Fallen leaves contain up to 80 percent of the nutrients that a tree absorbs during the growing season. When allowed to decay on the ground, leaves return their store of nutrients to the soil, where they’re reabsorbed by the roots and channeled back to a new season of growth.
Leaves can also serve as a key component of your garden’s soil. If you don’t use the annual bounty of leaves, you miss the opportunity to add a rich, natural source of organic matter to your garden. Unless organic matter is replaced with regular applications of compost, mulch, and other imported matter, the humus-deprived soil loses its ability to retain moisture and nutrients. It becomes less hospitable to microorganisms, and the pH levels drift out of balance.
As nature’s perfect mulch, fallen leaves are a favorite food of earthworms everywhere. A thick layer of leaves can turn a patch of ground into an earthworm factory, enriching the soil with one of the natural world’s finest-quality fertilizers—worm castings.
Here’s how to get the most from your leaves:
Shred the big guys. Large, leathery leaves such as oak can take years to break down. Left in thick layers, they become barriers between rainfall and the soil, turning garden beds into drought zones. Leaf vacuums/shredders can reduce a mountain of leaves to one-sixth of its volume. Or you can use a lawn mower to shred dry leaves in place, either spewing them toward beds or collecting them in bags.
Use them as summer mulch. Place a thin layer of shredded leaves in direct contact with the soil so that microorganisms can turn them into dark, fungi-rich leaf mold. Thin layers of leaves will keep the ground cool, hold in moisture, and stifle weeds. Though fresh leaves are high in carbon and low in nitrogen, they won’t draw nitrogen from the soil during decomposition unless they are turned under the surface (not recommended).
Use them as winter mulch. Shredded leaves make attractive mulch. Piled around garden plants after the ground freezes, they provide protection for tender plant roots while allowing winter moisture to reach the ground.
Use them as a soil amendment. Mix partially decomposed leaves into the soil to provide aeration while improving nutrient and moisture-holding capacity. Over time, leaf humus tends to moderate soil that’s too acidic—except large quantities of highly acidic oak leaves that can have the opposite effect. Apply leaves to your garden beds in the fall after plants are dormant, along with a nitrogen source such as fish emulsion. Caution: Don’t use leaves from diseased plants. Also avoid black-walnut leaves, which contain a toxin that can retard the growth
of garden plants.
To compost your leaves instead of applying them directly to the garden, follow these tips:
• Shred or crush leaves. This reduces the decomposition time by at least 25 percent. (Make sure leaves are fairly dry, not damp, to avoid clogging your shredder or lawn mower.)
• Mix with high-nitrogen green matter. The proper ratio is one part green (nitrogen-rich) matter, such as grass clippings that have not been treated with a herbicide, to two parts dry leaves (carbon-rich). Save bags of leaves to mix with fresh grass clippings next summer.
• Keep the pile moist. Add water to keep the pile as damp as a squeezed-out sponge.
• Provide plenty of air. Turn the pile once a month.