September is a fine garden month, and gardeners can spend most of it simply reaping what they've sown. It's the season of the harvest moon, but it can also be a season for gambling, and gardeners who are willing to take risks in September stand a good chance of cleaning up later on.

In the Washington area, the season is changeable. Light frosts could hit in a month or so, but they could be followed by another month or more Indian summer.

That's where the gambling comes in. You can make the most of your garden's space, and bet your time and labor on a good season. The risks aren't that great, and neither are the jackpots, but the rewards are still worthwhile.

You can begin by moving any late crops you have that are growing crowded in rows. Give them plenty of space, and move them with plenty of earth. You might lose a few in the shuffle, but the survivors will fill out faster with lots of room.

Sowing more seed is where it gets risky, but even in a cold season you can't lose by planting fast-growing, cool-weather crops. Spinach, arugala, corn salad, mustard and a variety of other greens, planted now, will almost surely yield food before winter. Plant radishes and you can harvest them for Thanksgiving dinner.

With lettuce, kohrabi, turnips and other medium-season crops, the risk is greater but not outrageous, especially if you plant crops that can be eaten in the early stages of growth. A harvest of crisp baby turnips or tender leaf lettuce, late in the season, is infinitely better than no harvest at all.

There are some steps you can take to reduce your risks, but really, what are you risking? If your garden gets on early and killing frost, you'll lose what you spent on seed, and the time you put into preparing the ground and planting. But you should clear the ground as crops finish producing anyway, and you probably have seed left over from spring, too. Why not take a chance?

If your garden is in town or the near suburbs, you have an advantage over country gardeners when it comes to late crops - your risks are reduced. The pavement in cities holds the summer heat longer, there are no open plains for freak frosts to flash over, and the growing season is extended.

My brother's city garden is about 40 miles north of my country plot, and he often gets an extra month of growing time after frost has leveled all but the hardy crops in my garden.

And even though most country gardeners wouldn't trade for city plots, even for a longer season, there's something to be learned from the way that cities trap heat that can be applied to country gardens.

A rock mulch, for instance, will work the way city pavement does - it will grab some heat and hold it. A black plastic mulch - black absorbs heat - will operate on the same principle as a black-topped parking lot, scorching in summer, but starting to feel pleasantly warm when the weather gets cool.

Set your gamble crops in the sunniest part of your plot and try to trap heat for them. You can build portable cold frames around small beds by sinking planks into the ground and covering them with glass. Old lumber and storm windows make the cheapest, simplest cold frames.