Can you compost fall leaves? Here’s what to know

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Fallen leaves are a gift to gardeners that should never be disposed of in the landfill. They make excellent compost, leaf mold, and mulch that enriches soil and boosts plant health. But not all leaves are equal. 

The best leaves for composting, including ash, maple, poplar, willow, and fruit trees, are those that have thin cell walls and contain higher levels of nitrogen and calcium. Leaves with tougher cell walls and low nitrogen content, including beech, holly, and oak, resist the composting process and may be best for other uses such as mulch or leaf mold. Walnut and eucalyptus leaves contain compounds that are detrimental to other plants. These are best used to mulch the trees they came from.

Shred fallen leaves first

For all of their benefits, leaves present a few challenges. They blow around in the slightest breeze, making the yard look untidy. They easily become matted when wet, sometimes to the point of repelling rainwater. They take up tons of space, whether piled up or in bags, as they await usage. Whatever you plan to do with your fallen leaves, it is easier if you shred them. Shredding fallen leaves reduces matting, increases surface area for faster composting, reduces blowing in the wind, minimizes needed storage space, and generally improves handling.

Make leaf compost

Efficient composting requires a carbon to nitrogen ratio of between 25 and 40 parts carbon to one part nitrogen. Too much nitrogen leads to a stinky, slimy mess. Too much carbon and the pile will be extremely resistant to decay. At the ideal ratio of 30:1, the compost heats up quickly as beneficial microbes break down the material. The heat kills off plant diseases and weed seeds. The resulting compost is dark, crumbly, nutrient rich and teeming with beneficial bacteria that garden plants love.

Most gardeners find high nitrogen “green” ingredients easily: Kitchen vegetable scraps, coffee grounds, garden weeds, grass clippings, last season’s annual flowers, etc. Finding carbon-rich ingredients can be more challenging. Many gardeners resort to buying straw or using shredded paper and cardboard; however, shredded autumn leaves make a perfect high-carbon ingredient because they are natural, plentiful, contain beneficial nutrients, and best of all they’re free! 

Start a new compost pile by spreading a 6-inch layer of shredded leaves, 3-feet square. Moisten them thoroughly. Next add a 2-inch layer of nitrogen-rich “green” material. Cover the green layer with a 4- inch layer of shredded leaves, and moisten. Continue alternating 2-inch layers of green material with 4-inch layers of shredded leaves until the pile is about 3-feet tall. The pile can be built all at once or gradually over time. Be sure to cover each new green layer with a layer of shredded leaves. 

Turn the pile every one to two weeks to improve aeration. The pile should always have the approximate moisture content of a wrung-out sponge. Add water as needed. Cover the pile loosely with a tarp to retain heat and moisture.

If you use an enclosed composting system, like a compost tumbler, layering may not be possible. Instead, start with three to four parts (by volume) shredded leaves to one part nitrogen rich material. For each additional part of green material, add two parts shredded leaves. Add water as needed. Rotate the tumbler once or twice a week, and monitor the moisture content.

pile of fall leaves
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Make leaf mold

Leaf mold is the dark, rich, crumbly material that forms on the forest floor. It has an incredible ability to improve soil water-holding capacity, drainage, and nutrient retention. The difference between compost and leaf mold is in the organisms that make it. While composting is performed primarily by bacteria in a warm or hot environment, leaf mold is made by fungi in a cool environment. Bacteria require higher levels of nitrogen, but the fungi that form leaf mold survive on carbon-rich leaves alone. 

The easiest way to make leaf mold is to replicate nature. Simply pile moist, shredded leaves in out of the way part of the garden or yard, and leave them alone for six to 12 months. Several small piles, 3 to 5 feet tall and wide, are easier to maintain than a single large pile. To keep leaf piles intact, use wire or nylon fence to enclose them in cages. A flat top will promote absorption of rainwater. You can expedite the process by enclosing the pile beneath a tarp to retain consistent moisture. 

Use fallen leaves as mulch

If you have no space, time, or desire to maintain a compost pile or leaf mold bin, or if you simply have too many leaves to compost, you can take advantage of natural decomposition of leaves by using them for mulch. Spread a six to 12 inch layer of shredded leaves around landscape plants and over garden beds. Biological activity will remain steady at the soil surface beneath this mulch layer, and decomposers will gradually turn the leaves into humus. Subsoil organisms, like earthworms, then transport the material to plant root zones. 

Eliminate the time and expense of dumping those fall leaves. Instead, turn them into valuable compost for the benefit of soil and plant health in your garden and landscape.

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