Leeks

Overview

Leeks (Allium porrum or A. ampeloprasum var. porrum), sometimes called “the gourmet’s onion” are related to onions (A. cepa) and garlic (A. sativum), but this species has flat leaves and relatively little bulb development. Leeks are easy to grow and delicious, with a mild onion flavor. The thick leaf bases and slightly developed bulb look like a giant green onion and are eaten as a cooked vegetable. Leeks are not as popular in the United States as in Europe, where they a more common cooking ingredient.

The leek was developed from a wild type, which is thought to be native to Western Asia and the Mediterranean countries. Wild leeks were used as food during the early Bronze Age, around 4,000 BC, and were probably domesticated around 2,000 BC They were part of the diet of those who built the Egyptian pyramids, and Hippocrates.

Leeks have been cultivated in Western Europe since the Middle Ages, and are particularly associated with Wales – dating back to 640 AD when Welsh soldiers wore pieces of leek in their helmets to distinguish themselves from their Saxon foes in battle. The Welsh traditionally wear a leek on St. David’s Day (March 1) to commemorate King Cadawallader’s victory over the Saxons that year. Leeks were brought to North America with early settlers from Europe. Today leeks are grown as an onion substitute and for their own unique mild onion flavor in soups and other dishes.

Leeks have long, strap-like leaves and many develop a roundish bulb.

This plant is a true perennial, even though it is usually grown as an annual. Different varieties vary in their hardiness and ability to overwinter in cold climates. Leek multiplies by means of small lateral growths and often develops a roundish bulb at the base of the main growth. Leeks develop a broad, succulent stem rather than a large bulb like an onion. The plant has a fanlike sheaf of flat, blue-green or yellow-green leaves that may grow a foot or two in length, on a stalk up to 12 inches long. Varieties vary in the length and thickness of the leaf shanks (pseudo-stem).

Wild leek, Allium tricoccum — Wild leek, *Allium tricoccum*

Some plants that are similar to leeks include elephant (or great-headed) garlic (A. ampeloprasum var. ampeloprasum) and wild leek (A. tricoccum). Elephant garlic produces very large bulbs that may weigh a pound or more, and is used as is garlic. Wild leeks, also called ramps, are native to North America and have a strong garlic-onion flavor.

Cultivars of Leeks

There are many named varieties of leeks. They vary from long, green narrow-leaf types with long, slender white stems to long wide-leaf types with thicker, shorter white stems and blue-green leaves. Varieties are often grouped by earliness: early, midseason, and late season. This list includes some of the more common varieties available.

‘Albinstar Baby Leek’ (110 days) is a Dutch variety developed for the baby leek production. Harvestable at ½ inch diameter, but can be allowed to grow larger.
‘American Flag’ (sometimes listed as ‘Broad American Flag’, ‘Broad London’, or ‘Large London’ 130 days) has a mild, sweet, onion-like flavor. The 7 to 9 inch stems blanch snowy white and are topped with blue-green leaves. It is hardy to about 10 °F.
‘Bandit’ (120 days) is a short, mild-flavored leek with very thick shanks with very little bulbing and blue-green leaves. It is very winter hardy and may survive cold winters when protected with a thick layer of organic mulch.
‘Biker’ (90 days) is an early maturing, disease resistant, hybrid variety.
‘Chinook’ (90 to 100 days) is an early maturing, vigorous and uniform, hybrid variety with long shanks.
‘Columbus’ (80 days) is a medium-sized leek that stays long and tall with very little tendency to bulb. The leaves are a blue-green. It has some winter hardiness but benefits from mulching.
‘Comanche’ (105 days) is a hybrid, midseason, long-shanked variety with medium blue-green leaves.
‘Dawn Giant’ (98 days) grows up to 15 inches long and 2 inches in diameter, with blue-green leaves. Can be direct sown in early spring.
‘Defender’ (150 days) is a late maturing hybrid variety with dark green foliage and good rust resistance.
‘Giant Musselburgh’ (sometimes listed as ‘Musselburgh’ or ‘Scotch Flag’, 150 days) is a late season European variety dating back to the 1800s. It features large, tender, white stalks with mild flavor, and medium-dark green tops. A very hardy, dependable variety.
‘Jolant’ (100 days) is a medium-sized variety that can be used for baby leeks or allowed to mature with a 8 to 9 inch long shank. Low frost tolerance.
‘King Richard’ (75 days) is an early maturing variety with long, slender stems that stay tender and white all season long. It can be sown densely to grow mini-leeks for use as a garnish or for soups or salads. It has some frost resistance, and can survive temperatures as low as 20 °F.
‘Lancelot’ (110 days) is a short leek with large, long shank and blue-green leaves. Good cold tolerance.
‘Megaton’ (90 days) is an early maturing, vigorous, uniform hybrid variety.
‘Oslo’ (100 days) is a late maturing hybrid with thick shanks and good uniformity.
‘Pancho’ (80 days) is an early maturing, slow bolting variety good for short season areas.
‘Rally’ (85 days) is an early, hybrid variety with large shanks and resistance to rust and white tip.
‘Tadorna’ (100 days) is a vigorous, reliable variety with dark blue-green leaves and moderate disease resistance.

