When to Plant Leeks: Seed-Starting, Transplant and Fall Dates

Leeks are a slow, mild member of the onion family grown for their long white stems rather than a bulb. They take a long season, 120 to 150 days in UMN's guide (some newer varieties about 90) and 70 to 120 days in Maryland's. They are very cold-hardy, so a single spring planting can be harvested from late summer well into winter.

Spring dates by last frost

The table counts back from your average last spring frost. Seeds go in indoors 12 to 10 weeks before the frost, so the transplants are 6 to 10 weeks old at planting out. That fits Utah State's 6 to 8 weeks and UMN's limit of no more than 10 to 15 weeks. Leeks can also be direct seeded in early spring.

Regional examples: University of Minnesota Extension starts seeds indoors in late February or March. Utah State seeds in late March or transplants in early April. In central Maryland, UMD's calendar direct seeds leeks in April, and UMD also suggests a second, later-summer start for a fall crop.

Fall and winter leeks in the South

Where winters are mild, leeks grow through the cool season instead. Clemson says South Carolina gardeners plant leeks in late summer or early fall for harvest in winter or early winter, and that leeks mature best when the average temperature stays below 75°F. It recommends 'Arkansas', and plants take about 120 days from seed. In Florida, UF/IFAS sows leek seeds in fall and harvests in about 3 to 4 months. The Texas A&M planting guides we use don't list leeks, but the same cool-season approach used in neighboring states applies.

Planting leeks deep for long white stems

The pale, tender part of a leek is the part grown out of the light. There are two common ways to get it:

• Dibble holes: Maryland makes holes 5 to 6 inches deep with a 1 to 1¼ inch dowel, drops in a transplant and waters it in without filling the hole; Utah State sets 10 to 12 inch plants into 6 inch holes. The soil washes in over time.
• Trench and hill: UMN plants in a 6 inch furrow and fills it in as the leeks grow, or hills soil up around the stems; Utah State hills 2 to 3 times during the season.

Harvest and winter

Leeks can be pulled at any size. Maryland says small ones can be used like green onions after about 60 days, and both UMN and Clemson consider a leek ready once the stem is about 1 inch across. They take cold well: Maryland says leeks withstand heavy frosts, and UMN says temperatures of 20°F may not harm some varieties. For a harvest into winter, Maryland and UMN cover the row with a heavy straw mulch so you can keep digging; Utah State overwinters them by hilling and mulching. Maryland notes that some varieties are bred for summer and fall harvest and others for overwintering, so check the seed packet.

Where leeks go in the garden

Leeks share the onion family's needs and pests, so rotate them with onions and garlic rather than following them. What to plant with onions covers good and bad neighbors for the whole family, including leeks.

Frequently asked questions

When should I plant leeks?

In cold-winter areas, start seeds indoors 10 to 12 weeks before the last frost and transplant 2 to 4 weeks before it. In the South, plant in late summer or fall for a winter harvest (Clemson, UF/IFAS).

When do you start leek seeds indoors?

UMN starts leek seeds in late February or March in Minnesota. A good rule is 10 to 12 weeks before your last frost, which gives 6- to 10-week-old transplants.

Can you plant leeks in the fall?

In mild-winter areas, yes: Clemson plants leeks in late summer or early fall in South Carolina, and UF/IFAS sows them in fall in Florida. Farther north, leeks are planted in spring and harvested in fall and winter.

How long do leeks take to grow?

About 120 to 150 days in UMN's guide (some newer varieties about 90), or 70 to 120 days in Maryland's. You can pull small leeks earlier and use them like green onions.

Can leeks survive frost?

Yes. Maryland says leeks withstand heavy frosts, and UMN says 20°F may not harm some varieties. A heavy straw mulch lets you keep harvesting into winter.

How deep do you plant leeks?

Many gardeners set transplants into holes 5 to 6 inches deep (Maryland, Utah State) or into a 6-inch trench that is filled in as they grow (UMN), so the stems grow long and white.