How to Grow and Care for Leeks

growing leeks

The Spruce / Randi Rhoades

Leeks are a relative to onions, garlic, shallots, and chives. They produce bundles of long, narrow, and fairly flat blue-green leaves with a cylindrical white shaft at the base (but not a bulb like onions). They look similar to green onions but with a larger profile. 

Leeks have a slow to moderate growth rate and should be planted in the early spring. They also can be planted in the fall in some areas. Be careful about where you plant them though, as they do have chemical compounds that are toxic to pets.

Common Name Leek
Botanical Name Allium ampeloprasum
Family Amaryllidaceae
Plant Type Vegetable, perennial, annual
Size  1–3 ft. tall, 6–12 in. wide
Sun Exposure  Full sun
Soil Type  Loamy, well-drained
Soil pH  Neutral, acidic
Bloom Time  Spring
Hardiness Zones  5–9 (USDA)
Native Area  Europe, Africa
Toxicity Toxic to pets

How to Plant Leeks

When to Plant

Leeks can be planted right around your area’s last spring frost date. Young plants can survive a light frost, and mature plants can withstand heavy frosts. To get a jump on the growing season, you can start seeds indoors approximately 10 to 12 weeks prior to your projected last spring frost date.

In climates with mild winters (generally zone 7 and above), you also can plant in the fall.

Selecting a Planting Site

Pick a sunny spot that has rich, well-drained soil for your leeks. Raised garden beds and containers also are an option if you don’t have sufficient garden space.

Leeks are shallow-rooted, so use caution when cultivating other plants near them. And keep the area weed-free to avoid competition. For gardeners with limited space, you can plant shallow-rooted, fast-growing salad greens in between your leeks while waiting for them to establish.

Spacing, Depth, and Support

Plant seeds roughly 1/4 inch deep and 6 to 8 inches apart. When planting seedlings, mound soil around the stem up to the first green leaf. Rows should be at least a foot apart. A support structure shouldn't be necessary.

Leek Plant Care

Light

Leeks prefer a lot of sunshine. At least six hours of direct sun on most days is ideal for them. Too little sun can result in weak and floppy growth.

Soil

A well-drained loamy or sandy soil with a slightly acidic to neutral soil pH is best for leeks. A nutritious soil also is key for healthy growth, so consider amending your soil with organic matter or rich compost.

Water

Leeks have shallow root systems and need to be watered frequently—roughly an inch per week—to thrive. In most environments, a weekly deep watering will suffice. However, if you live in a warm climate or have been experiencing especially hot weather, you might need to increase your watering. Mulching will also help to keep the soil cool, retain moisture, and prevent weeds.

Temperature and Humidity

Temperature is not of particular importance when growing leeks. It's best to plant them once the temperature is above 45 degrees Fahrenheit in the spring, though they do have fairly good cold tolerance. And they do best when temperatures are between 55 and 75 degrees Fahrenheit. Likewise, humidity generally isn't a factor as long as you maintain sufficient soil moisture and have good air flow around the plants.

Fertilizer

Leeks are not heavy feeders. But because they take a while to mature, nutrient-dense soil is important to support them for the duration of their growth. A midsummer side dressing of composted manure or an organic high-nitrogen fertilizer can be beneficial. For the amount to use, follow the product label instructions.

Pollination

Because most people harvest their leeks before they flower and go to seed, pollination won’t be an issue. If you do let your leeks flower, bees and other insects will assist in pollination.

leek seeds
The Spruce / Randi Rhoades
leek ready for harvest
The Spruce / Randi Rhoades
leek harvest
The Spruce / Randi Rhoades

Types of Leeks

  • 'American Flag': One of the tallest heirloom varietals, American Flag has long, narrow shafts and a mild, sweet flavor. It's a good choice to overwinter in mild climates.
  • 'Early Giant': As alluded to by its name, Early Giant has one of the shorter maturation periods, ready to harvest in around 98 days. It also boasts especially thick stems with a mild flavor.
  • 'Autumn Giant': This tall heirloom variety can reach heights over more than 30 inches and is typically ready to harvest in 130 days.
  • 'Varna': Perfect for early-season planting, Varna matures in 50 days and is a tall “bunching” type developed for thick direct seeding to produce clumps of slender plants.
  • 'King Richard': This variety matures in just 75 days with long, slender stems that stay sweet and tender. It can be sown densely to grow mini leeks for use as a garnish or in soups and salads.

