Leaves are the most abundant and easily accessible material for the compost pile. One of gardening’s enduring misconceptions is that leaves such as maple and oak are acidic. Leaves that have gone through the composting process and come out as leaf mold test close to a neutral (pH) of seven (pH refers to the sweetness or acidity of a soil). In fact, no matter what kind of tree foliage, including pine needles, the final product will have a pH of between six and seven. That’s almost perfect for most plants. Blueberries love acid soils—about a pH of five vs. most vegetable plants which need a pH closer to six or seven. Lime and/or wood ashes increase the pH in your soil.
Leaves are a triple treat for the garden as an addition to the compost pile, as mulch, or as a special organic amendment called leaf mold. They’re a nitrogen source when the leaves are green and a carbon source when the leaves are brown and dry. The problem is that some leaves mat down when wet, which means if they are placed in the compost pile, they’ll pack down and exclude air from the mix and shed water off the pile. Flat leaves such as sugar maples tend to mat together and curly ones such as oaks and silver maples are an airier choice, but they all mat down to some extent when wet.
The best way of dealing with leaves is to shred them with a lawn mower or leaf blower. Or pile them up and let them sit for a few years, turning the pile now and then. This follows the Woodchuck principle of “Leaf It Alone.” Eventually, the leaves will break down into leaf mold, which means they have decayed into rich crumbs. It’s not that they’re filled with lots of fungus and mold even though there’s always a mixture of bacteria and a little mold with the breakdown of most organic materials. Leaf mold occurs naturally in forests over years of the leaf life cycle. Have you ever noticed that rich dark brown stuff on the forest floor? Now you know what it’s called. Some leaves contain weed-suppressing chemicals. Leaf mulch suppresses weeds, conserves moisture, attracts earthworms, protects plants from winter’s freezing and eroding winds, and improves soil structure.