Leeks are common at farmers markets in the fall.

In the Midwest leeks are best started indoors.

Growing Leeks

Leeks are a cool-season crop and are well suited for cultivation in Wisconsin. They grow best in full sun in well-drained soil. They are a rather long-season crop (80 to 120 days or more). In Wisconsin, it is best to start seeds indoors 4 to 10 weeks before the average date of the last spring frost and transplant the seedlings into the garden.

Sow the seeds thinly and evenly ¼ inch deep in moistened soilless potting mix and cover lightly. Keep the soil temperature at about 70 °F until the seeds germinate. Move the seedlings under grow lights or into a very bright window. Thinning the seedlings will encourage more rapid growth, but it isn’t necessary if you keep them well fertilized.

When the seedlings reach 6 to 7 inches tall, cut them back to 1½ to 2 inches (you can use the part you cut off as you would chives). Harden off the plants before transplanting into the garden starting in late April or early May (the plants will tolerate light frost). You can also transplant later or sow seed directly outdoors for smaller plants. In the southern part of the state, you may be able to successfully overwinter some late-planted varieties in mild winters or with a layer of mulch, but even “winter hardy” varieties may not survive Wisconsin winters.

Planting leeks in the bottom of a trench makes it easy to gradually add soil as they grow to blanch the stems.

In order to grow a large, white leek, the lower part of the stem must be blanched. Blanching can be accomplished by hilling the soil up around the stalk as it develops. Alternatively, seedlings can be planted into a trench 6 to 8 inches deep and the trench gradually filled as the plants grow. In either case, place the young transplants up to the first leaf notch into holes about 6 inches deep (a rake handle is great for making perfect holes). Don’t fill the holes with soil after planting but just water the plants in and let the hole fill up with soil on its own.

Make the holes 6 to 9 inches apart in the garden. If you plant in a double row, stagger the plants with their leaves growing parallel to the rows so they won’t grow into the pathway. For larger plantings, 4 to 6 inch spacing in rows that are 18 to 24 inches apart allows soil to be moved from between the rows around the plants for blanching. Because leeks are relatively slow-growing, they can be interplanted with faster maturing crops such as lettuce. Avoid planting beans or other legumes nearby as the leeks can inhibit their growth.

Midseason fertilization is recommended. In mid-summer, cut off the top half of the leaves to encourage greater stalk growth.

Leeks don’t have many pests, but most insects and diseases that attack onions can also affect leeks. Onion thrips (Thrips tabaci) are quite common, but cause problems mainly under hot, dry conditions. Their feeding produces tiny silvery-white spots on the leaf surface. Onion maggot (Hylemya antiqua) can feed on the plant’s roots, causing wilting and reduced growth. Diseases such as white rot, rust, pink root, purple blotch, downy mildew, botrytis leaf spot, botrytis neck rot, and smudge may occur, but are not common in home gardens.

Leeks can remain in the ground as long as it is not frozen.

Leeks do not go dormant in the fall but continue to grow slowly, so harvest time can be very flexible. Dig leeks any time after they are an inch or more in diameter, but leave them in the ground until you’re ready to use them.

Dig leeks to harvest any time after they are an inch or more in diameter.

You can continue to harvest leeks through a mild winter and into early spring. Put an extra thick layer of mulch around the plants to delay the freezing of the ground and make it easier to dig them up. In a more typical Wisconsin winter, dig the plants before the ground freezes solid. Strip off the dead outer leaves and trim the roots and leaves after digging.

Leeks will keep in a refrigerator for at least a month, but the quality will not be as good as when freshly harvested. The variety and packaging will affect the storage life. Digging the plant up doesn’t stop it’s growth – it will continue to grow (very slowly) for months even under refrigeration but this growth reduces the quality of the stems. Generally only the white part of leeks are consumed.

Author: Susan Mahr, University of Wisconsin—Madison
Reviewers: Allen R. Pyle, Horticulture Outreach Specialist, Bruce Spangenberg, Horticulture Outreach Specialist, UW—Madison Extension
Revised: October 2026