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. 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.
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:
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.
