Leek

Leeks (Allium ampeloprasum) are a 4-month crop with one significant advantage: once they’re sized up, they hold in the ground through heavy frost without degrading. A fall leek harvest runs from September through December in most of the country - or through February in zones 6 and warmer with cold-hardy varieties. That’s a fresh vegetable at $3.50-$5.00/lb during a period when most beds are empty, and no storage required beyond leaving them in the soil.

What you’re actually growing

Allium ampeloprasum is in the same genus as garlic and chives, though it’s more closely related to the wild Mediterranean leek than to common onion (A. cepa). It forms a tall, blanched shank rather than a bulb. The edible portion is the white and pale-green lower shank, produced by excluding light as the plant develops.

Leek varieties divide broadly by season:

Summer/fall types (like ‘King Richard’) mature in 75-90 days, have long shanks but limited cold hardiness - good for fall harvest before hard frost. They won’t reliably overwinter in zone 6 and colder.

Winter/overwintering types (like ‘Bandit’, ‘Giant Musselburgh’, ‘Jaune du Poiteau’) have shorter, thicker shanks and survive temperatures to 10-15°F without protection. These are the varieties for late fall and early spring harvest and are the ones worth growing in the northern half of the country.

The distinction matters. If you’re planting for fall harvest only, summer types work. If you want leeks in November through February, grow a winter variety.

The ROI case

Leeks at retail run $3.00-$5.00/lb based on USDA AMS terminal market vegetable price data. Your 0.75 lb average yield per plant at $3.50/lb returns $2.63 per plant. At 6 inches spacing in a 4-foot row, you can fit 8 plants and return $21.00 in grocery value against a $2.99 seed cost. The per-plant seed cost is about $0.05 once you factor the packet yield.

The timing advantage compounds the economics. Leeks occupy bed space through the shoulder season - you can transplant out from nursery starts after your spring crops are done, and they’ll be ready as your summer crops are finishing. They’re not competing with peak-season bed space in most garden configurations.

Growing requirements

Start seeds indoors 10-12 weeks before the last frost date. Leek seeds germinate in 7-14 days at 65-70°F. The seedlings are thin and grass-like - resembling chive seedlings more than onion seedlings. Pot on or transplant to cell trays when seedlings reach 3-4 inches tall, maintaining spacing to prevent damping off.

Transplant to the garden when seedlings are pencil-width or slightly thinner, after all frost risk has passed. The standard method for blanching shanks: dig a 4-6 inch deep trench, set transplants 6 inches apart and 4-6 inches deep in the trench, and backfill loosely. As plants grow, gradually fill the trench - the soil excludes light from the lower shank, creating the white, mild-flavored portion you’re after. Alternatively, use a dibber to make a 6-inch hole, drop the seedling in, water in (don’t backfill), and allow soil to fill naturally over the season.

Soil pH of 6.0-7.0. Leeks are moderate-to-heavy feeders. Work in 2-3 inches of compost before transplanting. A side-dressing of balanced fertilizer when plants are 6-8 inches tall accelerates shank development. Regular consistent watering - 1 to 1.5 inches per week without fluctuation - is critical. Irregular watering causes the shank to split internally, which doesn’t affect flavor but makes cleaning more difficult and reduces storage life.

What goes wrong

Leek rust (Puccinia allii) causes orange-yellow pustules on leaves. It’s common in wet conditions and reduces photosynthesis but rarely kills plants or affects shank quality below the leaf break. Remove severely affected leaves; increase air circulation. No chemical treatment is needed for home gardens.

Onion thrips (Thrips tabaci) cause silver streaking on leaves and reduce plant vigor at high populations. Spinosad sprays are effective. Reflective mulch early in the season confuses adults. This is the most economically significant pest of leeks in commercial production (University of Minnesota Extension, Onion Thrips, 2019).

Botrytis leaf blight (Botrytis squamosa) causes pale oval lesions on leaves in wet, cool conditions. Remove affected leaves and improve air circulation. Most problematic in extended wet springs.

Allium leaf miner (Phytomyza gymnostoma) - the invasive fly established in the US Northeast as of 2015 - lays eggs in leek foliage. Larvae mine through leaves and can enter the shank, causing significant damage in affected regions. Row cover at transplanting prevents adult access.

Harvest and storage

Harvest when shanks reach 1-1.5 inches in diameter. Use a garden fork to loosen the soil before pulling - the roots are extensive and the shank can break if you pull hard. Don’t wait for all plants to reach the same size; harvest progressively from largest to smallest, which extends your harvest window by several weeks.

For overwintering varieties, mulch heavily over the row (4-6 inches of straw) before hard frost to keep the soil workable. You can harvest through mulch in late fall and early winter as long as the ground isn’t frozen solid.

Cut off the dark green tops and root base before bringing indoors. Leeks store in the refrigerator for 2-3 weeks, or in a cool basement or root cellar for 4-6 weeks with roots intact and slightly moist. The green tops can be used in stock.

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Related crops: Garlic, Arugula

Related reading: Beginner Homestead Crops - which vegetables provide fresh produce during the hardest part of the shoulder season