How to Grow Leeks (Allium ampeloprasum var. porrum)

How to Grow Leeks (Allium ampeloprasum var. porrum)

Leeks growing in a garden

By Matt Gibson

Leeks look sort of like a green onion on steroids. They are twice as tall as scallion plants and much fatter, ranging from one to three inches wide, but though they are much larger than scallions, their look is otherwise remarkably similar. It is not a great surprise, therefore, that leeks are in fact related to onions, and they are often used culinarily in a similar fashion, as a seasoning component in a number of recipes. Their flavor is similar to onions, though they are typically much lighter, milder, and sweeter. 

Leeks are a cool-weather crop that enjoys temperatures between 55 and 75 degrees F. Similar to collard greens, leeks develop a better flavor if exposed to a light frost or two. The majority of leek varieties are hardy to zones 7 or 8, but some can endure even cooler weather. A very hardy vegetable, leeks in many regions will cosily sit through frost and snow to be harvested when needed. Though less hardy, early season leeks will be ready for harvesting in the fall, while mid and late season leeks are typically ready for pulling in the winter or spring. 

Grow leeks in an open, sunny location with well-tilled soil that is rich in organic matter. Rust, a common fungal disease, can be an issue for leek plants from the summer and after, so look out for rust resistant varieties if possible and leave plenty of space between each plant to promote good air circulation.  In the garden, the white stem (or stalk) end of the leek is hidden beneath the soil, while the leafy green tops, which are called the flag, protrude from the ground with multiple dark green leafs which fan out in various directions like a head of hair. Leeks are technically a biennial plant, though dieback and damage due to hard freezes mean that most gardeners grow it as an annual. 

Leeks are native to the Middle East and the Mediterranean and have been cultivated throughout human history dating back to the ancient Egyptians. The emperor Nero ate leeks daily to strengthen his voice and the Greek physician Hippocrates is said to have prescribed leeks to people as a remedy for nose bleeds. Leeks made several appearances in the world’s oldest cookbook, “On the Subject of Cooking.” Most popularly used in potato and leek soup, leeks can be used in the kitchen in a variety of ways. Leeks are always on the menu in fine dining restaurants and elegant dishes. They are a staple of the diet in the UK, and are commonly used in asian cuisines as well. 

Varieties of Leeks

Leeks are available in two main types, early season and late season leeks. Early season leeks are the less cold-hardy, faster-growing fall varieties which often have lighter green leaves and are typically not winter-hardy north of Zone 8. Early season leeks are usually planted in the spring and harvested in the late summer or early fall. They are quicker growers, smaller in size and milder in flavor in comparison to late season cultivars Late season leeks are the blue-green hardier winter leeks. They are also planted in the springtime, but they are not harvested until late fall or even winter, as they take much longer to grow. Late season leeks are also cold-hardy and can tolerate gradual temperature changes. Here is a list of some of the best varieties to grow, separated into early season and late season categories:

Early Season Leeks

King Richard – One of the most popular varieties, fast growing, pale-green tender shafts mature in about 75 days. Tolerates light frosts. 

Lincoln – In 50 days, slender bunching leeks can be harvested. Mature leeks can be harvested in 75 days. Delicate and sweet flavor. Will endure light frosts. 

Giant Bulgarian – A long thin leek with light green leaves. Popular in Europe, this autumn variety grows tall and tastes incredible. Expect a longer maturation time than most early season leeks. 

Hannibal – This cultivar produces thick stalks that are pure white, topped with dark green leaves. Matures in 75 days. 

Roxton – This rare, hard to find variety produces uniform stalks and bright green leaves. It does not bulb and matures in 85 days. 

Varna – Maturing in 80 days, this leek cultivar produces long, slender shafts that can be harvested early for better flavor. 

Megaton – If you are looking for an early season leek that is very similar to late season leeks, this is the variety you seek. Maturing in 90 days, Megaton produces thick leeks with blue-green leaves. 

Dawn Giant – Often grown to use in competitions, the Dawn Giant produces gigantic leeks that you have to see to believe. Matures in 98 days. 

Pandora – A very uniform variety, the Pandora matures in 90 days and has blue-green leaves. 

