Vegetable · Amaryllidaceae
Leek
Allium ampeloprasum
Plant them deep, feed them hard, and hill the soil up, and a leek hands you a long sweet shank that stands through the cold.
Full sun
Every 3–7 days
120–150 days
USDA 5–10
Overview
The leek is the onion family's most patient member, and it never troubles itself with a bulb. What reaches the kitchen is the shank, a long cylinder of tightly wrapped leaf bases blanched white by deep planting and by mounding soil up the stem through the season. Its flavor is gentler and sweeter than an onion, the sort that softens into soups and braises and holds its poise through cooking.
This is a crop for the gardener who enjoys a slow arc to the year. Leeks want 120 to 150 days to mature, so most begin with seed indoors in late winter and set pencil-thick seedlings out around the last frost. The reward is a vegetable that keeps its place in the bed for weeks and, tucked under mulch as a hardy variety, carries fresh flavor right into the depths of winter.
Offer a leek deep, rich soil, steady water, and generous feeding, and it grows slow and strong into the fat white stem the kitchen wants. Crowd it, underfeed it, or let the bed run dry, and you are left with thin, tough shanks that never quite earn their place at the table.
Care
The short version: full sun, deep and fertile soil, and steady moisture from spring to harvest. Set the seedlings deep, hill soil up the shank to blanch it white, and feed on a regular rhythm, since leeks are generous feeders that repay the effort at the table.
Light
Leeks favor full sun to build a proper shank, though they will accept a little afternoon shade in a warmer garden. Give them too little and the shanks stay thin while the plants grow slack and unruly.
Water
Keep the bed evenly moist and never let it dry out fully, or the shanks turn thin and tough at the table. Aim for about 1 inch (2.5 cm) of water a week for the shallow roots, and let a layer of mulch carry the moisture between waterings.
Soil
Plant into a deep, loose, fertile loam enriched with compost or aged manure, which gives the long roots their run and feeds a hungry crop through the season. A pH between 6.0 and 7.0 suits them handsomely.
Temperature
Leeks are remarkably hardy, taking anything from 14°F to 86°F (-10°C to 30°C), and a touch of frost only sweetens the shank for the kitchen. Heat is the harder guest, since hot, dry spells wear the plants down and open the door to thrips.
Humidity
Ordinary outdoor humidity is all the crop asks, so there is no figure to chase. What truly matters is airflow, because crowded, damp leaves are exactly where leek rust likes to make its entrance.
Feeding
Leeks are hungry feeders that want a steady table all season. Side-dress with a nitrogen-rich or balanced fertilizer about once a month from spring through late summer while the shanks are building.
Pruning
Trim the seedling tops back to about 4 to 5 inches (10 to 13 cm) once or twice before transplanting, and the plants set out sturdier for it. Should one begin to bolt, lift the flower stalk out quickly, since a bolted shank turns woody.
Repotting
not applicable; grown in open ground (or a deep container) for a single long season and harvested
Size & spacing
Plants stand 12 to 35 inches (30 to 90 cm) tall on a slender footing of just 4 to 6 inches (10 to 15 cm). Give each one room so air moves freely and the shanks fill out without crowding their neighbors.
When to plant
Leeks keep a long, gracious calendar that favors an early start. Sow indoors in late winter, set the seedlings out around your last frost once they are pencil-thick, then gather them from late summer through fall and, with a hardy variety under mulch, well into winter.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: 8-12 weeks before the last spring frost
- Plant: around the last frost date, once seedlings are pencil-thick; set them deep in dibble holes or a trench and hill soil up as they grow to blanch the shank
- Harvest: harvest from late summer through fall and, for hardy cultivars under mulch, into winter; flowers only in the second year if overwintered
Hardiness
USDA hardiness zones: 5–10
Temperature: down to -29°C
Troubleshooting
Most leek trouble reveals itself on the leaves or in slim shanks that never fill out. Notice the signs early and you can usually set the crop right before harvest. Match what you see below, then act while the season still favors a fix.
An early flower stalk and a hardening shank
When a leek raises a firm, round flower stalk in its first year, it has bolted, usually after a long cold spell fooled a large transplant into believing a winter had come and gone. Drought or the shock of transplanting can hasten it as well. From here the eating quality only slips, so bring those plants to the kitchen first and enjoy them before the rest.
Fix:
- Harvest bolted plants immediately and use them; quality only declines
- Snap out very young stalks and use those plants first
Orange streaks marking the leaves
This is leek rust, a fungus that settles in during humid stretches and wherever the rows are packed shoulder to shoulder. Lift away the worst leaves, give the planting the breathing room it wants, and lighten the nitrogen that pushes the soft growth rust prefers. A patient rotation of alliums on a 3 to 4 year cycle keeps the spores from lingering in the bed to trouble next season's crop.
Fix:
- Remove and destroy heavily infected leaves
- Thin or widen spacing to improve airflow
- Avoid overhead watering late in the day
A silvery, grayed look across the foliage
That silvered, pewter cast is the calling card of onion thrips, small insects that scrape the leaf surface and multiply through hot, dry weeks. A parched bed suffers most, so steady watering and a good mulch keep the planting composed, while a firm spray of water sends the thrips packing. When the pressure mounts, a little insecticidal soap worked into the inner leaf folds finishes the job.
