The best time to plant and to transplant trees and bushes is when the leaves begin to turn. The heat no longer withers foliage, and the roots have a few weeks to spread out before frost hardens the ground.

I can think of no better way to chase away the gardener's fall blues -- all those negative thoughts about winter's dread hand -- than to plant a fruit tree. And the ideal fruit tree for most front and back yards is a dwarf (between eight and 10 feet tall) or a semi-dwarf (up to 14 feet). Dwarf fruit trees are easy to reach, easy to take care of, and they take up much less space than standard trees.

"Modern dwarf varieties make it possible to grow 40 apple trees in the space needed for just four standard trees," says M.C. Goldman, in the September issue of Organic Gardening magazine. "You can set dwarfs about 12 feet apart in both directions, or in 15-foot-wide rows spaced eight feet apart."

Like full-size fruit trees, dwarfs prefer full sun but will make do with a little less. If set out during the fall, they are capable of producing fruits the following summer, and the fruits are not a bite smaller and no less tasty than those that grow on standard trees. They tolerate underplantings of vegetables and flowers; they can be espaliered against a wall.

There are dwarf trees that have been bred, but most dwarfs available today were created when a standard tree was grafted onto the rootstock of a dwarf.

Mitch Baker of the American Plant Food Co. on River Road says that he has seen a steady increase in sales of fruit trees over his seven years as tree manager. Baker recommends Prima apple -- "a good tree to start with" -- and North Star Cherry -- "a real star, heavy bearing and easy to care for." Prima needs another apple tree for cross pollination, he adds, but plenty of other fruit trees are self-pollinating. "But whether you like peaches, pears or plums, you can have a good dwarf tree these days," Baker says.

The most important thing about planting fruit trees is to follow the recommended pruning and spraying schedules, Baker says. Though most people prefer having a harvest the first summer, in the first two years it is better to prune the tree severely and thus forego a big crop, in order to let the tree establish "a good framework" -- a sturdy alignment of branches -- and a healthy root system.

Behnke's, one of the largest nurseries in the Washington area, sold about 2,000 dwarf fruit trees last year, says manager Helmut Jaehnigen. Most people plant fruit trees in the spring, he says, but the fall is the better time. He points out that the tree, six or seven feet tall, selling at $24.95 in the fall, is one year older than the tree selling at $17.95 in the spring.

A good place to size up the possibilities of a home orchard is on River Farm, originally owned by George Washington and now the headquarters of the American Horticultural Society. River Farm has a demonstration orchard of more than 60 dwarf and semi-dwarf trees, all labeled. The curator, botanist Steven Davis, is an enthusiast of the back-yard orchard; he praises the disease-resistant and easy-to-care-for features of the new varieties. For the Washington area, he recommends Sir Prize apple and Shiro plum. For a typical 10-by-20-foot area, he suggests six dwarf fruit trees.

Just off George Washington Memorial Parkway in Alexandria, River Farm's 1,800 landscaped acres are open to visitors from Monday to Friday, between 8.30 and 5. Sunday, Oct. 17, is open house, with bulbs, gardening books and refreshments for sale. Dr. Henry Marc Cathey, director of the U.S. National Arboretum, will lead a walk through the farm, and other experts will be at hand to answer gardening questions.

Mulch heavily if you set out your onions in the fall for that early, early spring harvest. Experts predict an unusually cold winter -- some say the coldest winter in memory is in the offing--and if that is so, eight inches of straw, spoiled hay or shredded leaves is not an exaggeration but a minimum to keep the bulbs happy.

Q: My front lawn of Zoysia has been badly damaged this spring and summer by moles. I have tried Chlodone dust and moth balls, but none of these has proved effective in stopping their burrowing under. Do you have an answer?

A: A three-pronged counterattack is recommended by Robert Schery, retiring director of the Lawn Institute, an Ohio-based nonprofit research group:

One, to eliminate grubs and insects, the moles' food supply, use a heavier than usual dose of insecticide. (Insecticides now outlawed by the Environmental Protection Agency are the best, Schery adds.) Two, to beguile the enemy, poisonous baits ought to be dropped into their tunnels. (A chemically treated peanut has proved to be particularly effective.) Three, to capture, maim or kill, traps are best.

Dr. Schery points out that there is no single guaranteed, foolproof way to win the war against moles. But a combination of these three approaches is going to work.

Phone calls to a number of lawn experts yielded what may well be an emerging consensus on an organic defense system: A flower known as Crown Imperial exudes an odor offensive to moles. Burpee's catalogue describes the plant as having "regal clusters of large, bright, gracefully drooping flowers with a green crown of leaves." One horticulturist who has tried it says that "when moles bump into the Crown Imperial, they go in the opposite direction."

The hardy, bulbous perennial has the resonant botanical name of Fritillaria imperialis. It comes in red, orange and yellow; Burpee's price is $4.95 per bulb. Even if some moles turn out to be less sensitive to its scent, Fritillaria imperialis is a showstopper as a border guard.