In November and December, between harvesting trips to the garden, leek growers are deciding which varieties to grow next year. Leeks (Allium porrum or A. ampeloprasum porrum) are the easiest to grow of all the alliums. Not only do they perform well in a wide range of climates, they can be harvested at almost any stage for use raw as baby leeks in salads or cooked in soups and sautees.
Their complex onion flavor, though sweet and sharp, is mild enough to be a refreshing relief to breath-conscious diners. They're rarely troubled by pests and diseases and are not finicky about soil fertility and transplanting. And in the garden, they're attractive: Some varieties have blue leaves that contrast strikingly with white stalks, and a few have foliage that deepens to violet after frosts.
Leeks are biennial plants, meaning they're programmed to germinate and grow one season, survive the winter, and then flower and scatter seeds the next season. Most varieties (except those grown for baby leeks) need about 10 to 12 weeks from sowing to reach transplant size, then 12 to 20 weeks in the garden to reach harvest size, depending on the variety and when you wish to use them in the kitchen. You can harvest frost-susceptible varieties in the summer and fall, or leave mulched, frost-tolerant varieties in the garden for winter-long harvests.
They grow best when temperatures are between 55° and 75° F; growth slows at temperatures above 77° F. Some varieties tolerate cold down to 22° to 24° F with no ill effects, and a few even survive temperatures below 0° F if mulched with 12 or more inches of straw. Leeks prefer fertile soil that isn't compacted or poorly drained. Like onions, they don't grow well in soils with little organic matter or in soils that are overly acidic. But the ideal leek soil is the same as for many vegetables-loose, well drained, nutrient- and humus-rich, and with a pH of 6.5.
In northern gardens, the standard and most reliable planting sequence for leeks begins with sowing seeds indoors 12 to 14 weeks before the last frost in your area. Then seedlings are ready to transplant 2 weeks before the last frost. For instance, if you live in Ithaca, New York, or North Platte, Nebraska, where the last frost in spring is usually in the middle of May, sow seeds indoors in mid-February. After 10 to 12 weeks (mid- to late-April), the seedlings should be about the diameter of a pencil and ready to transplant outside.
If you live where the autumns are long and cool and frost is rare (such as in USDA Hardiness Zones 8 through 9a), you can plant two crops. Sow the first crop 12 to 14 weeks before the last frost in spring. In mid-July, sow the second crop indoors. If your area could experience frost during the winter, plant a frost-tolerant variety. After germination in summer, keep seedlings in a cool but bright location until they reach transplant size in late September or early October. Then transplant them outdoors and grow and harvest them through the late fall and winter.
Because leeks prefer cool weather, if you live in zones 9b to 11 where the summers are scorching hot and the winters are mild, sow seeds (indoors) only in July or August to harvest through the late fall and winter. Or harvest after winter in spring if you plant a bolt-resistant variety.
Sow seeds 1/4 to 1/2 inch deep in a lightweight soil mix in flats. If you start leeks in the summer, chill the seeds overnight in the refrigerator before planting. The optimum soil temperature for germination is 52° to 73° F. The seeds should germinate in one or two weeks. Immediately after germination in late winter or early spring, set seedlings on a bright, south- or west-facing window sill, or under fluorescent grow lights. In 10 weeks or so, transplant them.
Set pencil-thick transplants 4 to 6 inches apart in rows that are 12 to 18 inches apart. More space per plant results in fatter leeks, and less space produces thinner ones. Use a dibble or broom handle to make holes that are 6 inches deep, and place one transplant in each hole. Water them in to settle soil around the roots, but don't fill the holes with soil. Let that happen naturally over the season. Planting leeks deep in soil blanches them, shielding the shanks (the portions below the point where the leaves fan out) from the sun and keeping them white, tender, and sweet. Leeks are palatable without blanching, but blanched shanks have better flavor.
A week after transplanting and again halfway through their growing season, give the leeks a nitrogen boost with manure tea or fish emulsion. Throughout the growing season, keep plants well watered. Also keep leeks weed-free, because as with onions, fast-growing weeds stunt the growth of young leeks. Get the weeds when they're small, and you'll avoid damaging the shallow-rooted leeks in the process of uprooting large weeds.
