The Life of the Leek

Q. Some of my leeks were too small to harvest so I left them in the ground last year, and now they are about to flower. Will they still be good to eat after flowering? I don't want to harvest them now. I want to enjoy the flowers, but it would be nice if I could eat them afterward.

A. Just remember how much you enjoyed those alliumlike flowers when you harvest and eat what remains of the leeks. As a biennial, leeks, members of the same family as onions, shallots and chives, have their own agenda. They spend the first growing season stocking up on energy and storing food in their underground storage bin -- the part of the leek that we eat. By harvesting in the first fall, you are the beneficiary of the leek's efforts. If you wait until after flowering, during the second growing season, the leek is the beneficiary. It uses up that energy as the plant devotes everything to setting seed before it dies.

As its second spring arrives, the leek begins to create its flower stalk. To support the flower, the center of the edible portion becomes woody and inedible. Taking energy from storage to produce a flower reduces the size of the leek and gives it a sharper flavor. The best tasting overwintered leeks are harvested early in the spring.

Not all leeks are winter hardy, so if you intend to leave your leeks in the ground to overwinter, choose a hardy variety like Bleu Solaise, Siegfried or Laura, and mulch them after the ground freezes.

Sources for winter-hardy leeks include Fedco Seeds, P.O. Box 520, Waterville, Me. 04903, (207) 873-7333 (for free catalogue; no phone orders), and Cook's Garden, P.O. Box 5010, Hodges S.C. 29653, (800) 457-9703, free catalogue.

Hardiness Zones

Q. Garden books often give numbered climate zones for perennials and trees. How strictly do I have to follow these numbers? If I live in Zone 5 (the lower Catskill region of New York State), can I try something listed as Zone 6? Do all writers agree on the zones for these plants, or is there some doubt I can benefit from?

A. Hardiness zones, geographic regions classified by averages of the lowest winter temperature that an area will normally reach, have been used as a guide to choosing perennials, trees, shrubs and ground covers since the first zone map was published in 1927 by Alfred Rehder of the Arnold Arboretum of Harvard University. The idea has continued to be refined, and the latest version, published by the Agriculture Department, goes from Zone 1 (temperatures regularly falling below minus 50 degrees) to Zone 11 (never falling below 40 degrees). Each zone represents a 10-degree difference, and each is further divided into A and B zones of 5-degree increments, with the A's cooler than the B's.

Winter-hardiness information is sometimes not foolproof when an area's growing conditions vary widely. In the 1954 edition of its ''Western Garden Book,'' Sunset Publishing divided the Western and Pacific Coast states into 24 zones, taking into account summer high temperatures, humidity, rainfall, elevation, latitude, the influence of the ocean and other characteristics.

But no matter how many divisions are made, the general conditions may be different from the actual conditions in the microclimate of a spot in your yard. Microclimates depend on elevation, openness to the wind, surrounding sheltering material and available moisture, among other things that can effect temperature at any moment. You may live in a region that is generally Zone 5, but some parts of your garden may be a bit warmer or cooler than others, though probably not by a whole zone.

And, of course, averages can be misleading. Borderline plants may do fine for years and then get wiped out by one of those winters that hark back to childhood.

Experts differ on assigning hardiness zones to plants, but then individual plants and individual test sites also differ. Just as you can move from doctor to doctor until you find a diagnosis you agree with, if you look in enough books, you might find one where the plant you are interested in is listed as Zone 5, instead of Zone 6. Whether or not you want to take the risk against the advice of the majority is up to you. As long as you're not my stockbroker.

Address questions to Garden Q.& A., The New York Times, 229 West 43d Street, New York 10036, or by E-mail to gardening@nytimes .com. Those of general interest will be published. Unpublished questions cannot be answered individually.

Drawing FLOWERING LEEK -- In the second growing season, the plant has its own agenda. (Joanna Roy)