PHLOX IS a troublesome and worthwhile creature of the Washington garden. Troublesome, because it requires ordinary good culture and ordinary sun, and many town gardeners provide neither.

The great terror of the phlox is the eelworm.It is sai, on high authority, that if cuttings are taken (stem cuttings, not root cuttings) every couple of years, clean plants can be grown that will give no trouble.

Once I acquired about 15 varieties of phlox, in assorted colors from white through pink, rose, scarlet, orage, lavender, deep purple and white, and ran into eelworm trouble sooner than seemed fair.

I now have only a clump or two of the scarlet 'Starfire,' one of the standard and good reds. A friend of mine has wound up with 'Dodo Hanbury Forbes,' one of the standard good pinks.

But the main trouble, as I have observed trouble, is not the eelworm, which can readily enough be bypassed by occasional propagation from cuttings, but lack of sunlight and weeds.

In theory, I know people do not have weeds. But I cannot help noticing that many gardeners, by the end of June, have quite given out, as far as weeding is concerned, and this is a terrible error as far as phlox are concerned. They really do not like what I call July Clutter, that fringe or wave of weeds that only come into strength and power in July and August.

I have much trouble with pokeweed, a handsome enough plant that some people eat in the spring, like asparagus, but which in general is quite poisonous and is best avoided, at least on my table.

Birds eat the berries (which are also said to be poisonous and I do not propose to test them) and my small garden is known to birds of 24 states as the ideal site for digesting and evacuating pokeweed seeds. These sprout very delicately and sometimes sit only three or four inches high the first summer, dying back in November. The next summer they reap the rewards of having established their roots. They can shoot up to 10 feet high, more usually seven, with a stem sometimes as thick as a wrist.

They are rather tropical in appearance, and the long clusters of purple berries (said to make an excellent ink; certainly they make a conspicuous stain) are beautiful.

Every winter or spring I dig up a certain number of pokeweed roots, some of them as large as a watermelon.

Anyway, neither phlox nor any other garden plant can stand their competition.

Various hot-weather grasses also begin to flourish in July; things like crab grass and goose grass. These grow with unbelievable vigor after a period of sitting there looking innocent, no larger than a quarter. The seeds are scattered here and there and they germinate about an eighth of an inch from the stem of some favorite plant, where they are not noticed.

Often the first sign is a lavish extension 14 inches to the side. When pulled up -- they come up very easily -- the phlox or whatever was there is much disturbed.

Clean cultivation is best for phlox. Gardeners who never have noxious weeds should enjoy things like phlox. But those who know perfectly well that July is going to get ahead of them, and that August is going to leave them prostrate, may as well save money and effort and forget phlox and most other things.

This summer, in which we have had some truly fine hot days, that we all regard as a major blessing of life, has been about as perfect as a Washington summer ever gets. For often we lack the heat and sun we are entitled to, and I think we all suffer in those relatively chilly seasons. a

But this summer has not been chilly, at least not since June got well under way. As a result, a number of plants were shocked. I have a willow growing in a tub that dropped every leaf, though it is several years old and about 10 feet high. Even though it was watered faithfully in its tub, its root system was (I believe) too small to support the water loss from the leaves during the great (and most welcome) heats.

It has now sent not new leaves along its stems, though possibly the tips of the branches will die back.

This phenomenon may also be observed on some clematis, which have turned quite brown. Faithful watering will usually inspire them to put out new growth.

One plant that I grow out of sheer perversity is Rhodendron (Azalea) schlippenbachii , an Asian deciduous azalea from the Diamond Mountains of Korea. It seems to me it should grow to perfection with us here, since woody shrubs from Continental Asia (as distinct from the warm subtropical coastal areas) find here a climate much like home.

And yet this azalea with me sits there. It makes enormous leaves, for an azalea, and from time to time I feel I have given it too rich fare, until I reflect I have not fertilized it at all, and Clematis tangutica, another Asian, has never shown the least sign of being especially happy or well-fed.

Anyway, the azalea has a bad habit of showing annoyance with heat and drought by dropping its leaves, especially in late August. Since they are supposed to color in the fall, this is exasperating, and it is also alarming, since you are not sure the plant is still alive. I have, therefore, taken to watching it from mid-July on, to make sure it does not get dry.

The azalea appreciates this. It does not appreciate it enough to flower in the spring, however. Since everybody knows this is one of the most beautiful and showy of all wild azaleas, and since it is said to like sun (which I give it) it is highly annoying for it not to flower.

Several gardeners tell me they have the same luck with it. I suppose some day we shall hear it likes total darkness and a soppy soil, or some such heresy. Certainly it does not respond very well to conditions regard as ideal for it.

Though gardeners should be modest.Sometimes we simply do not know what a particular plant likes, and sometimes an individual plant surprises us by refusing to flourish in "ideal" sites, only to grow admirably elsewhere.

Once I had a common garden iris years ago, 'Cream Chiffon,' that flourished in an ill-drained boggy site in more than half shade. No other iris would grow in that part, and 'Cream Chiffon' never flourished for me in the regular border in which all the other common irises grew like mad.

And yet in other people's gardens, I used to see this same iris growing with the rest, in nice sunny dry sandy loams. I never understood it, but did not argue, since I liked it well enough the way thing were. But you do wonder.

Wonder, not to mention general bafflement, is probably good for gardeners, and reminds us we do not really know as much as we sometimes think we do.