Fix:
- Knock thrips back with strong jets of water
- Keep plants well watered and mulched
- Use insecticidal soap on the inner leaf folds if pressure is heavy
Shanks that stay slender rather than filling out
Slim, pencil-like shanks are usually the mark of a crowded bed, a late start, or soil that ran short on richness. Leeks take the full 120 to 150 days and feed the whole while, so thin the stand, clear the weeds, side-dress with nitrogen, and water deep and even. There is no need to hurry the harvest, since leeks keep beautifully for weeks in cool soil and the smaller plants go on gaining girth as you wait.
Fix:
- Thin to proper spacing and weed thoroughly
- Side-dress with nitrogen and water deeply and evenly
- Leave undersized plants in the ground longer; leeks hold well in cool soil
Toxicity
Leeks are a pleasure at the table and a genuine hazard to animals, a line worth keeping in mind at home. Like every allium, they carry organosulfur compounds that break down red blood cells and cause hemolytic anemia in pets and livestock, cooked or raw. Keep the growing plants, kitchen trimmings, and compost scraps well away from cats, dogs, horses, and grazing animals, remembering that cats are the most sensitive and the signs can be days in coming.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Severe
Cats are the most vulnerable guests in any home, and even a small nibble can turn serious. The early signs are vomiting, drooling, weakness, and pale gums, giving way to rapid breathing and red or brown urine as the red blood cells break down into Heinz-body hemolytic anemia.
Dogs Moderate
A dog that gets hold of any part of a leek may come down with vomiting, diarrhea, belly pain, and a slow slide into weakness. A larger or repeated helping carries it into the same hemolytic anemia, with pale gums, a racing heart, and dark urine.
Horses Moderate
A horse that grazes a real quantity of leek grows dull and weak, with pale or yellow-tinged gums and dark urine as the blood cells give way.
Rabbits Toxic
Leeks and every other allium are entirely off the menu for rabbits. The same organosulfur compounds attack their red blood cells, so keep all parts well away from the hutch.
Livestock Toxic
Cattle, sheep, and goats are all at risk, and the harm can accumulate through grazing alliums over time. Expect weakness, pale gums, and dark urine as anemia sets in.
Birds Toxic
Birds, backyard hens among them, should never be offered leek scraps. The toxin damages their blood cells just as it does in mammals.
People Safe
For people, leeks are a kitchen mainstay and perfectly safe to grow, handle, and cook. The only note of care is the cleanup: keep trimmings and compost scraps where pets can't reach them.
Safe for people to grow and handle; keep growing plants, kitchen trimmings, and compost scraps out of reach of pets. Onset of anemia signs in pets can be delayed by several days after ingestion.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
United Kingdom
Animal PoisonLine: 01202 509000 (fee applies)
Australia
Animal Poisons Helpline: 1300 869 738
Varieties
Leeks fall largely into early types for the fall table and hardy late types bred to stand through winter. These are the names worth carrying to the seed rack.
King Richard
An early leek with long, slender shanks made for the fall table, though it counts among the least winter-hardy of the group.
American Flag (Broad London)
A time-honored open-pollinated heirloom loved for thick shanks and the cold tolerance that lets it stand through to spring.
Bandit
A very hardy late leek dressed in dark blue-green leaves, bred to hold in the ground all winter for fresh cold-season harvests.
Lancelot
A trim, upright mid-season hybrid whose long white shanks come to the sink clean and ready.
Companions
Leeks pair well with crops that swap pest protection and share their need for rich, moist soil, and badly with the legumes that alliums tend to hold back.
Plant near
carrot: Classic pairing: leeks are reputed to deter carrot rust fly while carrots help deter leek moth, and the crops share bed conditions without competing strongly
celery: Similar needs for rich soil and steady moisture make celery a compatible bed partner that uses the space between slow-growing leeks
Keep apart
beans: Alliums are traditionally reported to inhibit the growth of beans and other legumes when interplanted
peas: Like beans, peas are reported to grow poorly alongside Alliums and should be kept in a separate bed
How to propagate
There is a single path to a leek, from seed, and the whole art lies in starting early enough and planting deep enough to blanch a long white shank.
SeedModerate
Sow indoors 8-12 weeks before the last spring frost; transplant outdoors around the last frost date · Germinates in about 1-2 weeks at 18-24°C (65-75°F); reaches transplant size in 8-12 weeks
Leeks come from seed alone, and the long lead time is part of their quiet charm. Sow indoors 8 to 12 weeks before the last frost, where the seed rises in a week or two at 65°F to 75°F (18°C to 24°C) and then eases its way toward transplant size. Once the seedlings reach pencil thickness, settle them 6 inches (15 cm) deep in dibble holes or a trench, water them in without firming the soil, and go on hilling soil up the stem all season to blanch a long, sweet white shank for the kitchen.
Myths
Leeks form a bulb like onions and are ready when the tops fall over.
A leek never forms a true bulb at all. The white shank you cook is a cylinder of tightly bundled leaf bases, blanched pale by deep planting and by mounding soil up the stem. Read the harvest from the size of the shank, never from the tops flopping over.
Cooked leeks are safe to share with cats and dogs.
Cooking, drying, or grinding a leek to powder leaves the organosulfur compounds in an allium untouched. A cooked leek is every bit as dangerous as a raw one, and cats can develop Heinz-body hemolytic anemia from remarkably little.