LEFT TO her own devices, Mother Nature goes to pot in August, and the gardener, if he does not look ahead, will find himself with a ripe hay-field on his hands at the end of summer.

Of course, water lillies are at their best, but I think I have already said that nothing in a garden is so rewarding as a pool for lillies and fishes. Once it is thought out and durably constructed - which does not necessarily mean concrete - it is a joy through the years.

There is just one thing to mention here, and that is that greediness defeats itself. if more than half the swater surface is covered with lilly pads, the pool will look as if you are raising a salad crop for the market, and yet the poor gardener is on fire to grow a hundred different sorts of water lillies. If his aim is to see how many blooms he can cut from water lillies, then he may as well jam the plants in.

My own pool has a water surface of 100 square feet, and I find that two water lillies, "Marliacaes Chromatella" and "James Brydon", a yellow and a red, respectively, are plenty. i have "Yellow Pigmy" and "Pink Butterfly" as well, but that is pushing it.

I could have twice as many, but I would not like the effect, and I would suggest, for a 10 by 2-foot pool, two vigorous hardly kinds lillies, omitting the hardy kinds, except I would grow "Yellow Pigmy" and another small one so there would be pads floating in the spring, because the tropical lillies are not set into the pool until June.

Gardeners enjoy making their own mistakes, learning as they go, but if anybody wishes to save himself the bother, let him do it this way: a pool as large, not as small, as can be managed; two feet deep, one water lilly for 25 or 35 square feet; one fish for every two cubic feet of water.

Also, plenty of submerged water plants, no filtration system, a once-a-year change of water the end of March or in April, no chemicals to clear up algae, one good-seized plastic tub for each water lily holding half a bushel or a bushel of soil on the heavily side or good heavy loam with no sand, no leaf mould, no manure and no fertilizer to begin with.

Still, I rather enjoy thinking of the gardeners who are jamming in a water lilly for every 10 square inches and a fish for every 20 square inches of surface, and who are fidding about with filter systems that do not work in water two deep and that have visible apparatus - gardeners in a great sweat to do everything right, but deliriously unsure as yet what rightness consists of.

Someone asked me what I had to say of a water lilly form's recommendation that 10 water lillies, and I said I had nothing to say about it except that I know better than they do how to make it look the way it should. I suppose if you asked The Washington Post how many subscriptions you should get, they would say, "Well, 15 is about right."

Let me go one useful step farther, and not leave the budding aquatic gardener crushed that he can have extremely few water lillies in his pool.

He could keep his pool beautiful by exercising the restraint I have just urged, then he could get half-barrels (the whisky has to be got completely rid of, which means scrubbing and weathering) and grow one water lilly in each barrel. Thus he could work in a great many, in barrels suck back near a sunny garage, etc., and have the esthetic pleasure of an uncrowed pool the plantsman's joy of many differnet varieties in the barrels.

August is also the month for cannas. Great gardeners, I notice with satisfaction, are usually fond of cannas.Where I grew up, you saw cannas in the slums and around hovels in the fields, so snobs came to think cannas were mean plants.

Nothing else makes quite such wonderful sheaves of folliage, and it is too much of a blessing to believe (yet it is true) that flower colors in cannas tend to be pure and sparkling. I have "Wyoming" or "King Humbert" with bronze-purple leaves and clear sparkling vermilion blooms.

Sometimes they look well grown several together (of one variety) in a clump, and less well sprinkled here and there like exclamation marks, or lightning bolts. Needless to say, billows of gray foliage (artemisas, tamarisks, anaphalis and the like) set off the purple-leaf cannas habdsomely, while marigolds and zinnias nullify the drama, by compeing too strongly.

Japanese anemones begin in August. Nurserymen have taken it into their heads lately that they do not have to grow Japanese anemones, especially white ones (the handsomest) so one has to shop around. They are among the most permanent of perennials, and should be given places of great honor, since their cut-leaf foliage is good from the time they come up (rather late in spring) until frost, and the clusters of bloom, like waxy half dollars either white or pink are borne on good stiff stems two or three feet high.

