THE JAPANESE irises now blooming are opulent beyond almost any other flower, but they are not showy in the garden and you have to gaze at them as individuals to enjoy them.

Often I fidget in my head to think of flowers suitable for small town gardens, which are mainly brick with a couple of chairs and a few treasured plants, and I thought the Japanese irises might do.

So 13 months ago I got a packet of seeds from Park's and resolved to tell you how they turned out.

Everybody in Washington knows those 25-gallon half-barrels of oak that used to hold whiskey. They are about 24 inches wide and maybe 18 inches deep.

I got one and filled it with fairly good ordinary garden dirt to within two inches of the top. There are no holes in the bottom for drainage, and I did not drill any, because I wanted something that stayed on the soggy-boggy side.

The iris seeds planted in May all came up like radishes in a few days; and I planted about 24 of them in the barrel, giving them their permanent positions when they were about two inches high. Usually one plants the seeds outdoors in October and they emerge in April.

During the summer I kept them watered - a bucket or so every week, perhaps - and pulled the tiny weeds out as they appeared, but in very short time the irises grew large enough to prevent any new weeds from emerging.

By fall the irises were maybe 15 inches tall, and two or three fans of leaves had formed for each little plant. About Christmas time I gave them a two-inch mulch of horse manure.

The leaves all died down into a colorless much for the winter, but in spring they began to grow strongly; and the iris flowers started appearing the end of the first week in June.

You will understand that 24 clumps (for each plant has about four sheaves of leaves now) of iris in a tub only 24 inches in diameter is more than enough, and I was not sure they would bloom very well when so crowded.

From April on, I kept the tub soaked. Virtually every plant has produced flower stalks; and while the flowers are not as large as they would be if given more space, still they are bigger than the palm of my hand - and that is big enough.

I began to notice 20 years ago that no matter what the books and specialists sometimes say, there is much of a muchness about Japanese irises.

I used to buy named varieties with such impressive stylings as 'Moon Over the Tortoise Cat's Ear' and 'Shimmering Brocade of July Charcoal Pit' and so on, though I forget them exactly, and they were nice enough.

Then one day I was in a garden where they had raised the irises from seed and I said, "Ha, you have 'Glory of Titmouse Nest' doing extremely well," and they said, "Oh no, they are just a batch from seed."

Well. I saw that my named varieties at $10 each were not any better than theirs from seed that cost less than a penny.

In theory, the fine named sorts have greater substance, better poise, etc.

In my experience, however, none of them stands up to wind or heat or rain very well - you would not really expect it in a flower as large and flat as a pancake.

It is a good idea, needless to say, to get good seeds to begin with, and I have been utterly pleased with what I got, called the Higo Strain. I think I paid 75 cents for them.

Today there are six plants in bloom, all different. One is milky white with a flush of blue. Another is solid white except for a flush of yellow. One is pale blue with dark blue veins and a violet center. One is a pale lilac-rose with a touch of yellow, and another is rich mulberry with some white veins, and one is violet-blue with black veins and a central boss of red-purple.

These are standard colors and patterns in Japanese irises, and nothing in the vegetable kingdom is richer, more luxurious, or even more noble than these flowers. The three great broad almost circular petals are flat, drooping a bit at the edges, with three small upright petals in the center. At the center, and extending variously on to the petals, are three little flashes of yellow.

There are only two flower buds on a stalk, and the second one flowers a few days after the first. I suppose the tub will have flowers for three weeks.

Some bloom only 18 or 20 inches above the earth, while others are three or four feet tall. The foliage, like very narrow swords, is completely upright, and from a distance you think they are some attractive neat water rush.

In Japan they sometimes grow these irises in individual pots, which are set in shallow pools a few weeks before blooming. Another thing they do is grow the irises in rows like vegetables and by means of little dikes they flood the bed in the spring, keeping a couple of inches of water standing over the plants till after flowering, when they let the water off.

Yet again they grow the irises in large clumps in fish pools (the water only two to four inches over the crowns) so that when the irises are in bloom you can watch the colored fishes swimming among them.

These irises grow and bloom perfectly well in oridinary garden borders in the sort of site you would give a tomato plant or a rose bush, and I have grown good ones without giving them any supplemental water at any time during the year.

It is important to keep lime away from them. Our natural soil, so strongly acid that we need not do anything at all to grow fine azaleas and rhododendrons, suits them perfectly.

They are gross feeders, as the books say, meaning simply that they appreciate mulches of rotted manure. I used fresh horse manure in December, and it did well. Ordinary chemical fertilizers of common formula (5-10-5 and so on) will do well, but the plants will die with wonderful speed if anything alkaline gets near them.

On a sunny terrace I think these irises in a half-barrel justify their space. Even apart from the gorgeous flowers, the foliage is pleasant and vigorous in itself.

The color range, you will notice, is white through mulberry and deep violet. The "blue" ones are not especially blue and there are no yellow.

These irises will never make a flamboyant mass of color like the tall bearded irises. Even if the Japanese iris colors were brilliant - and they are not brilliant at all, but subdued and rich and soft - they are not produced in masses.

Needless to say, they will never produce the color in a tub that is so easily provided by geraniums, petunias, lantanas fuchsias and so on. And you have the flowers three weeks instead of 4 1/2 months. So they are no flower for those who want a blob of gorgeous color in an otherwise leafy green and paved town garden.

Maybe if there is room for only one tub, then the annuals mentioned (puls verbenas, nicotianas, heliotrope, snap-dragons) would give more pleasure during their very long flowering season. But often there could be several tubs, and the Japanese irises would not only contrast with the bright annuals, their distinguished foliage giving greater dignity to the tumbling petunias, but would provide in their brief season of flower something to look forward to, more than the ceaseless geraniums. CAPTION: Picture, no caption, Tokyo National Museum/UNICEF