PEOPLE CAN talk all they want to about "painless gardening," but they aren't talking to those of us who long ago took our black thumb and hitchhiked away from the farm. Summers spent with granddaddy on a Georgia farm so bad he had to make his living from preaching gave one little faith anything put in the ground would ever come up no matter how much fertilizer, mulch and water was put on it. For us the only painless gardening is no gardening.

The concept of the "backyard" as the garden is new-fangled anyway. Front yards in Valdosta were, of course, elaborately tended, with grass, mixed annuals, a row of camellia bushes and at least one each of pecan and mimosa. The backyard was for the scuppernong grape arbor, the fig tree, the dog kennels and the garage. Nobody in his right mind would sit outside because: (1) It was too hot; (2) The mosquitos would give you malaria; (3) The gnats would drive you crazier than you were to begin with.

Washington, after a string of 90-plus days, is clearly recognized as a tropical post. (The English knew it long ago and used to furnish their military attaches here with short pants and pith helmets.) Perhaps it is time to listen to an authentic born-and-bred Georgian from Valdosta on the subject of how to keep your cool in the backyard.

My husband and I have done a considerable amount of research on the subject, especially since he not only has a Southern upbringing but also hay fever. He thought of laying astro turf in the yard here and installing wrought iron trees, painted green in the spring and rusting through until fall. When that wouldn't make the frog jump, we settled on another alternative. After two years the idea we decided upon works just fine though admittedly, what with the contempt of modern youth for the lawnmower and the penalties for child abuse, we are going to swap the rest of the grass for Baltimore flagstone just as soon as we get the money.

What we did was call up Bill Moeller and ask him build us as big as swimming pool as we had money for. Our money ran out at 12 by 36.

The pool depth goes from 3 1/2 to 5 1/2 feet. This shallow depth works well for us, because I am afraid of diving. Because the pool is shallow, it heats up quicker in the spring, uses less water, takes less filtering, ect. I would have liked it 4 1/2 to 5 1/2, but Moeller insisted a subsequent owner would like a shallower depth for children. As for subsequent owners, if I can't take the pool with me, I'm not going.

We wish we had made it wider. As it is, if three people are swimming laps, you need a Maritime Commission. We didn't make it wide, not only because of the money, but because the chief ornament to the garden before the pool came was our 60-foot-high magnolia tree. It hasn't been pruned within our memory and at least one branch artfully drapes itself along the pool edge. The magnolia is so obliging it even blooms along that branch when we have parties. The magnolia's kissing kinship with the pool is an idea that worked out better then we could have hoped.

We have a lilac tree on the other side, and a mulberry that keeps coming back even though we chop it down and curse it. I said the pool makes for painless gardening. But to tell the truth, a pool that nuzzles trees needs perpetual dredging. During the swimming season it isn't quite so bad, because you can make a game of swimming around chasing leaves.

At the far end of the pool, we had a line run for a fountain. We could have had a nymph pouring water from an amphora, or a dolphin with water gushing from his mouth. We settled for a husband-made sculpture of objects we had found that looks like a monstrous bug on wheels. We call it "Hell on Wheels." I love it, but each to his own opinion. We wouldn't think about a pool without a fountain. There are many Washington artists, such as Slaithong Schmutzhart, for instance, who make something of a specialty of fountain sculptures. Such one-of-a-kind artworks don't cost much more than those unappealing plaster cherubs.

The pool steps are of concrete and are tucked into one corner to save space. There was an aluminum ladder and handrail to satisfy the city pool inspector.

We put the pool as close to the house as possible, just off an existing flagstone patio and a screened (since glassed) porch. If we crane our necks a bit, we can see it from most rooms of the house. We wish it were possible to see if from every room, without craning, because it is by far the mos ornamental part of the yard.

If you site your pool close to the house, either provide a path of ceramic tile to the bathroom, or an outdoor cabana, or be prepared to mop. So far, we use the latter method.

We chose to make our pool black - the coloring is integrated into the last coat of concrete. Not all pool builders are prepared to do this, because, they say, the color comes out a bit unevenly. Shop for a builder who will. The color is the best decision we made. The black pool becomes an ornamental pool, a reflecting pond, mirroring sky, trees, flowers and whatever you put close to it. In contrast, white, natural, blue and green pools have something of the health club of gym look to them. The black pool fits into the local landscape insted of sticking out like an exercise bicycle. Leaves floating in it make it look even more like a natural pond, though I'm not recommending you leave them in.

Instead of the concrete apron, beloved of the jock landscapers, we used Baltimore stone, a heavy, rough, thick stone with a brown-mauve color. The stone extends slightly over the inside pool edge to give a hand grip. We used a dark mortar (black powder, the same used in the finish concrete coat). We didn't get it dark enough. Unfortunately my husband and his helpers laid the stone just the day before the people came to put on the finish coat. Their wheelbarrows running over the stone loosened the mortar and some had to be set all over again. The freeze of last winter loosened one as well. But we are veryhappy with the stone because it adds to the naturalness of the pool. The stone, by the way, costs only about $1 a square foot, much cheaper than many alternatives. Brick or quarry tile would look good, too, though perhaps cost more, take much longer to lay and be less natural and more sophisticated.

Because we barely could pay for it, counting pennies and foregoing all vacations for five years, we had no fancy extras like built-in push-button pool covers, underwater lights, automatic pool cleaners, etc. We put on a pool cover manually every fall when the leaves are at their worse. I like to take the cover off immediately thereafter, but my husband, who is the chief leaf extracter, would rather wait. I hate the look of a covered pool. Even in the winter, an uncovered pool is a great ornament to the view, especially when it freezes.

We have outdoor electric lights of a primitive nature, but for most purposes we like to use the candle-filled heavy glasses, made in Latin America and sold in the Spanish food section of the Chevy Chase Safeway and other stores catering to the Spanish-American trade.

We did not have a pool heater installed. With the size of our house heating bill, I'm glad we didn't. One of these days, when our ship comes in and docks in the pool, we'll have a solar pool heater, I hope one that will serve to heat the domestic hot water during times when we don't want to swim. I am waiting to see how President Carter's works out.

As for gardening - oh yes, we were going to talk about gardening. Well, we water the magnolia tree every time we think about it and cut down the mulberry tree every spring. On Earthman's advice, we did push a few daylily roots or sprouts or whatever they're called in around two sides of the pool. At this time of the year they look mighty pretty, though in early spring I thought I had my granddaddy's luck, because nothing seemed to be poking its head above ground except for the pokeberry, which seems to thrive near the fence.

If we had it to do over again, we wouldn't put up that dinky stockade fence that cost so much money (though it was the cheapest thing we could find other than chainlink fence, which to us is only fit for dog runs).

Given our druthers, we would have a brick or a stone wall on all sides, preferably 12 feet high. Nothing but a masonry wall will ever look quite right with this pool.

And we would enlarge the pool to cover the entire yard, leaving only an island for the magnolia tree; though, I suspect, that mulberry would poke its head up through the drain.