IT OFTEN happens in small gardens that the lily pool is shaded by tree branches, either because the pool was built in the only available place, which was in shade, or because trees later grew (as trees have an unfortunate way of doing) to provide gross shade.

Old gardeners know there is no point planting any water lily in a shady pool -- one that gets less than three or four hours of sunlight falling on the water surface.

But then old gardeners learn this through painful experience. By reading, young gardeners can commonly save themselves a good bit of money, anger and time.

Well, suppose the pool is really shady, what then?

There are a few plants that may be tried. First, if there is some sun, though not much, there are a very few water lilies that may endure and flower a little though not as freely as in full sun.

Among the hardy water lilies that stand as much shade as any are the lovely 'Chromatella,' soft yellow; 'Comanche,' apricot-bronze; 'Gloriosa' and 'James Brydon,' both red -- and the last name often comes rose-pink in the shade.

Tropical water lilies that stand more than usual degrees of shading are 'August Koch,' blue-violet; 'Director George T. Moore,' often called navy blue, but with a bit of violet in it; 'Dauben,' smallish light-blue hybird (produced at the Oxford Botanic Garden in 1905) that exceeded my hopes in a shady spot. Often called a miniature, 'Dauben' can produce flowers 6 inches in diameter when well grown. Others suggested for shade are 'Panama Pacific,' purple; 'Patricia,' small red; 'Blue Bird' blue; 'Independence,' both blue and pink forms of this variety are in commerce; 'Isabella Pring,' white -- and I dislike both this one and 'Mrs. George H. Pring,' another white; to me they are less attractive than the colored sorts; and 'St. Louis,' yellow.

Both the water lettuce (Pistia stratiotes) and the water hyacinth (Eichhornia crassipes) stand more shade than water lilies.

So do the spatterdocks, varieties of Nuphar. These have leaves like water lilies and flowers not bigger than yellow marbles or table-tennis balls. N. advenum is the one usually seen. The flowers are not much to see, but where shade is heavy and you want a pattern of luxuriant foliage to give interest to the surface, the nuphars do better than nothing.

Another good thing about nuphars is that they abide running water and colder water during the summer than water lilies. I am sorry I do not know where nuphars may be bought, but dealers in aquarium supplies and tropical fishes are more likely to sell nuphars (some of which make beautiful membranous leaves under water) than water lily dealers.

In shady pools -- to think of a few positive advantages -- fish show up better. Plain red goldfish are as ornamental as any. Sometimes these can be bought cheap at pet shops where they are sold for animal food.

Otherwise, it is easy enough to order fish by mail from water lily dealers. The fish come in plastic bags.

United Parcel Service managed to take 10 days to ship fish from New Jersey to Washington, and in my last order all but two of the young shubunkins died on the trip. Theoretically, dealers make good on lost fishes, but it can be rather a hassle.

Highly ornamental fishes are the golden orfes, torpedo-shaped or tubular, soft orange in color and usually swimming in formation (they are a shoal fish and do better if there are a dozen or so, to keep each other company) just beneath the surface of the water.

In my experience, at least, they do not flourish in hot weather (that is, they commonly die) when oxygen levels are lower than in winter. They consort with goldfish in a friendly way, but do not abide either stagnant water, or low oxygen levels as well as goldfish.

Among goldfish, if the quite beautiful plain red ones do not seem fancy enough, the streamlined comets, the black bulge-eyed Moors, the Japanese fantails and the multi-colored shubunkins all flourish and winter over well in outdoor pools.

In shady pools algae is not a problem (algae, like almost everything else, flourishes mightily in warm sunny water) and, since water lilies are not going to be grown, you might have a dripping-faucet sort of fountain. Or a mighty jet, for that matter. But both fishes and birds like plop-plop-plop water.

In lily pools I prefer the water to brim right to the top, but some people like the water an inch or so beneath the coping. I go fairly berserk at the sight of plastic liners showing at the top of a pool, but this does not seem to bother most gardeners who use waterproof liners.

Over the years I have concluded it's best to build a pool of poured concrete (as distinct from concrete blocks which I distrust totally, along with bricks, fieldstone, etc., since none of them will ever be free of leaks). If, because you expect to move in a few years, or because you are renting a place, you do not want a concrete pool, I suggest either Fiberglas (in rigid pre-formed pools) or galvanized steel tanks, dutifully scrubbed with vinegar and washed out and prayed over. (Prayers are necessary since the zinc kills fish. In time it weathers and stops killing fish.)

In city gardens, even where space is precious -- and especially where it is most precious -- I would try to have a pool 10 by 12 feet.

Again and again I hear of gardeners who build a 4-by-6-foot pool (or even smaller) and later wish desperately they had made it larger. Usually it is in the only spot available for a pool, so a larger pool would mean tearing out the smaller one, which hardly anybody is bold enough to do. So make it as large as you can the first time.

Sometimes a gardener longs for a pool but can't give the space even for a horse-watering trough, and does not want a mere whiskey barrel with one miniature water lily in it.

It is quite feasible, in such a case, to sink plastic buckets or tubs right in the regular sunny flower border, filled to within an inch of the top with good khevy clay loam. In them you can grow the lovely native pickerel weed, with blue spikes of bloom, or (in the half-barrel) the grand Egyptian papyrus.The earth must be kept saturated.

The papyrus does best with 6 inches of water over its roots in a very sunny spot, but it will do all right without water over it.

You do not want to keep shallow water over such plants in tubs, because of mosquitoes. In a pool, goldfish eat all the mosquitoes, but goldfish cannot survive in a barrel full of papyrus with only a couple inches of water. That is why I suggest soil that is saturated, but without water standing on it.

All these projects, of course, are for the spring, but unless the gardener plans now, he will not get round to anything before hot weather and then will refuse to dig, fool with concrete, etc.