They are especially handsome with box or yew (or mahonias or evergreen privet or holly) as a background. Small town gardens should always have at least on clump.

The bughanes (which are supposed to chase bugs off but, of course, do not) are beautiful for late August and September.

I foolishly planted just one, in fairly heavy shade. I should have planted 10 in a little patch, so they would really look like something, at a time little else of note is in bloom.

The wild Japanese clematis, which people keep pointing out it is one of the most distinguished and valuable of all vines (and far more elegant and showy, too, thah most of the other clematis people have fits over), begins blooming in mid-August and goes well into September.It is a cloud of lacy white flowers heady with an almond scent that people dislike.

A great favorite of everybody who grows it is the Russian sage or preovskia, with almost white aromatic leaves and stews and every narrow spikes of mid-blue flowers, very like a sage. It is semi-woody but very light in effect. Many of us like dumpy things that grow like blobs - irises, hemerocallis, roses - and I am embrassed to say I am mad for all of them, though I know how tiresome and dull their foliage is if there's much of it. In this age of flat outright lies, you can read that daylilies and irises have fine foliage, and then wonder why they look so dull in your own garden.

I will tell you why. They have hideous foliage, in the sense that it turns brown at the tip or goes yellow and rots. But even if it doesn't, it is dull because we tend to grow a lot of irises and daylilies, so that even if one or two clumps would not be dull, yet many clumps are extremely dull.

That is why gardeners fall irreversibly in love with things like the Russians sage. A patch of irises, if set off by an iron fence and a fat clump of perocskia growing through it, will be less of a curse all summer than the same patch baking nicely in the sun.

And yet such plants as this perocskia, though telling in effect, do not take all that much space and are so light they do not shade other things out. Yet it is sturdy and is not itself choked out. that is why such plants are treasured, but you must discover for yourself what they can do before you understand why young gardeners - I almost said old ones - like myself admire them so.

A rose I am not all that wild about, but which I would not fail to plant, is the white (touched blush in summer heat) "Mme Alfred Carrierre," climber, usually classed as a Noisette.

It blooms constantly, but is more vigorous than gardens with an eight-foot length of fence might want. It is the best white climber for Washington, if you value health, hardiness, scent, moderate sixe, doubleness of bloom and constancy of production.

I used to grow "Lamarque" which is a bit too tender, and it is such a famous rose I tried very hard to be passionate about it, but the truth is I never like it much. "Climbing White Manan Cochet" likes to grow 35 feet a year, or did with me, its flowers are superb but it does not bloom much in summer (though the bush variety does) and it, too, is more tender than you think it is going to be.

People are going to some famous garden or other and coming back awestruck at this or that. If you tell them the rose they admired on the cottage at Sissinghurst was "Mme. Alfred Carrierre" they said oh, and plant something else and wonder why it doesn't look like Sissinghurst. You flat would not believe how gardeners operate.

I suppose many people grow aconites or monkshoods, which are gloriously blue as summer turns to fall. Somehow I have never grown

Phlox is hanging on well, and of course there are dahlias.

An outrageous infestation of blindweeds has been neglected here, and I do not in any waydeserve the considerable number of dahlias that glisten like rose and sulfur moons in their astral embrace.Irises must be hand-weeded, there are no two ways about that, and dahlias are so good-natured that they often suffer from neglect.

When an urn became vacant through the death of its occupant, I stuck in a handful or two of Sedum spurium, which I suppose means bastard sedum, a harsh name for so handsome a love-child. In a week or two it adjusted and flang itself over the cherub (the urn has a cherub head sprouting wings) in a smoldering cloud of madder getting on toward purple.

You would have thought I had thought about it.

Gardening is bitter - someone observed it consists of 11 months anxiety and one month's disappointment - and yet time and again things turn out so much than we ever planned for them to.

A garden planned for the late August and for January will give pleasure, because spring and early summer will take care of itself. Even a little thought, both for August and for January, will go far in keeping the gardener from muttering and snapping.