Basic Leaf Mold

Instead of carting leaves to the curb, recycle them the way nature does, by turning them into an invaluable soil builder. Leaf mold greatly improves the structure and water-holding capacity of soil. It also creates the perfect conditions for the community of beneficial organisms that dwell in your soil, and it's great in potting mix.

There's really no excuse not to make leaf mold. It's free, easy-to-make, and readily available. If you don't have enough leaves in your own yard, trade raking duty with your neighbors in exchange for theirs. Before you use leaves that have fallen on your neighbors' lawns, be sure to ask them if the grass has recently been sprayed with synthetic chemicals. If so, don't use the leaves. Grass clippings with chemical residues can get mixed in with the leaves and contaminate them, says William Brinton, Ph.D., director of the Woods End Research Laboratory, in Maine. Still, Dr. Brinton explains, chemical contamination is not a significant concern with leaf mold because its lengthy decomposition time allows for chemicals to break down as well. Do not use leaves that have been raked into the street for municipal pickup, because they may contain lots of sand, fuel, or oil residues.

Do-It-Yourself Leaf Mold
Making leaf mold couldn't be easier. Start by ensuring that the leaves are thoroughly moistened, says Abigail Maynard, Ph.D., of the Connecticut Agriculture Experiment Station. Dehydrated leaves begin to lose nitrogen, and this hinders the decomposition process. Here are two ways to transform leaves into leaf mold.

• The lazy gardener. Pile leaves in a sheltered, inconspicuous area of your yard and leave them for two years.
• The ambitious gardener. Make a 3-by-3-foot leaf mold "cage" from stakes and chicken wire. Speed up the leaves' rate of decomposition by running a lawn mower over the pile a few times. To ensure even decomposition, Dr. Maynard suggests, turn the pile occasionally.

Using Leaf Mold
Now, here's how to use this nutrient-rich soil conditioner.

• Peat substitute. Use leaf mold in place of peat because it has similar qualities and it's a renewable resource.
• Moisture-retaining mulch. Leaf mold can hold up to 500 times its own weight in water. Place it around (but not touching) the crowns of annuals, perennials, and vegetables to help them maintain moisture during summer.
• Soil conditioner. It's easier for roots to penetrate soil and take up nutrients when the soil is not as dense. Dr. Maynard and her colleagues in Connecticut completed a 12-year study on the role leaf mold plays in changing soil characteristics. They found that garden soil amended with leaf mold had a 20 percent lower bulk density than soil to which leaf mold was not added.
• Drought-proof soil. The Connecticut study also found that soils amended with leaf mold increased their water-holding capacity by almost 50 percent. The amended soil could hold nearly a two-week supply of water for vegetables. Caution: This water-holding capacity can be a problem for seeds planted in early spring, because they may rot in the cool, wet soil. Dr. Maynard suggests planting extra seeds to compensate for seeds lost to rot.
• Seedling mix. Mix one part leaf mold with one part well-aged compost or worm castings for a nutrient-rich potting mixture for seedlings.

What Is It?
Leaf mold: Leaves that have fully decomposed over a long time.

Leaf compost: Compost made by mixing leaves with other organic materials.

Humus: The dark, spongy material created when microorganisms break down organic matter. Leaf mold and leaf compost both eventually turn into humus.