THE DAYLILY continues its triumphant progress as the main flower of the summer simply because it has no rivals.

From early June to late August (with a few stragglers after that) it goes on filling the place with bloom, but today we should think what is possible in small city gardens, not in big places where they can have 600 clumps of day lilies.

It amazes me that people expect miracles from garden plants. People say, "Oh yes, I planted daylilies but they only bloomed a few weeks" and then shut up shop for the rest of the year.

When gardeners say "daylilies bloom all summer," they mean that some flowers will appear over those months provided early and late varieties are included. No daylily, and no other flower, will bloom at a picture-book peak for week after week.

Each clump will look good perhaps three weeks - it depends on the variety - and then you must count on later varieties that, needless to say, were not flowering when the early clump was.

This elementary truth may be osbcured in a garden devoted largely to daylilies. For there you will see a good show of bloom week after week, simply because there are hundreds of plants.

The first thing to do, in a smaller garden, is to decide how many daylilies can be squeezed in. If I had one of those 20-foot square gardens in town, I might settle for two good clumps, say 'Golden Chimes' for a mass of yellow-gold (getting on toward orange) for three weeks starting in late June, and "Iffy" for a less concentrated, but more prolonged, display of pink later on.

The varieties would not make much difference, as long as they were kinds that made the gardener register at least 8 on a happiness scale of 10.

Here is another great point - if the gardener likes small lemon-yellow flowers best of all, there is no conceivable point in planting other colors and sizes.

One of the popular daylilies of the moment is 'Winning Ways,' a soft but full yellow. Some people, however, simply do not like its looks and obviously they should grow something else. (I like it enormously but these things are all subjective.)

There are small reds and big reds, orange-bolds and creamy primroses, buff yellows and green yellows, apricots and rasberry roses, canteloupes and corals, baby-ribbon pinks and ivories overlaid with orchid pink.

In a small garden you will remember that you want the garden to look good in late September, in January, and don't forget how eagerly you peer about for signs of flowers in February and March.

Remember how you admire peonies, irises and roses together (all of them great occupiers of space) before the daylilies bloom, andremember how painful October is without bronze chrysanthemums.

There is also the matter of lilies and tuberoses and if you are struck dumb by dahlias you must remember they take worlds of room.

Apart from flowers, there must be space for box and yew and junipers, space for gracious vines like honey-suckle and clematis, and certainly there should be a place in the sun for a little pool where some fishes may swim and beside which the gardener may laugh at lesser contentments.

All of which cuts down on the space available for daylilies.

I myself think in terms of bean baskets, which can be set here and there to give an idea of the amount of space needed for each daylily clump. Sometimes I cheat a little.

The National Arboretum has a daylily display garden which for the next month or so should be very pretty - usually early July finds the greatest show of bloom.

Daylilies have few ailments. Sometimes they have thrips, which disfigure the blooms. For some reason my clump of 'Cloud Dancer' often has thrips but nearby clumps are not bothered. I do not spray, preferring to growl at 'Cloud Dancer' every year. This may be the place to say many daylilies have names I deplore, and such things as 'Precious One' are best called 'That Pink'.

Do not, if you want my suggestion, be seduced by too many canteloupe colors, which are exciting and beautiful, but which do not show up as well as the sharp yellows. Also it is well to resist the reds, which are irresistable, since they too are gorgeous but not as brilliant in the garden as you think.

It is said old men like yellow best, because that is the color that registers best on old eyes. This may be true.

A final thing, do not imagine daylilies will grow in deep shade. They will survive but not bloom well in deep woodland. They should have four hours of sun a day. Sometimes I cheat, as I also cheat with sun for water lilies.

Soil should be deeply dug, say 18 inches if the back holds out, and it should be good, as if you were going to plant irises or peonies. You should also arrange a water supply, so that from late May onward into the blooming season they can be soaked if the heavens fail.

It is true that daylilies grow so dense that few weeds appear if the clumps are set 30 inches (or even 24) apart. They can be planted any time now through early September.