Runner –  A very easy to grow cultivar, runner leek plants stand very erect and mature in 105 days. 

Striker – This disease-resistant cultivar produces long, thick shafts that are easy to clean. Matures in 86 days. 

Late Season Leeks:

American Flag – This variety produces long, narrow shafts that are mild and sweet. A good choice for overwintering in mild climates. Matures in 130 days. 

Giant Musselburgh – This hardy heirloom variety produces large, thick stems with a mild flavor. Great for overwintering in mild climates. Bolt resistant. Matures in 105 days.  

Jaune de Poiteau – A rare, historic variety that is popular in Europe. This variety produces wide, thick, edible white shanks and yellow-green leaves. Matures in 100 to 120 days. 

King Sieg – A cross between King Richard and the winter hardy Siegfried, this cultivar produces six inch long shanks with a nice, three inch wide edible part. It has blue-green leaves and matures in just 84 days. 

Bandit – An extremely cold tolerant cultivar, Bandit leeks produce stalks with minimal bulbing and great flavor. Matures in 100 days. 

Lancelot – A popular hardy variety with rich green leaves. Matures in 95 days. 

Blue Solaise – A hard to find French heirloom named for its dark green leaves that develop a blue tinge during cold spells. Produces hardy, thick, medium-length shanks with a mild flavor. Matures in 110 days.  

Surfer – Disease and pest-resistant, the Surfer cultivar matures in 115 days. It produces clean, white stalks topped with blue-green leaves.

Carentan – This vigorous variety produces high yields and matures in 130 days. It is an old European cultivar and it’s seeds are starting to become quite hard to get. 

Jolant – This cultivar is winter hardy and matures in 120 days. It produces medium sized stalks topped with blue-green leaves. 

Tadorna – Maturing in 110 days, this disease resistant cultivar overwinters in just about any climate. 

Growing Conditions for Leeks

For the most part, a leek can take care of itself just fine. However, if you want to have the most flavorful stalks, here’s the best way to ensure a tasty harvest. Partial shade is ideal, but the leek will also handle full sun just fine. However, to get that pure white stalk that we love to eat, the stalk itself must be shielded from the sun so it blanches.

While the ideal temperature is 60 degrees Fahrenheit, leeks tend to be fine in most weather. Most varieties are tolerant of heat as long as they have plenty of water. Long-growing, cool-season varieties can survive most light frost conditions. You never want the plant to freeze, so it might be better to place a cold frame over them in very cold climates.

This allium likes to have about an inch of water per week once it’s established. When it’s young, it needs a bit more. While the leek doesn’t like a soggy soil, keeping it consistently moist is ideal. You can also mound around the base of the plant with either soil or with mulch. This will help to keep the soil around the roots from drying out too quickly.

Leeks enjoy nitrogen-rich and lightly-packed soil that has lots of organic matter. Before planting, work compost through your soil to a depth of about 12″. If you plan on blanching the stalks naturally by starting them deeper, amend the soil to that 12″ depth beneath the lowest point you plan on planting. This ensures that they should have plenty of food to grow on!

Leeks are heavy feeders, but they don’t need much more than compost-enriched soil. Work compost into the ground before planting. Some blood or bone meal will also encourage them to thrive. If you want to use fertilizer, choose a slow-release balanced granular fertilizer. You can also use a liquid fish emulsion, or just add more compost occasionally.

How to Plant Leeks

Most leeks can be planted anytime after the last frost has passed. If you’re direct-seeding them, you can do so about four weeks before the final frost, and they will come up in the spring. If you are planting from seed, it’s best to start leeks in the late winter using a seedling heat mat and grow light. This gives them the warmth that they need to germinate. It also ensures that they have ample light even in the darker months of the year.

You can direct-sow leeks after the danger of frost has ended. However, direct seeding for the leek plant can be tricky, as they don’t like being planted deep and spring rains can wash the seed away. If you opt to do this, it’s generally best to have some sort of cover protecting your garden until the leeks have sprouted.

Plant in tilled rows or in a raised bed. You can also use them as an edible ornamental, as their fan-shaped structure lends itself well to flower backdrops. Be sure that wherever you plant them, the soil is amended to at least 12″ deep with a good amount of compost for best growth.

