Leek also known as Allium porrum, is a biennial vegetable in the family Liliaceae, grown for its edible bulb and leaves. The botanical name of leek is Allium ampeloprasum. The edible part of the plant is a bundle of leaf sheaths that is sometimes erroneously called a stem or stalk. The genus Allium also contains the onion, garlic, shallot, scallion, chive, and Chinese onion. Three closely related vegetables, elephant garlic, kurrat and Persian leek or tareh, are also cultivars of A. ampeloprasum, although different in their uses as food. Leeks are toxic to pets.
The plant is a slightly developed bulb attached to a cylindrical stem formed by the overlapping thick, flat leaves. The plant can produce clusters of white, pink or purple flowers and blue-black seeds in the second year. The plant can be grown as an annual, harvested after one growing season or as a biennial with two growing seasons. Although modern leek does not grow wild, it was likely domesticated from wild ancestors in the Mediterranean region. 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.
Table of Contents
1 - 3 feet
6 - 12 inches
6.0 - 7.0
Growth Nutrition of Leek
Leeks require a lot of nitrogen. Give plants a supplemental feeding of liquid fish emulsion or other fertilizer about 3 weeks after planting; continue to fertilize every 3-4 weeks thereafter. If you use a dry granular fertilizer, water it in well.
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.
'Laura': It is a medium length, extremely hardy leek. Upright leaves are dark blue-green. It matures in 180 days.
'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.
'Otina': It is a French variety bred for mild and delicate flavor. Very vigorous and rapid growing, with blue-green leaves. It matures in 120 days.
'Titan': It is an older but reliable variety. It matures in 120 days.
'Durabel': It is a sturdy, thick winter leek with a mild flavor and tender texture. It matures in 125 days.
'Bandit': It is a short, sweet leek that can grow very thick with very little bulbing. Leaf color is blue-green. It is very winter hardy. It matures in 135 days.
'Columbus': It is a medium-sized leek that stays long and tall with very little tendency to bulb. The leaves are a blue-green. It has some winter hardiness but should be mulched. It matures in 80 days.
'Rival': It is a tall summer leek it can grow to 36” with 9” shaft that can have a large, 2” diameter. The leaves are green. It matures in 80 days.
'Jolant': It is a medium-sized leek with a 8-9” shaft and blue/green leaves. Hardy, even bulbs. Winter hardy. It matures in 100 days.
'Lancelot': It is a short leek with a large, cylindrical shaft. The leaf color is a gray-green. Winter hardy. It matures in 105 days.
'Splendid': It is a rapid and vigorous grower, making a good size before fall (important since it is very winter tender). The 7-8 inch medium-green, non-bulbous stalks are easily blanched. It matures in 105 days.
'Albinstar Baby Leek': It is a new Dutch variety developed for the baby leek market. Ready to harvest at ½ inch diameter but can be left in the ground to grow larger. Deep green leaves. It matures in 110 days.
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.
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.
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.
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.
Leek Plant Care
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.
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.
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.
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.
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.
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.
Pruning and Propagating Leeks
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.
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:
Remove a healthy leaf from the plant with its stem and roots still intact.
Cut the leaf down to about an inch above the roots.
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.
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.
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.
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.
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.
Benefits of Leek
1. Fight cancer: Leeks are a good source of allyl sulfides which have been shown to modify certain pathways associated with the growth of tumors.
2. Protects linings of blood vessels: The flavonoid kaempferol which is present in significant amounts in leeks provides protection to the linings of blood vessels, particularly against free radicals or reactive oxygen species. Kaempferol may also increase the production of nitric oxide in the body, a substance that acts as a natural dilator and relaxant of blood vessels, thus allowing blood vessels to rest and lower the risk of hypertension.
3. Protect against heart disease: Studies have shown that members of the allium family have a slight blood pressure lowering effect and may help prevent platelets from clotting which could potentially lead to a heart attack. Leeks can help rid of homocysteine, a molecule that can be very detrimental to cardiovascular health.
4. Weight loss: Leeks are great for weight loss programs as they have a low calorific value. Also, the significant fiber content helps keep one satiated for long and boosts metabolism.
5. Decrease risk of chronic inflammatory diseases: Leeks can fight chronic low-level inflammatory states such as diabetes, obesity and rheumatoid arthritis by virtue of its polyphenol and kaempferol content.
6. Good during pregnancy: Leeks contain a bioactive form of folate called 5-methyltetrahydrofolate. Folate consumption during pregnancy is key to preventing birth defects.
7. Antioxidant properties: The polyphenols found in leeks are known to be strong antioxidants that fight against free radicals that cause chronic disease and aging.
8. Vitamin and mineral action: Leeks contain vitamin C which is important in wound healing and collagen formation. Pyridoxine is important in efficient energy utilization. Vitamin K present in leeks is needed for blood coagulation and for metabolism of bone and connective tissues. Iron is required in the formation of hemoglobin while manganese functions as a coenzyme in many reactions in the body. Eating leeks regularly ensures that you get good amounts of these nutrients.
9. Healthy eyes: Leeks contain lutein and zeaxanthin, two substances that protect the eyes. These substances, known as carotenoids, reduce the risk of cataracts and age-related macular degeneration. These two eye conditions can severely impair vision and negatively impact quality of life. They are common in older people.
Leeks are consumed as a vegetable after cooking and are incorporated into many dishes.
Raw leeks can be used in salads, doing especially well when they are the prime ingredient.