If you have deciduous trees in your garden, you might be fretting these days over the task of raking and disposing of the fallen leaves.
You might instead welcome this form of nature's bounty, because your trees have contributed the raw material for an excellent natural resource for your garden: leaf mold.
Leaf mold, which is simply partially decomposed leaves, can be used as a mulch to discourage weeds, retain moisture and insulate the roots of plants from the coldest weather. It can also be used as a pH-neutral soil amendment, like compost, to retain moisture, improve soil texture, add nutrients and support the growth of beneficial soil organisms of all kinds.
The question, then, is how to convert the fallen leaves to lead mold?
The raking can't be avoided, but the rest of the task could take any of several forms, depending on the gardener's patience and available space, and the kind of leaves. Some leaves, including oak and holly, contain relatively high levels of cellulose and are slower to break down.
The easiest conversion of leaves to leaf mold is to pile the leaves in an out-of-the-way location and let them decompose on their own schedule. This process could require a year or more, but could be hastened in several ways, singly or in combinations.
Leave your leaf pile in a shaded location, or cover it with a plastic tarp. This helps to retain moisture, which supports the decomposition process, which depends upon the work of fungi.
Water the leaf pile occasionally, to maintain a damp (not soggy) condition.
Turn the pile occasionally, to expose the contents to oxygen.
Shred the leaves. Smaller pieces have greater exposure to the air and moisture, and therefore break down faster. Run over the leaves with a lawn mower — almost any kind would do — or put them through an electric leaf shredder or leaf blower-vacuum.
My American Sycamore's big leaves tend to block my blower-vacuum, so they have to be roughly shredded first with the mower. For smaller quantities, place the leaves in a trash can and shred them with a Weed Whacker.
Add nitrogen. Old dry leaves are almost all carbon, so the addition of nitrogen will speed their breakdown. Add green vegetation or nitrogen-rich fertilizer. Dry chicken manure has twice the nitrogen content as horse or steer manure.
The leaf mold is ready when it has become soft and crumbly. Use it to mulch your plants, spreading it about 3 inches deep (not too close to the base of the plant). Or dig a similar amount into the soil; this could be easiest when preparing a new bed, and is particularly helpful for improving soil that contains an excess of clay or sand. Leaf mold also could be included in containers to lighten their weight.
Enjoy gardener's gold in your garden.
Tom Karwin is a Santa Cruz resident, a UC Master Gardener, a member of several garden groups, and vice president of the UCSC Arboretum Associates. Contact him at firstname.lastname@example.org.