Leeks are relatives of onions, with a milder, more herbal flavor that sweetens as they cook. Native to Europe and Africa and best planted in the cool early spring or fall months, leeks are characterized by tough, flat, bluish-green leaves encircle each other, forming a cylindrical base at one end and a fan of folded leaves at the other. The leaves grow opposite each other, and the plant takes on an almost flat appearance until the leaves become long and floppy.
Although often considered a root vegetable, leeks do not usually form a bulb. Instead, the edible part is the bottom six inches or so of the cylindrical stalk that is white instead of vibrant green. After a fairly long growing period (around three months), leeks can be harvested and used as an aromatic vegetable in soups and casseroles.
|Botanical Name||Allium ampeloprasum|
|Plant Type||Herbaceous perennial|
|Mature Size||1–3 ft. tall, 6–12 in. wide|
|Sun Exposure||Full sun|
|Soil Type||Sandy, well-drained|
|Soil pH||Neutral to acidic|
|Hardiness Zones||5–10 (USDA)|
|Native Area||Europe, Africa|
Closely related to the onion in both taste and appearance, leeks are an easy-to-grow vegetable great for home chefs. They do best in full sun and a slightly acidic soil pH, although they will tolerate more alkaline soils as well. Since you're growing leeks for their leaves, you'll want to house them in rich soil, with lots of organic matter.
Leeks are shallow-rooted, so use caution when cultivating near the plants and keep the area weed-free. Provide the plants with regular watering—mulching will also help keep the soil cool, retain water, and prevent weeds. Leeks are not heavy feeders, but because they take a while to mature, a mid-season side dressing of composted manure or a high nitrogen fertilizer is beneficial. Leeks are very frost tolerant and, in mild climates, can be left in the garden throughout the winter.
Most varieties of leeks require a fairly long growing season of 120–150 days, although some modern cultivars have been bred for shorter seasons lasting about 90 days. Unlike the cousin the onion, leeks don't die back and signal they are ready to harvest. Instead, they are ready once the base has at least a three-inch white section, and feels firm and solid. Remove from the soil by twisting and pulling or digging.
Leeks prefer a lot of sunshine and should be planted in the sunniest spot you can find in your garden. Ideally, you'll want to ensure they get about eight hours of bright sunlight daily throughout the entirety of their growing season.
Leeks grow best in a sandy, well-drained soil mixture that boasts a pH level between 6.0 and 7.0. A nutritious soil is key to a good leek harvest, so consider amending yours with organic matter or rich compost. When planting leeks, space your seeds at least six inches apart.
To encourage a succulent white stem (the edible part of the plant most frequently used in cooking), leeks must be blanched—another way of saying they should be hidden from the sun so that part of the plant doesn't make chlorophyll and turn green. To do so, plant seeds about six to eight inches deep in the soil, and continue to mound the soil up around the leek as it continues to grow out of the ground, starting around when the stems are an inch thick.
Leeks have shallow root systems and need to be watered frequently in order to thrive. In most environments, a weekly deep watering will suffice—however, if you live in a warmer climate or have been experiencing especially hot weather, you may need to increase your cadence.
Temperature and Humidity
Temperature is not of particular importance when growing leeks. You'll want to plant them in the cool early spring months, but other than that, you really don't need to worry (though they do thrive best in cooler weather). Additionally, leeks are especially cold hardy, able to withstand temperatures well below freezing. Depending on the hardiness zone you live in, you may even be able to grow leeks (as well as other cold-hardy vegetables) throughout winter.
A nutrient-dense soil is very important to the success of your leek harvest. Nitrogen is particularly important to their growth, so look to side-dress their growing area with a balanced fertilizer about halfway through their growing season.
- American Flag: One of the tallest heirloom varietals, the American flag leek has long, narrow shafts and a mild, sweet flavor. They're a good choice to overwinter in mild climates.
- Early Giant: As alluded to by its name, the early giant leek 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 Leek: This tall heirloom variety can reach heights over more than 30 inches, and is typically ready to harvest in 130 days.
How to Grow Leeks From Seed
You can start leeks from either seeds or transplants. In colder climates, seeds can be started indoors, anywhere from eight to 12 weeks before your last spring frost. Move outdoors when temperatures begin to stay above 40 degrees Fahrenheit, and harden them off slowly (for about seven days) before transplanting in the garden.
In warmer climates, where spring and fall are your prime growing seasons, you can either start your seed indoors approximately three to four weeks before your last spring frost and transplant outdoors for an early summer harvest or direct seed in late summer and harvest in winter through early spring.
Common Pests and Diseases
Slugs can be a big issue for leeks (they munch on the leaves), as well as other pests that also bother onions, such as onion maggots, leafminers, and thrips. You can use an organic solvent, like neem oil, to get rid of most pests. However, if a true infestation occurs, your best bet is to rip up the affected crop before the pests have to chance to spread to nearby plants.
Keep an eye out for several common diseases as well, like blight and leek rust, which forms orange pustules on the leaves. Most of these diseases occur in damp weather—to remedy, remove the affected leaves and improve air circulation. New growth should come in healthy.
Damp weather or wet soil can also lead to leaf rot, which shows up as white spots on the tips before they eventually wither and die. There is no cure, but providing good air circulation, allowing the soil to dry between waterings, and removing any plants that appear to be infected will decrease the likelihood of occurrence.