AZALEAS AND wildflowers are the great features of the Landon Azalea Garden Festival from 10 a.m. to 6 p.m. on April 28-30.

In the 25 years that the Landon School has held this public azalea display at the height of their blooming season, it has become one of the pleasantest and least traumatic rites of spring for capital gardeners.

The 72-acre school grounds at 6101 Wilson Lane, Bethesda, will be open without admission fee. The 2 1/2-acre formal garden is stuffed with azaleas, rhododendrons, three peonies and wildflowers.

To benefit a scholarship fund a sale of plants has become a looked-for attraction of the festival. Azaleas are rooted from cuttings - Kurumes, Glenn Dales, Exburys' and so forth - some of them hard to find at nurseries.

A group of the Lower School boys will sell herbs - lavender, rosemary, etc. - for the kitchen and the ornamental garden both. What this town needs, by the way, is a rosemary that doesn't drop dead will in the winter. I have finally concluded rosemary needs a wall at its back and a good light soil with plenty of sand.

Various andromedas and other flowering shrubs will be sold and, for those who must think of their bellies, as if the flowers were not enough, there will be a bake shop, shrimp salad sandwiches and other sinful things.

The glee club will sing, and the visiting gardener can either sit down to let Purcell repair his soul or else get on with the tours of the nature trail or examine the sale of rose bushes, bedding plants, vegetable seedlings, etc.

The Wildflower Garden produces about 3,000 plants for sale - rue anemones, bloodroot, Virginia bluebells, butterfly weed, blue phlox, lady slippers and the like.

Needless to say these are propagated by seed or division or cutting, not scrounged from the wild. Some of the wildflowers are bought from nurseries and resold.

Red and yellow barrenworts (Epimedium) are not to be found on every street corner, and I hope they sell well. The yellow one in particular is ideal for dappled woodsy town gardens, having the constitution of a weed, the restraint of gardens, having the constitution of a weed, the restraint of a lady, and the admirable combination of superb foliage (somewhat like a meadow rue or columbine) plus wiry stems of delicate flowers in April, as enchanting as orchids. How admirably they flourish in front of azaleas under oaks and maples.

The uncommon Jeffersonia will be for sale, a modest little twin-flowered creature; the sturdy, discreet and somewhat infiltrating Mitchella; the soldiers and sailors (Pulmonaria saccharata) with soft spotted leaves and clusters of tubular flowers that turn from pink to blue.

It is always a pleasure in March to find them snuggling about the edge of some clump of early daffodils. The spring beauties (Claytonia virginiana) are not much in the individual pinkish flower, but if happy will make patches 100 feet wide in a sunny lawn of Bermuda grass on land not too light and not too dry.

There will be trilliums, of course. I have always been glad. I escaped the passion for trilliums, though it is pleasant to see them, always, in woodsy places. I used to grow the big white ones smack up against the trunk of an elm in a ferociously dry spot, and they flourished; but of course they like a damp woodland site rich in decayed leaves.

The uncommon shooting star (Dodecatheon) and the commoner, but eminently desirable, solomon seals will be available, and a number of violets plus sweet woodruff, pasqueflower and much else.