Nutrient-rich leaves can help compost piles

Posted Sept. 24, 2010, at 7:13 p.m.

I can think of a couple of good reasons to rake autumn leaves into huge piles. Neither involves stuffing them into plastic bags to be left at curbside until trash day.

Most important is a child’s need to jump headfirst from a running start into the pile, to hide perfectly still below the surface, breathing in the pungent organic odor, until routed out by a dog’s cold nose. I am too old to fly into the pile as Lynne would do when she was just a few years younger — and might do even now if none of her high school friends are around, but I can remember being 10 years old on blue-sky October afternoons, my father heaping up the leaves after every flying leap. And I will still wrestle in the leaves with our dogs; it just takes longer to get upright again.

And I would rake leaves to recycle their nutrients into leaf mold and compost for the garden. True, much of what leaves contain at the end of their life is reallocated to more permanent parts of the plant. But those dry, brown remnants of summer have a surprisingly high nutrient element analysis. Fallen leaves of deciduous trees such as maple, beech, ash, and oak contain about 0.5 percent nitrogen, 0.1 percent phosphorus, and 0.5 percent potassium, along with equally substantial amounts of calcium and magnesium, all essential nutrients for plant growth.

Because decomposition of leaves is a slow process, these nutrients are released gradually — nature’s version of a slow-release fertilizer. Indeed, annual topdressing with decomposing leaves (called leaf mold) is all the fertilizer that trees, shrubs and many perennials need for healthy growth. Even lawns are healthier for the nutrients released from fallen leaves by a mulching lawn mower.

Nutrients, however, are only part of the garden worth of autumn leaves; leaf mold also improves both the structure and water holding capacity of the soil. While rich topsoil can hold 60 percent of its weight in water (compared to 20 percent for subsoil), leaf mold can retain 300 percent of its weight, or more.

The question then becomes not what to do with autumn leaves, but how to do it, how to make leaf mold? Start by shredding the leaves into small pieces that will break down quickly. This can be done with special grinders designed for the task or with a lawn mower. (I found one Internet source that actually recommended using a weed-eater to shred leaves in a trash can!) The resulting mulch can be immediately spread in the garden walkways to control weeds and around your trees and shrubs as well.

Some of the shredded leaves can be added to the compost pile, but only sparingly unless they are mixed with high-nitrogen materials such as grass clippings or stable manure. Too many leaves and the composting process stalls, while a mixture of five parts leaves to one part manure will decompose quickly.

Reluctant to rob nutrients from the woodland garden, we rely on a willing neighbor with an endless supply of autumn leaves. We wait for a blue-sky Saturday afternoon to walk down the road, rakes in hand, to make the piles. In the past, we would build them tall and broad for Lynne and Reilly, and when we were all tired of the play we hauled the leaves home, building another pile beside the shredder.

Now it is all work. The dogs still get excited, try to get someone to jump in the piles, but no takers. We haul the leaves home, scatter them over the drain field, and then run them over with the mower with the grass-catcher attached.

Later, driving into town, we see piles of black plastic bags at the side of the road, bulging with leaves that will decompose long before the plastic rots, leaves that will never release their nutrients to nourish new life in a garden. We both say what we are thinking, that it is a crime.

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