If you let August slip by without planting fall crops such as sugar snaps, lettuce and cauliflower, and you do not have a flat of spinach or broccoli seedlings ready to be transplanted outside, you may still throw some radish seeds on the ground and qualify as a fall gardener.

If you are adventurous -- and lucky enough to have a garden in a nook protected from wind -- you may still try planting leaf lettuce, and even spinach, Swiss chard and snap beans. Plenty of gardeners like to defy conventional wisdom and get away with it when assisted by a balmy Indian summer.

Last weekend, Byron Williams, a Department of Housing and Urban Development employee, planted radishes, kohlrabi and several different kinds of lettuce at the 40-by-60 demonstration garden between Independence Avenue and Sixth Street SW, across from the Air and Space Museum. He works there on weekends and during his lunch hour. "I was encouraged by the sunny Labor Day weekend," Williams said. "I thought it was worth a try. There is enough heat left this season to give these plants a start."

But this week is pretty much the last reasonable chance for getting a fall garden going. The days are getting shorter and the nights are cool, and most vegetables require a long, warm growing season undisturbed by cold spells. The first fall freeze will be between Oct. 17 (in College Park) and Nov. 2 (at the National Arboretum, Northeast Washington), according to weather data accepted by the Men's Garden Club of Montgomery County and published in its handsome, practical booklet, Successful Gardening in the Greater Washington Area.

That first freeze, however, is seldom a killing freeze, and a lot of cold-weather vegetables can survive it. The rule of thumb is that in the Washington metropolitan area, ordinary outdoor gardening -- as opposed to cold frames and other season-extending devices -- is possible until mid-November, provided the plants are firmly established before the cold weather begins.

Radish is the one fall crop that is the safest bet at this late hour in September. The U.S. Department of Agriculture recommends the radish as the fastest-maturing garden crop; children like it because of its crunchiness. Sliced thin or carved in the manner of a rosette, it is an esthetically pleasing addition to a tossed salad or to the hors d'oeuvre tray.

Radishes wilt in the heat but thrive in cool weather. Their demands are few: The soil should be moist and not too compact -- radish is a root vegetable and its bulbous roots like a soft environment for their expansion. A handful of fertilizer or a thin layer of compost scattered on top of the row ensures a tastier and speedier crop.

Radishes germinate promptly and reliably -- so sow the seeds several inches apart. The small varieties, such as Scarlet Globe and Cherry Belle, have a mild taste and you can start digging them up 20 days after their sowing date.

If radishes are not dug up in their prime, they have a tendency to turn woody or mealy, and their taste can become unpleasantly sharp.

The larger varieties (such as Long Black Spanish and China Rose) are pungent and known as winter radishes. They take longer to mature -- more than 70 days -- and it is risky to sow them outside now. But they are ideal candidates to grow in a cold frame and can be stored like other root vegetables.

A smart tip for strawberry growers comes from Dr. Darrel Apps, a horticulturist at Longwood Gardens in Kennett Square, Pa.

"June-bearing strawberries tend to get much too thick at this time of the year," says Apps. "Take them out, separate them and replant them. Cut off their runners and replant them too. Water them often and keep the soil moist."

Apps promises that the strawberry bed thus treated in September will bear heavily next June.

Q: My vegetables -- cucumber, tomato and pepper -- flower nicely, even profusely, but after the flowers drop off, very few fruits develop. Is there something I could do?

A: Fruits do not develop if the temperature is too high or too low or if there is too little or too much moisture. But in a well-tended garden, insufficient pollination may be the problem. You could pollinate the plants individually -- with a small, soft artist's brush or even a pensil -- but the process is laborious and uncertain. Bees do a much more thorough job, and there are a few plants certain to attract them. The perennial monarda has a lovely scarlet flower but a tendency to take over a larger territory each year. Bees love all varieties of the black-eyed Susan (marketed as Gloriosa Daisy) as well as its close relative, the purple coneflower. A border of a few clumps of any of these flowers will dress up your vegetable patch and make bees regular visitors to your garden.