Leeks vs. Onions

Leeks are a relative of onions and share many similar characteristics. However, leeks don't grow bulbs like onions do. And while they have an onion-like flavor, it's more mild and herbal, sweetening as it's cooked.

Harvesting Leeks

Unlike their cousin, the onion, leeks don't die back and signal they are ready to harvest. Instead, they are ready once the stem width is larger than roughly an inch and feels firm.

To harvest, remove the leeks from the soil by twisting and pulling or digging. In warm climates, your plants should keep growing and producing harvestable leeks throughout the winter. And in cold climates, you can prolong your harvest by adding a thick layer of mulch around your plants.

Wash the leaves to remove any soil. They can be stored in the refrigerator for about a week. They also can be blanched and frozen for up to a year.

How to Grow Leeks in Pots

Growing leeks in a container is a good option if you don’t have sufficient garden space. It also allows you to closely control light and moisture conditions. Choose a container that’s about a foot wide and 18 inches deep. You can add more than one plant to a container as long as each has roughly 6 inches of space on all sides. Crowded plants will result in smaller leaves. 

Make sure the container has ample drainage holes. An unglazed clay pot is ideal because it will allow excess soil moisture to evaporate through its walls as well.

Pruning

Leeks generally don't require pruning throughout the growing season besides harvesting mature leaves. However, it's important to remove any dead or diseased leaves as soon as possible to prevent them from weakening the whole plant.

Propagating Leeks

Leeks can easily be regrown from scraps to create new plants. This is a great way to put stems to use that you’re not going to eat. You can do this at any point during the growing season. Here’s how:

  1. Remove a healthy leaf from the plant with its stem and roots still intact.
  2. Cut the leaf down to about an inch above the roots. 
  3. Place the piece roots down in a small glass of water, and put the glass by a bright window. Make sure the stem portion isn’t submerged in the water. 
  4. Refresh the water every couple of days. You should see new growth within about a week. You can either harvest this new growth as needed or plant the leeks in soil for more substantial growth.

How to Grow Leeks From Seed

To start seeds indoors, fill a shallow tray with moist soilless potting mix. Just lightly cover the seeds with the potting mix, as they need some light to germinate. For best results, use a heat mat to keep the soil temperature at around 70 degrees Fahrenheit. Place the container by a bright window or under grow lights, and maintain moist but not soggy soil. You should see germination in about two weeks.

Potting and Repotting Leeks

Use a quality organic vegetable potting mix for potting leaks. Mixing some compost into the potting mix can help to give your plants a boost. Repotting generally won't be necessary. It's best to select a container that will accommodate the leeks' mature size, so you don't have to disturb their roots.

Overwintering

Gardeners in cold climates often harvest what they can from their leeks before freezing temperatures set in and then start with new plants the next growing season. However, in warm climates you can leave leeks in the ground over winter. Growing them in raised beds can help to maintain a suitable soil temperature.

Common Pests and Plant Diseases

The pests and diseases that affect onions also can impact leeks. Some common pests include onion thrips and maggots. Minor infestations can be treated with neem oil. Moreover, common diseases include white rot, downy mildew, and purple blotch. Many fungal diseases occur during damp weather, so always make sure your leeks are in well-draining soil and have good air circulation.

FAQ
  • Are leeks easy to grow?

    Leeks are fairly easy to grow as long as you can provide them with sufficient water, nutrients, and sunlight. It's also important to keep weeds away from them to reduce competition.

  • How long does it take to grow leeks?

    Most varieties of leeks require a fairly long growing season of around 120 to 150 days on average. However, some modern cultivars have been bred for shorter seasons lasting around 90 days on average.

  • Do leeks come back every year?

    Leeks technically are perennials, though many gardeners treat them as annuals. They can overwinter in the ground in warm climates.

Article Sources
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  1. Leeks. ASPCA.