn. Use your mulching mower or shredder/vacuum to break dry leaves up into smaller pieces. A mulching blade will speed this process, but even a standard blade will do an adequate job. For large leaves like maple and sycamore, it may take several passes to get a finely shredded product. Once the leaves are pulverized, they will break down quickly. A fall application of nitrogen fertilizer (about 1 pound of nitrogen per 1,000 square feet) will help speed decomposition of the leaves and also will benefit the grass plants.

Fall leaves also make great composting ingredients, especially when mixed with green trimmings and grass clippings. Again, the smaller the pieces, the faster they’ll break down, so shred or chop dry leaves before adding them to the compost pile. If you don’t have green trimmings or grass clippings, add a source of nitrogen to the leaves, such as dry cow, horse, sheep, or poultry manure. The nitrogen is needed by the microorganisms that break down the carbon in plant materials. Add a sprinkling of soil or finished compost to introduce a source of the microorganisms, and water just enough to moisten. The compost will heat up in the center as it breaks down. Stir the contents occasionally to add air and allow for uniform heating. Generally, the more often you turn the pile, the faster you’ll get a finished product. Compost is ready to add back into the garden when it looks uniformly dark and crumbly.
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Last, but not least, shredded leaves can be used as a winter mulch to protect tender perennials through the coming harsh weather. Shredding the leaves will help prevent them from packing down as they get wet and smothering the plants that they are supposed to protect. To provide winter protection, apply a 3-6 inch layer of shredded leaves over the top of tender perennials after several hard freezes. The goal of winter mulch is to keep plants dormant through the winter, so it must be applied after the ground is cold and plants are fully dormant. The timing of application will vary from year to year with the weather, but generally will be appropriate sometime between the Thanksgiving and Christmas holidays.
Excerpts taken from the Much Ado About Leaves by Rosie Lerner, Purdue Consumer Horticulture Program.  

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