The best time to plant a tree was 20 years ago; the second-best time is now, according to one Chinese proverb. One acre of forest absorbs 6 tons of carbon dioxide and releases 4 tons of oxygen-enough to meet the annual needs of 18 people, says the U.S. Department of Agriculture. And, with its cool nights and pouring skies, fall is the time to plant because the warm soil coaxes new growth from roots.

Organic Gardening has a trick or two up its sleeve to aid and abet newbie tree gardeners. It also busts some commonly held myths, such as the need to lop off your topgrowth to compensate for your nursery-grown plant's smaller root system. The real deal: Just-planted trees need every leaf they sprout, or they won't rustle up enough food for healthy growth. ::Organic Gardening

Difficulty level: Easy