Leaves are one of nature’s great nutrient recyclers. Throughout the growing season, they are food factories for trees and shrubs, turning sunlight and water into sugar. Then, as nighttime temperatures cool and the days shorten, the factories shut down and fall to the ground. In doing so, they return a wealth of accumulated nutrients back to the soil.
In forest ecology, fallen leaves support entire ecosystems as they break down. Fungi have the primary responsibility for decomposing the tough cell walls, followed by earthworms and other terrestrial invertebrates that devour the fungi. Ultimately the leaf remains become part of the rich, dark, sweet-smelling earth that goes on to support future generations of plants and animals.
In our yards, leaves are every bit as useful. Plus, we have the ability to influence the decomposition process by moving, storing, shredding, and incorporating them with other compost ingredients. Following are some of the best ways to use fall leaves in your composting system.
One of the easiest ways to collect leaves, shred them, and start a compost pile, is to pick them up with a bagging lawn mower. The mower grinds up the carbon-rich leaves along with high-nitrogen grass clippings, making an excellent compost blend.
Empty the collection bag into a compact pile, and add enough water to thoroughly wet the mixture throughout. Continue building the pile until it’s about 4-feet tall, 4-feet wide, and 4-feet long, then cover it with a tarp to hold in the moisture and block out sunlight. Turn the pile once a week, and the batch will be ready to use within two months.
In traditional composting systems, the ingredients are categorized as either nitrogen-rich “greens” or high-carbon “browns.” Bacteria and other composting microbes need a 4-1 ratio of browns to greens to process the material efficiently.
Early in the season, autumn leaves offer a fair amount of nitrogen, but as the season progresses and the leaves dry out, they quickly become a primary carbon source. When adding fallen leaves to this type of system, consider them as you would other browns.
In many areas, leaves continue to fall well after grass stops growing. This is a perfect time to make leaf mold. Leaf mold is a “cold compost” made of nothing but fallen leaves. Because it relies on fungi to colonize and break down the leaves, it can take a year or more to finish a batch, but making leaf mold requires no labor beyond building the initial pile.
In a shady location, use T-posts and fence wire to build a 4-foot high, circular bin with a diameter of at least four feet. Line the bin walls with plastic to minimize moisture loss, leaving the bottom open. Fill the bin with fallen leaves, wetting them as you go. Open the bin in a year or two to collect the leaf mold.
Worm composting, or vermicomposting, is a way to make compost quickly in a confined space. These systems start with worms and some sort of carbon-rich bedding, to which kitchen scraps and other high-nitrogen material is added in small quantities over time. The bedding material captures excess moisture and nutrients, provides shelter for the worms, and keeps the texture of the compost much more open.
To start a worm composting bin, fill a 10 gallon plastic tote about three-quarters full of shredded leaves. Wet the leaves well—they should feel like a gently wrung-out sponge. Add worms to the bin and feed them weekly with finely chopped kitchen scraps. The worms will consume about three times their own weight in food waste each week. Add fresh bedding as needed. When the bin is about halfway full of compost, with just a thin layer of bedding at the top, harvest the compost and start a new batch.
Composting isn’t necessary before using fallen leaves for mulch, although shredding is recommended. The leaves slowly decompose throughout the winter and spring, feeding the soil-dwelling microbes and plants as they help to protect and improve the soil.
Mow leaves directly into the lawn with a mulching lawn mower, or collect shredded leaves to use around veggies, herbs, flowers, and landscape plantings. Apply thin layers of leaf mulch, no greater than two inches thick. Thicker layers will soak up rainwater to the detriment of the plants beneath.
Another good way to enjoy the benefits of fallen leaves is to pile them on a dormant garden bed. As they cover the bed through winter, they insulate the soil from wide temperature fluctuations, allowing biological action to continue. Fungi continue to decompose the leaves that are in close contact with the soil, and worms travel between the leaf pile and lower soil layers to incorporate the material.
If you’re not using autumn leaves in your lawn care regimen, it’s time to reconsider your habits. Fall leaves are some of the best raw materials for composting. They provide a rich source of carbon for decomposers, and add significant quantities of trace minerals and plant nutrients to the mix. Leaf compost is one of the best soil amendments that money can’t buy.
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