Leek

About Leek

Leeks are mild members of the onion family grown for their thick white shafts rather than bulbs. They are slow but easy, and many varieties stand well into fall frosts.

Grown as an annual in every zone; some varieties survive temperatures near 20F, so they can be harvested late into fall.

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

• Start seeds indoors: 12 to 14 weeks before the last frost
• Set out plants: 4 weeks before the last frost

Days count from seeding; most varieties need 120 days or more, and a few newer ones mature in about 90. Start seed indoors 8 to 10 weeks before transplanting, and set plants into a 6-inch-deep furrow that you fill in as they grow.

Soil

Well-drained soil high in organic matter; water the soil rather than the leaves to limit disease.

Use well-drained soil high in organic matter with pH 6.0 to 7.0; follow a soil test for phosphorus and potassium (without one, about 2.5 lb of 5-10-10 per 100 sq ft before planting).

Feeding

• midsummer: balanced fertilizer such as 10-10-10. Use about 1 cup per 10 ft of row, 6 inches from the plants, scratch it in and water.

Do not use fresh manure; skip extra phosphorus unless a soil test calls for it.

Harvest

Dig leeks once the stem is more than an inch wide, with a firm white shaft at least 3 inches long. Hilling soil or compost around the stems a few times during the season makes a longer white shaft.

Each leek is dug once, when the stem is over an inch thick with at least 3 inches of white shaft. Leeks handle several frosts, so with mulch you can keep digging them into late fall.

Varieties (11)

Few extension sources describe leek varieties in detail; most give names only. Most leeks need about 120 to 150 days, though some newer types are faster (Minnesota Extension).

Pests to watch for

Onion maggot, Thrips, Slugs, Allium leafminer

Diseases and problems

Rust, Purple blotch, Neck rot

In the kitchen

Cooked in soups (like potato-leek), braised, sauteed or roasted; rinse well, since soil hides between the layers.

Keeping it: Refrigerate leeks unwashed and use them within 7 to 10 days for best flavor; they keep longer but slowly lose quality. Many varieties can also stay in the garden into fall frosts.

Safety: Handling leeks can irritate the skin of some people, and eating very large amounts can upset the stomach (NC State).

Pets: Toxic to dogs, cats and horses (ASPCA): contains N-propyl disulfide, which damages red blood cells and can cause vomiting, anemia, weakness, a fast heart rate and panting.