Leaves are one of the most valuable compostable materials for the large amounts of fibrous organic matter they supply. Leaf compost serves primarily as an organic amendment and a soil conditioner. They improve structure of all soil types. They aerate heavy clay soils, prevent sandy soils from drying out too fast, soak up rain and check evaporation. Composting is becoming a main way to deal with leaves instead of burning and sending to a landfill.
The decomposition of leaves takes a quite long time. It could be usually about one or two and even more years. Besides, leaves have a tendency to mat down into a tight mass, create an impenetrable barrier to air and water. Shredding the leaves is usually required to solve these two problems.
This will reduce the bulk of the leaves by about two thirds, reduces the tendency of the leaves to mat, and speeds up the decomposition process as more surface area is bared to the decomposers at work. Besides, mix shredded leaves with a high nitrogen source such as grass clippings will do much help. Most leaves are in the “browns” or high carbon category of the compost pile. This means they contain much less nitrogen, while nitrogen is the one factor that starts compost heap heating up. High nitrogen materials, such as fresh grass clippings, old vines or other plant wastes, fruit waste and vegetable peels, etc., can speed up the decomposition process and increase the nitrogen content of the end product, making it more suitable for use as a soil amendment.
However, too much nitrogen can result in the formation of ammonia, creating an odor problem. The rapid decomposition also uses up oxygen, causing an anaerobic condition which greatly reduces the composting rate, and produce unpleasant odors. So the high nitrogen component must be carefully controlled. A healthy compost pile should have about two-thirds carbon (brown) materials and one-third nitrogen (green) materials. Take grass clippings as an example, an mix of 2 to 3:1 (leaves: grass clippings) is generally considered the optimum choice. A high-nitrogen fertilizer added to the pile may speed up decomposition.
Not all leaves are compostable. There are some leaves that should take caution.
1. Poisonous Leaves such as oleander, hemlock and castor bean. They can harm soil life, so add very sparingly.
2. Acid & resin leaves such as eucalyptus, bay and laurel, juniper and cypress and acacia. They are toxic to other plants and soil life. Add sparingly or not at all.
3. Cottonwood, poplar, and ash are pH imbalancers that raise the pH in soil, making alkaline soil more alkaline. They should be added sparingly. Rhubarb should be used sparingly because its oxalic acid content lowers soil pH.
4. Plant leaves with rust, fungus, mildew, or seriously infested with insect pests are best to take to the landfill. In theory, the heat from the composting process will kill disease spores, but in practice not all compost piles attain maximum heat potential.