Onion family offers you both color and flavor

There's beauty, a quite exquisite beauty, as well as great flavor in the onion patch. Any grower of chives will confirm this. But right now, I'm thinking of that purely ornamental member of the onion family, the allium. It's an easy grower that adds showy color to the garden for several weeks during late spring.

I want some of that color in my garden next year, so alliums, among the ''glamour bulbs,'' are on my fall planting list. I'm also turning to a new edible variety - new for my garden, that is: The potato onion is an old-time favorite that is being rediscovered by home gardeners.

Alliums - or ornamental onions, as they are often called - come in one shape, but in a variety of sizes. The allium flower looks like a fluffy pompon (some say it reminds them of cotton candy) on the end of a stick. Actually the flower is made up of hundreds of tiny florets radiating from a central core. The principle color is lilac, but some varieties produce pink, yellow, and white flowers.

Unlike the edible onion, alliums give off no oniony smell unless the plant is bruised. The ''lonely little petunia'' wouldn't cry in this company. Shorter allium varieties are a sought-after rock-garden flower; larger varieties look good in borders and among shrubs.

Allium karataviensem is one of the shorter varieties. Sturdy stems, about 8 inches long, support silvery-pink or rose-colored florets that appear in May and last for several weeks. The broad, gray-purple leaves grow close to the ground.

At the other end of the scale, Allium giganteumm produces softballsize blooms on the end of stems 4- to 5-feet high. Allium aflatunensem produces lilac, pink, or purple blossoms on 3-feet-tall stems.

Alliums are independant plants. They demand little from the gardener except a well-drained soil and full sun or partial shade. Plant the bulbs 8 inches deep and 6 inches apart, throwing a handful of bone meal in the planting hole. Thereafter, bone meal sprinkled between the plants each fall is about all they need to keep them going for years.

Once established, alliums spread freely, as do daffodils. Dig them up and replant when overcrowding begins to reduce the number of blooms.

The potato onion is believed to have originated in Ireland, later spreading to England and then to much of Europe. The Scandinavians, in particular, appreciated the versatile multiplier onion. It is, by the way, closely related to the shallot, which is so much a part of French cuisine.

In the 1800s, the potato onion was an important commercial onion here in the United States, as well as a back-yard favorite. A seed catalog of the day described it as: ''Early, very productive, mild flavor, and the most profitable variety grown for market. . . . Equally adapted to be sold green as bunch onions or as fully matured large onions.''

As a multiplier, the potato onion is best propagated by sets - by planting onion bulbs, in other words. Larger onions divide after planting to produce a host of green bunching onions (or next season's sets, if you wish) while the small onion will develop into a large one, about 3 inches in diameter, by the end of the year.

Another plus for the home gardener is how easily the onions store - up to 12 months in a cool, dry space.

In most regions (the bulbs are hardy down to minus 25 degrees F.) the potato onion can be planted in the fall, given a good protective mulch. The idea is to plant a mixture of sizes - small to provide you with large storage onions, and large to provide green onions for eating and sets for planting. A Virginian gardener reportedly plants a bushel of sets each year and harvests, on average, 14 bushels of mature onions.

A soil rich in organic matter, a sunny location, and regular waterings during dry spells is all the potato onion requires to do well.

Commercial suppliers of potato-onion sets are not as common as they once were. One source I am aware of is: Kalmia, PO Box 3881, Charlottesville, Va. 22903.