Leaves fall from trees, plants grow

Gardening is often said to be the most popular leisure pastime in America.

This statistic includes lawn-mowing, which might not fit your definition of gardening — or leisure. But most garden work is healthful outdoor play that gives you delicious food and beautiful surroundings.

Gardening has only one drawback as an American hobby. It doesn’t make anyone money. There is very little you need to buy. There is not even much you need to do. The labor force is plants, bacteria, bees. There isn’t even very much a garden writer can say. If you are paying attention, the world out there is a fully illustrated gardening manual, wide open to the relevant page if you are willing to read it.

Take autumn leaves. Nowhere in Nature’s book does it tell you to burn your leaves or haul them to the dump. In her program, leaves fall from the trees in autumn and accumulate on the ground. Rain and snow flatten them and soil microorganisms break down their carbon and nitrogen to form proteins that plants can use.

Worms and other creatures incorporate leaves into the earth, to create dark, rich woodland soil. If you look at the forest floor you can see layers in gradual stages of decay, with smaller and smaller leaf flakes visible. At the bottom is the rich humus called leaf mold. It’s Nature’s compost pile.

When you make your own compost pile from kitchen and garden wastes you are imitating this process, but in a speeded up fashion. One is usually advised not to add autumn leaves to the pile because they mat down and decompose so slowly. It’s fine to use a few, especially ones that mat less, such as oak, or those that break down faster like alder and willow.

So what should you do with the rest? If there aren’t too many, you can just let them sit there and gradually break down, or blow to the edges of the yard. In fact I have often raked mine into shrub or tree plantings as a mulch.

If there are lots, you have the marvelous opportunity of putting them into their own separate pile and making leaf mold, as a soil amendment for the garden. For those of you who like recipes, it is a simple one: make a pile and wait three years. Unlike the moister, high-nitrogen wastes in a normal compost pile, which need air to activate the bacteria that break them down, autumn leaves are broken down chiefly by fungi, who work in airless conditions.

Any kind of leaves can go on the pile, with the exception of black walnut which contain a substance toxic to other plants. Evergreen needles tend to be very acid and slow to break down. Leaves from deep rooted trees such as oaks are best, because they bring up minerals such as boron, iron and manganese, from far below. Neighbors are often happy to let you rake up their leaves, but avoid roadsides, where poisons accumulate.

Leaves will decompose better if you enclose them within a circle or rectangle of wire mesh, snow fence or some other handy material, at least 4 feet across. Simple metal stakes can support it. A shallow pit with mounded sides also works.

Many people think they have to buy a large, noisy, expensive, gasoline-powered shredder to chop up the leaves first, but this isn’t necessary. If you have a mulching lawn mower you can mow over the leaves a few times, to speed up the process. But they also compost who only stand and wait.

I like a system where you have three piles: one in which you put your leaves this fall, one from last year that just sits, and one with finished leaf mold you can use during the next growing season. You also can just build one perpetual pile from which you dig finished leaf mold out of the bottom as needed.

So what do you do with this wonderful stuff? The traditional use for leaf mold was as an ingredient in potting soil, before everyone had access to peat. This is still a good use for fine textured leaf mold, which has more nutrients than peat does, and just as much moisture-holding capacity. I also would add it to any bed that needs an extra kick. Try forking it into the soil this fall, to prepare for a brassica crop next spring. It is the ultimate slow release fertilizer and a good insurance policy if you’re not sure your soil has all the trace elements it needs.

Even moderately well-rotted leaves will lighten your soil, make it more moisture-retentive and help give it that magical sponginess you feel underfoot when you walk in the forest. It’s such a simple formula, really. Leaves fall from trees. Plants grow.

Barbara Damrosch

Barbara Damrosch

Barbara Damrosch’s latest book is “The Four Season Gardener’s Cookbook.”
Barbara Damrosch

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