Like their cousins onions and garlic, leeks are members of the Allium family, though they are harder to find, giving them a bit of a rare and special reputation. Lucky for us gardeners, learning how to grow leeks is quite simple! Their mild, delicious sweetness and helpful vitamins and antioxidants can be yours directly from your backyard.
What is a Leek?
Leeks (Allium porrum) are essentially a bulbless onion. They are grown for their stout, fountain-shaped stalks that feature a sweet, mild, onion-like flavor. Most varieties have handsome, blue-green leaves.
Leeks are a long-season crop, generally needing 120 to 150 days to mature. Some varieties with shorter days to maturity can be harvested as early as midsummer; others are bred for resistance to freezing temperatures.
How to Grow Leeks from Seed
Leeks are quite easy to start from seeds! Start seeds indoors in your favorite seed starting mix about ten to twelve weeks before you’re ready to plant. In growing zone seven and warmer, leeks can be planted in the fall for a spring harvest and again in late spring for a fall harvest. In other growing zones, leeks should be seeded in very early spring for a fall harvest. Leek seeds germinate best at around 77 degrees Fahrenheit, so keep them in a warm, sunny room. Plant three seeds per cell or pot and thin to the strongest seedling when they are two inches tall.
A Note on Allium Seeds
Allium seeds have a short shelf life of about a year. Be aware of the sell-by date of the seeds you are using, and only buy seeds that are dated for the current season you are in, and plan on using or sharing your leftovers with friends within that season.
How to Grow Leeks from Starts
Leeks can also be purchased as starts, usually shipped to you as bare-rooted bundles in early spring. You can also start your leeks from seed and transplant them following these tips. When working with starts, you’ll want to plant when daytime temperatures have reached at least 45 degrees Fahrenheit.
Choosing a Location
Leeks are a full sun crop but may benefit from partial shade in deep Southern climates. Generally, you’ll want to pick a location that gets six or more hours of sunlight per day to ensure good stalk thickness and maturation. Overly wet locations can also cause problems with rotting stalks so consider adding lots of organic matter to your soils or growing in raised beds if moisture can be a problem in your garden.
Preparing the Bed
In order to prepare your garden bed for leeks, lay a thick layer of compost onto your soil and dig it into the top three inches of soil. This provides plenty of nutrients, helps the soil hold moisture, and creates air pockets so the roots can get oxygen. Before planting, dig a four- to six- inch-deep trench for transplants to be planted in.
Transplanting and Beyond
Plant seedlings in the bottom of the trench six inches apart. Leeks must be planted deep in the soil so that the base of the stem stays out of the sun and becomes blanched. Gradually fill in the trench as the seedlings grow to the point where the soil reaches the cleft where the leaves spread apart. Continue mounding soil around plants until midsummer. We call this soil-mounding process blanching. Blanching causes stalks to grow longer, taste more tender and mild, and turn white. Water regularly and keep the bed free of weeds for vigorous top growth.
Caring for Leeks
Leeks need at least one inch of water cumulatively per week. This means keeping an eye on the precipitation each week or irrigating as it becomes necessary. Newly planted leeks will need a closer watch and should be kept evenly moist until well established. Consider mulching your plants in order to retain moisture throughout the growing season.
Soil and Fertilizer
While leeks don’t need a ton of attention or special care to grow well, they will benefit from a monthly application of a balanced fertilizer like a 5-5-5 or 10-10-10. You may also consider simply topdressing monthly with compost.
Harvesting and Overwintering Leeks
Leeks are generally ready to eat when their stems are about one inch thick. However, if you have a taste for young leeks, they can be harvested at any time. In milder climates (about zone seven and warmer), before your first hard frost in fall, mulch plants with one to six inches of straw to keep the soil from freezing. You can harvest these plants as needed throughout the winter. In areas with colder winters, you’ll want to dig your leeks in late fall and store them.
Leeks can be stored a few different ways. For use in the immediate future, store leeks in an airtight container in the fridge. They’ll stay fresh for about a week.
For a slightly more involved process, leave the roots attached after harvest and trim the top part of the leeks to about an inch long. Place the stems root-end down into a box of sand. The sand should be kept evenly moist, though not waterlogged, and kept in a cool place. These leeks will keep for about eight weeks.
Leeks keep very nicely when frozen too. Slice leeks ahead of time and blanch them in boiling water for one minute. Drain the slices, dry, and keep them in a freezer bag for storage in the freezer. These leeks will keep for about three to four months and are ready to be added to any recipe!
How to Grow Leeks in Pots
When growing leeks in containers you will follow largely the same steps as above. You’ll want to use a container that’s at least 18 inches deep and fill it about halfway with soil to start with. As the leek grows you’ll want to continue adding soil to the stem to create the blanching process as you would in the ground. Remember that leeks need to be 6 inches apart from each other (or any container walls) so take this into account when considering how many leeks to put in one pot.
Tips for Success
Leeks are cold-tolerant, and you can plant as early as late winter with the aid of a floating row cover to protect your seedlings from frost.
Unblanched leeks will have short stalks with tough flesh. If your soil is heavy clay and difficult to trench without risking the leeks sitting in waterlogged soil, you can try slipping cylindrical, ceramic drain tiles or eight to ten inch sections of four inch wide PVC piping around each plant, and mound soil up. These pieces of piping essentially act as individual raised beds for each plant.
Pests to Watch For
Onion maggots can tunnel into leeks, leaving visible holes and making them susceptible to disease. Cut off and destroy any infested areas; portions without tunnels are still edible. This pest thrives in wet soils, so make sure that your beds are made up of well-draining soil.
Types of Leeks
Giant Musselburgh leeks are an heirloom variety that is extremely cold hardy. They grow to be nine to fifteen inches long and two to three inches in diameter - hence “giant” in the name. 120 days to harvest.
American Flag leeks are known for their superior quality and flavor. They produce stalks that are about ten inches long and are a favorite variety of home and market growers. 135 days to harvest.
Lancelot leeks are offered as starts by Sow True Seed. They are a dependable variety that produces 12- to 14-inch-long stalks and shows good bolt resistance when overwintering. 75 days to harvest.
Using Leeks in the Kitchen
Leeks have two distinct parts, a top with darker greenish-blue leaves, and a lower part with white to pale green stalk. The top greens are great to save for veggie stock, but are usually too tough to eat, so we concentrate on eating the tender stalk, which stays pale by blanching. Leeks are delicious when used in soups, stir fries, or omelets. The tender stalk offers a light onion flavor that doesn’t overwhelm the other flavors in the dish.