Leaves: The 'Other' Fall Harvest

Fall -- that season of the year, as Webster's dictionary says, "in which many of the trees lose their leaves." The falling of leaves is so much a part of autumn, that the event has become the other name for the season.

Those of us blessed with deciduous shade trees in our parks, boulevards and yards face a lot of work when those leaves come down. Leaves that fall in a forest can slowly break down where they land. Leaves that fall on grass, however, need to be removed. A lawn can absorb its own clippings, which slip between the blades of grass, but even a light covering of leaves will cause grass to die back and be more prone to disease.

So the leaves must be gathered. Then, once leaves are collected, the dilemma of what to do with all this material presents itself. Landfilling or burning leaves seems like the easiest option to many but these are not the only or the best choices. Autumn leaves can be used in many ways in yards and gardens.

Mulch  Mulch is a layer of material that covers the surface of the soil. Many sensitive perennials winter much more reliably if they are heavily mulched with leaves in late fall.

Leaves saved from the previous autumn can also be used as a mulch around annual flowers and vegetables crops. Summer mulches are best applied once the soil is warmed and the plants are well established. Four to six inches works well.

Maple, ash, elm and birch leaves can be used as mulch just as they are collected. Heavier leaves, like those from cottonwood trees, work better if they are lightly shredded. Although you can buy shredders, a lawn mower can also do the job. Just rake your leaves into long, low piles and then run the mower over them, using your grass catcher (if your mower has one) to collect them. Another method of shredding the tough leaves is to put them into a garbage can and use a string grass trimmer to chop them up.

Compost  Autumn leaves are a great asset for the home composter. You can add them to the outdoor compost system year round. Dead leaves are high in carbon and are used to balance the higher nitrogen contributions from materials such as food scraps and green plants. You can make a good compost mixture by combining three parts leaves to two parts food waste or green plant material. A two or three person household that composts food wastes will easily use three or four garbage bags of leaves a year this way; if they compost grass clippings or green plants from their garden, they can use even more leaves (see saskwastereduction.ca for more composting info.).

Leaf Mould  You can encourage leaves to decompose without mixing them with other materials. Moist piles of leaves will decay slowly and produce a fluffy soil amendment similar to peat moss that many gardeners value. A faster variant of leaf mould can be achieved by supplying some nitrogen. You can use granular fertilizer or a purchased inoculant-nutrient mixture designed to enhance leaf decay.

Sheet Composting  Another time-honoured way to handle autumn leaves is to till them into garden soil. This is best done as early in the autumn as possible. Spread the leaves in a layer up to 4 inches (10 cm) deep and then till or dig them into the soil. The same sort of microbes that break down leaves in compost piles will decay them in the soil. To accomplish their work, the microbes need nitrogen, which they take from the available pool in the soil. This can create a temporary nitrogen shortage. Short-term fertility problems caused by adding the leaves can be avoided by adding some nitrogen fertilizer. You will need to add nitrogen particularly if the leaves are still very recognizable in the soil in the spring.

(Source: WasteWatch, October 2003)

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