Leeks are ready to harvest whenever they are large enough for your taste. Most leeks can be harvested for use as baby leeks, but some varieties are bred for culinary appeal as baby leeks. In addition, like carrots, frost-tolerant leek varieties taste better after a few frosts.
To avoid damaging the edible portions, use a garden fork to loosen the soil around the leeks first. Stick the fork into the ground parallel and next to the row, and pull down on the handle, forcing the soil to release the leeks. Leave most of the roots intact, and cut the top leaves off in a V shape, with the outside leaves the shortest; this not only neatens their appearance, it slows transpiration that causes limp leeks in the kitchen as well.
If you want to keep leeks through damaging cold periods, harvest and store them in a root cellar. Arrange leeks neck-to-neck, upright, in boxes or crates. Pack moist sand or mulch tightly around the bases. They should last for two to six weeks.
Though all leeks tolerate some frost, some overwinter better than others. Here's a guide to help you decide. Try several varieties in a small garden-the seeds store well for three years if kept cool and dry. In the list, the days to maturity are from transplanting, except where noted.
Good varieties for frost-free regions:
'Otina' (120 days). Long, thick early leeks from France; flavor delicate enough to be eaten raw in salads. Blue-green foliage.
'Titan' (70 days). Dark green leaves. Good for summer and fall harvesting. Very long stalks, early growth, and dark green foliage.
'Varna' (50 to 85 days). Fast-growing, slender, and tall variety grown (often in bunching crops) for baby leeks. Light green leaves.
Good varieties for mild-winter regions: 'Albinstar' (110 days from sowing). Dutch seedsmen developed this one especially for use as baby leeks, so harvest these when they're about 1/2 inch thick for baby leeks, or grow to full size. Deep green leaves.
'Electra' (150 days). Good for summer and fall harvests, but can be overwintered with protection. Dark blue-green foliage and long white stalks.
'King Richard' (75 days). Bolt-resistant. Market gardeners often grow this variety for baby leeks because of fast growth. Tender, tall, and slender stems. Light-green leaves.
'Pancho' (80 days). An early leek that's good for summer and fall harvests. Short, thick stems with deep blue-green foliage.
'Parton' (85 days). The only F1 hybrid leek and new to North America this year. Yields are purportedly 35 percent higher than those of open-pollinated varieties. Long and fast-growing with green leaves.
'Splendid' (95 to 105 days). From Denmark. Long, slender stalks and green foliage.
'Tadorna' (100 days). Medium length, white shaft contrasts sharply with very dark blue-green leaves.
Good varieties for cold-winter regions: 'Arkansas' (108 to 120 days). Bolt-resistant. Dark, blue-green leaves.
'Bleu de Solaise' (105 days). This French heirloom can be overwintered in short-season areas. Leaves are large and blue.
'Durabel' (125 days). Bred to handle winter weather, this Danish variety has milder flavor for use raw and more tender texture than some winter-hardy leeks. Bolt-resistant.
'Giant Musselburgh' (110 days). Popular, large heirloom that also does well in the South. Bolt-resistant. Green fan-shaped leaves.
'Large American Flag' (same as 'American Flag', or 'Broad London') (130 to 140 days). Popular home garden variety producing fat leeks with broad green leaves.
'Laura' (115 days). Extra hardy for fall harvest and overwintering. Dark green leaves on medium-length stalk.
'Longina' (140 days). Adapted to a variety of growing conditions. Long, thick stems and deep blue-green foliage.
'St. Victor' (145 days). New strain selected from 'Bleu de Solaise'. Stores well in the ground, and foliage turns to deep violet as cold increases.
'Winter Giant' (same as 'Alaska') (115 days). With broad, blue-green foliage, a stocky, bolt-resistant heirloom.
Kathryn Khosla is a university horticulture graduate, and at the time of this article, lived in central New York.
Photography by National Gardening Association and Charlie Nardozzi/National Gardening Association