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Have you noticed the fall color this year? Maples, oaks, sweetgum, and birch developed particular depth of color and are still glowing against gray skies. Or perhaps color in fall always surprises gardeners with its intensity and variety. One garden writer and observer, Allan Lacy, said "in fall there are colors we have no names for." I think of this when attempting to describe the beauty of a grape leave, turned to amber and gold, with red veins outlined in late afternoon sunshine.
To add fall color to the garden, pick plants at nurseries and garden centers when they are in colored leaf. Trees and shrubs will vary within the same type; some are genetically more brilliant than others. A favorite in my garden is Acer palmatum ‘Ozakazuki,' deeply crimson in fall. This tree alone sets a mood of celebration.
Against the joy of fall color is the descent, and some would say, the deluge, of fallen leaves. This past week a number of Sunday cartoons depicted the plight of leaf rakers, and the reluctance to rake. One showed a gardener surrounding his tree with open bushel baskets with the caption "you really hate to rake, don't you?" Many of us remember the smoke of leaf fires along road edges in fall, even within residential areas of cities. Now that they can't be burned, what can be done with fallen leaves? It would be helpful, as part of the celebration of autumn trees, to consider the many garden uses for the leaves.
Remember the springy feeling of walking on a forest floor? The fallen leaves, twigs, needles, and other natural materials in a forest decay into a nourishing mix called "duff." Duff is a natural mulch created from the slow decomposition of these materials, providing nutrients for trees and other forest plants. If we, while gardening, begin to see the usefulness of fallen leaves, the chore of raking may diminish.
Leaves make good mulch for shrub beds and perennial borders. Specifically, the best leaves for this purpose are medium to small: smaller maples, birch, aspen. After weeding the beds for winter and planting bulbs, simply dump or rake leaves to a depth of 2-3 inches. These don't have to be pre-composted, but placed on just as they fell. These smaller leaves will gradually break down and add nutrients to the soil. Worm populations like to multiply under leaf mulch, and this strategy will benefit both sandy/gravelly soils and stiff clay soils.
Some garden debris doesn't make good mulch. Don't use any weeds or leaves from fruit trees with disease problems such as apple scab, or from dogwood afflicted with anthracnose. Discard these in ‘clean green' collection or trash collection. Broadleaf evergreens such as laurel, rhododendron, and conifer needles decay very slowly and aren't as satisfactory as mulch. A pile of mixed broadleaf evergreen leaves would eventually turn into compost, but the process can take several years.
Huge leaves with prominent vein systems and lots of fiber, like bigleaf maples, are also less than satisfactory in mulch. They become slippery over winter and mat down without breaking down sufficiently. If it's possible to shred or chop these leaves, as with a shredder or even a lawn mower, they will be useful as mulch.
Chopped and shredded leaves also make quicker compost. Admittedly, shredding leaves requires patience and proper equipment. Hoppers are often too small for armfuls of leaves, and wet leaves choke the shredder. At least, they choke mine. I still use a vintage 1973 shredder which is basically a lawn mower at the bottom of a hopper. The ideal is getting at shredding when leaves are still dry and crisp. If you've discovered that your equipment and time coincide to allow you to shred leaves, there's no finer garden amendment.
Making compost with fallen leaves is easy, even without shredding them, though like all compost, leaves decay faster when shredded or chopped. A mixture of leaves and cut grass breaks down into useful compost in about six months with very little turning. If your garden has space, just piling the leaves alone in large heaps (at least 4 feet by 4 feet), and allowing them to break down naturally, will provide excellent leaf mold at the bottom of the pile in about a year. Leaf mold, the crumbly brown result of leaf decay, is a prized addition to garden soils and potting mixes.
Washington State University WSU Extension offices have good publications on composting techniques. For information in Pierce County, call 253-798-7170 from 9AM to 3PM weekdays. In King County, call 206-296-3900 from 9AM to 4PM weekdays. And in Snohomish County, call 425-357-6010 from 10AM to 2PM Monday through Friday (these are the winter Master Gardener hours.)
Leaves provide the carbon part of the necessary carbon/nitrogen breakdown that keeps compost heaps churning and active. If space permits, save bags of leaves to use in summer compost, because the autumn leaves provide perfect balance to masses of summer lawn clippings. Storing multiple bags of leaves beside the compost bin makes sense and keeps the grass accumulation from getting out of balance and causing the messy, smelly pile that results from too much nitrogen (green material like grass) and too little carbon (brown material like autumn leaves, sawdust, or straw.)
Bags of stored leaves, in plastic bags, make good insulation for container plants in case of heavy freezes. Group the containers and surround them with bags of leaves; this provides a rapid way to shelter containers in sudden weather changes.
If weather permits, don't neglect scuffling through fallen leaves or even diving into a big stack raked up on the lawn. Imagine what we'd miss if leaves never cascaded off trees in the fall!
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