Autumn Leaves - Myth and Reality

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Published on: Oct. 2, 1995

Last revision: Oct. 20, 2010

You can use composted leaves to improve your garden, trees and lawn.

What a waste!

Every autumn, trees rain down nutrient-rich leaves that can improve our gardens, fortify our trees and shrubs and make our lawns luxuriant. And what do people do with this bounty of nature? They rake the leaves up and burn them or, worse, bag them and dump them illegally.

Leaves make great fertilizer and wonderful mulch. They build topsoil or humus. It's a simple formula: year after year, the trees shed the materials you need to make your yard or garden more beautiful. All you have to do is use them.

Sometimes leaves require special handling, such as composting or chopping, but all leaves can be recycled. The rest of this article both tests your knowledge about leaves and provides you with the latest information about reusing leaves. See how many questions you can answer correctly.

Leaves make a good mulch to mound around trees and shrubs.

True. Spread them about a foot thick in a flat doughnut shape as far out as you like, to under the tips of the tree branches.

You can't use oak leaves on your garden because they're too acid.

False. As oak leaves rot they lose their slight acidity, and the oak leaf mold ends up alkaline. University of Missouri Extension advisors say to test your soil and add lime if necessary to raise the pH.

Foundation plantings need to have leaves raked out from under them in the spring.

False. This practice must be a holdover from pioneer days, when everything combustible, including leaves and grass, was kept away from wooden cabins because of fire danger. Moist leaf mulch under foundation plantings keeps shrub roots cool, keeps weeds down, and keeps the soil moisture from drying out so quickly.

Bark mulch is better than leaf mulch.

False. Bark mulch is a handsome ground cover and can be used anywhere away from buildings. But it contains shreds of wood and has been known to attract termites.

Keep bark mulch at least 20 feet away from any buildings. Make costly bark mulch go farther by piling leaves on as mulch first, then sprinkle bark mulch on top. Both kinds of mulch turn black as they age, give a nice appearance and add valuable organic matter to the soil.

You have to wait three years until leaves rot into leaf mold before you can use them in flower or vegetable gardens.

False. November's leaves can be dumped onto perennial beds, under trees or into a compost heap. Annual flower or vegetable gardens should be cleared of frost-killed vegetation (compost it), sown to a cover crop like annual rye or hairy vetch and left to grow all winter. The cover crop should be dug or tilled in the spring, and two weeks later seeds may be sown.

By the time long-season crops like corn or tomatoes are about 10 inches tall, the rough compost from the previous November's leaves may be spread 4 inches thick between the rows. It will pack down to about 2 inches thick, and can be dug or tilled in during the fall, before the new cover crop is sown, or in the spring. Freeze/thaw cycles, earthworms and other soil decomposers will help break down the leaves even further. Garden soil will turn black and rich in organic matter and fertility.

Leaves kept in bags until spring can be spread and tilled in then, just before seed is sown.

False. Seedlings won't grow well if the dirt is overloaded with unrotted leaves. Empty the bags, let leaves rot for 9 months. Weed seeds will be denied the light they need to sprout if you hoe or cultivate first, then mulch row middles with rotted leaves after plants are growing well.

Maple leaves rot faster than oak leaves.

True. Thin green nitrogen-rich maple leaves, which fall to the ground in early autumn, will rot quickly. Thicker oak leaves fall later and rot more slowly.

Scientists have found that fallen maple and oak leaves release natural phenols during the first 6 to 8 months of the rotting period. These phenols inhibit growth of seedling roots, but rot and disappear from soil and mulch within 9 months of weathering. Better to keep dead leaves and leaf compost out of an area where seeds will be sprouting until after plants are up and growing well.

Pine needles are a good, long lasting mulch for acid loving shrubs like azaleas and rhododendrons.

True. A resinous covering on the needles slows rotting. Pine needles can also be sprinkled in a thin layer over oak or other leaves to keep leaf mulches from blowing. Pine needles are best left under pine trees, where they protect roots from drying. Another way to keep a leaf mulch from blowing is to sprinkle it with water right after the mulch is laid down.

Lawn grass will die if you don't rake all the fall leaves off.

False. A rotary mower, run in a spiral clockwise pattern over a leaf sprinkled lawn (edge first), will shred most leaves into bits, which, like grass clippings, will be washed down onto the soil between the grass blades during the next rain. Earthworms will turn leaf bits and grass clippings into black humus topsoil around the grass roots.

Leaves only need to be raked off the lawn if the leaf layer is so thick that it blocks out the sun. If so, rake them into 2-foot thick doughnut-shaped piles around trees and shrubs where the grass is too shaded to grow well anyway.

Trees respond well to the leaf mulch like that found on the forest floor. Hose the pile once with a gentle spray to keep leaves from blowing away. Or sprinkle straw or pine needles on top to hold leaves down in a wind.

Leaves mixed half and half with grass clippings make good compost.

True. To get fast results, do not pack down but pile in a heap between 4 feet high and 8 feet high. A bin is not essential but may help keep leaves from blowing. Keep pile moist and turn daily. A smooth, rounded tine pitchfork speeds the work.

After 3 weeks of the natural rise in temperature in the center of the pile, you may spread the compost on your garden. By then it should have cooled down. Or leave it for 4 months, turning it once. It won't smell bad as long as air can get to the center of the pile.

It is wasteful to put leaves and grass clippings out for the trash truck to take to the landfill.

True. At present rates of use, Missouri's landfills will soon be full. About 20 percent of the material once sent to landfills from St. Louis County was leaves, grass clippings and other yard waste. A Missouri law now forbids landfilling of yard waste. Landfills now compost truckloads of yard waste and sell the compost.

Labor and hauling costs to large scale compost sites are considerable. Save money, don't bag leaves and grass. They're so valuable for adding humus to the soil that the home owner should use them on his own grounds. I've done it for 30 years.

Last winter I had 10 tons of compost dumped at the end of my driveway. I spread it on my garden and flowerbeds and raked it onto my lawn an inch thick. My lawn now is thick, lush and green.

The National Academy of Sciences places a high priority on soil and water quality.

True. Most of the soil in this country has lost 65 percent of its organic matter. Much clay soil in Missouri, having an organic matter content of 1.5 percent, can absorb only one-half inch of rain in a 24-hour period. Increase the organic matter content to 5 percent and it will absorb a 6-inch rain in a 24-hour period.

Every 1 percent increase in organic matter increases the water holding capacity by 100 percent. Keep the rain that falls on your fields and lawns from running off into flooding rivers. To help your soil hold that rain where it falls, give it rotted leaves, rotted sawdust and grass clippings.

The Environmental Protection Agency is talking about restoring the carbon content of soils, because a soil rich in fungi and plants will take up a great deal of carbon dioxide. Each 1 percent increase in the carbon content of soil helps to delay the greenhouse effect by 10 to 15 years.

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