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Leave the Leaves

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Submitted By Bill Seldon:

It´s the time of year again when leaves begin to fall. Especially with the recent rainstorms, leaves and pine needles are down everywhere. This seems to bring an overwhelming desire for a lot of people to get out and rake their leaves. In some cases this is needed, but in many cases the piles—which end up on the streets—are there unnecessarily.

The leaves which fall to the ground along with twigs, bark and numerous other organisms form a layer on the soil surface. This organic layer is very active biologically and is slowly broken down and decomposed.

This same organic layer is involved in a process known as nutrient cycling. Nutrient cycling is especially important in natural environments, which is what our area was before development took place.

As plants grow, their roots absorb nutrient materials from the soil. The plants use these nutrients to produce wood, bark, roots and leaves. As seasons pass, some plant parts die and are returned to the soil surface where they gradually decompose and nutrients are released into the plants.

This organic layer is extremely conducive to plant growth because it is well aerated and high in nutrients. Previous Master Gardener columns have explained that plant materials contain high levels of nitrogen. When fallen plant materials are broken down by fungi and other microorganisms, the nitrogen can be used by new plants for growth.

Ground which has had the organic layer removed suffers from nutritional losses and becomes more susceptible to erosion from wind and, especially, water. Water erosion is a serious concern in areas such as ours where much of the ground is on slopes.

The organic layer, if left on:

–Helps keep surface temperatures lower than they would be on bare soil.

–Helps conserve ground moisture. (A layer of leaf mulch can reduce your outdoor water needs by half in the summer.)

–Acts as a mulch to suppress the growth of numerous weeds.

I would not suggest people begin piling brush in their yards. After all, fire is a very serious concern in our community. I would simply like people to stop and think. Just because your neighbor rakes his or her leaves does not mean you need to rake yours.


In addition to “leaving the leaves” to break down into a nutrient layer on the ground, leaves can be composted to break down faster. Composting is simple…compost “happens.” However, a little manipulation will accelerate the process, giving you a valuable soil amendment in as little as two weeks.

Leaves can be chopped—smaller pieces break down faster. Layer them—in a pile, a wire cylinder or constructed compost bin—with green kitchen scraps, lawn clippings, and old garden plants, in roughly equal volumes of “green,” nitrogen-containing materials (kitchen scraps and grass clippings) and “brown,” carbon-containing materials (dead leaves). Don´t stress over whether the ratio is correct, or whether you have enough “browns” or “greens.” Composting happens naturally.

Turning compost will accelerate its decomposition. A compost pile turned every day will be ready for garden use in about two weeks. Once again though, don´t stress over turning the compost pile. Even if left completely undisturbed—as on a wilderness forest floor—eventually your leaves will become compost, revitalizing the soil from which they came.

Be sure to add moisture to your leaf compost. Too little water, especially on dry leaves, will prevent decomposition. Too much water fills up the air spaces, depriving aerobic microorganisms of oxygen, and causing the compost pile to form ammonia and methane—which smells bad! When you touch the compost, it should feel slightly damp, similar to the amount of moisture remaining in a squeezed-out sponge.

Drop Off/Pick Up

There´s one philosophy in gardening that pretty much sums up what we´ve been talking about today—“Nothing leaves the property.” When we use the leaves, tree debris, garden plants, and kitchen green scraps on-site, the resulting compost replenishes and nourishes the soil that nourishes our plants and us.

Many of you participated in yard slash reduction or “fire-safe” landscaping this spring and summer in order to reduce the danger of fire in your immediate environment. You may have dropped off your material at a local slash site. Much of this material was chipped and sold to local biomass power generators to create electricity. However, leftover material is too fine to burn, and in fact, is not flammable. This finely ground, sifted material can be used as mulch or compost. Next year when you drop off your yard prunings at a local slash site, consider investigating whether you can pick up a load of fine mulch to take back to your yard and garden to feed the soil.

For more information, contact the City of Sonora Community Development Department at 532-3508 or the Master Gardener program at 533-5696.

See you in the garden.

Bill Seldon is a certified arborist for the City of Sonora and previously authored another column in the Union Democrat on “leaving the leaves.”