You can also grow leeks in containers. If doing this, be sure to space them out a bit. One thing leeks do like is a little bit of room for their roots to spread. While they will still grow well in clusters of 2-3 plants, much more than that and they won’t thrive.

When growing leeks in containers, it’s also important to be sure the soil stays moist. You will also want a wide and deep enough container to allow for mounding soil around the stalks to blanch them. Once you have young seedling leek plants, there are a few options that you can use to plant them. The hole method is our recommendation. 

When you start your leeks, you can germinate multiple plants in a single seedling starter tray. When they’re ready to transplant, take clumps of leeks and gently swish their roots around in a bucket of water. This makes the soil separate from the roots. You can then carefully separate the clumps of leeks into individual plants.

Make a 4-6″ deep hole using a shovel handle or wide stick. Gently set a seedling into it, making sure the tips of the leaves are above the soil level. Sprinkle a tiny dusting of soil around to cover the root. Don’t fill the hole in completely, as nature can handle that. Just be sure the roots themselves are covered. The leek will grow just fine.

If you have lots of plants, you can use the trenching method. Make a long, deep trench. Place a leek in it and push the soil around it, covering the roots. Use just enough soil to keep your plant upright. As the leek grows, push more soil around it to keep the stalk covered. Continue adding soil over time, keeping the stalk covered to promote blanching.

Care for Leeks

If you want to maximize space you can grow fast-growing salad leaves in between your newly planted leeks while you wait for them to establish. Salad crops are shallow-rooted so they won’t compete with the deeply-planted leeks. By midsummer the leeks will need all available space to encourage high light levels and good air circulation.

Easy-care leeks need very little attention. Water the plants in very dry weather and keep the ground between the leeks weed-free by hand weeding or hoeing weekly.

If you want really long, white stems, you can ‘blanch’ your leeks two to three weeks before you want to harvest them. Simply draw the soil up around the shanks to exclude light, or tie cardboard tubes around the stems.

How to Propagate Leeks

You can propagate leeks by seed or by bulbil. Most commonly, seed is used as it’s more reliable and you don’t lose leeks to the bulb-producing process. Follow the process for planting seed as shown above and you’ll have leeks. Propagating by bulbils (sometimes referred to as pips) can be tricky. First, your leek needs to be producing bulbils along the stalk, which can be hard to identify while it’s in the ground. If you harvest a leek and find some, it’s worth trying to replant them!

Carefully separate the bulbils from their mother stalk, and then tuck the base gently into some soil to entice it to set roots. The rooting process can take a little while, but as long as the bulbil’s shoot appears to be green, you have a chance of it forming an exact clone of its parent leek. Once you’ve separated bulbils from the parent, you can replant the parent as well to encourage it to produce more offspring. If a plant is generating a lot of bulbils, it may already be past the edible stage. A plant with only a few bulbils shouldn’t have changed its flavor noticeably.

Garden Pests and Diseases of Leeks

In the United States, the leek is one of the few plants that is almost entirely pest-free. Like other alliums, most pests avoid the pungent onion, garlic, or leek leaves. They’re just too strong for our pests. However, in the UK, the leek moth is a concern. The larvae of the leek moth are tiny caterpillars that tunnel into the leaf stalk to feed, causing brownish patches. Older caterpillars may tunnel directly down the center of the stalk, causing possible rotting or withering issues. After a month or so of feeding, the caterpillar will then pupate on the plant foliage.

While the leek moth is a problem, using a product that controls caterpillars such as Monterey BT will help wipe them out. You can also remove and destroy affected leek plants, which destroys the larvae inside it too. Hand-picking larvae and preventing moths by using floating row covers also works well.

There is one other pest which can attack your leeks: thrips. These small bugs can be controlled by releasing beneficial insects such as ladybugs and lacewings into your garden. However, you should also keep the area near your leeks clear of plant debris and grass. Mulch is fine, but debris or living grass is a home for the thrips!

If your leek patch has a severe infestation of thrips, you can still save them. You can use neem oil to deter the pests. An insecticidal soap will also work in a similar fashion. A good choice would be Safer Brand Insect Killing Soap. Finally, pyrethrin-based sprays will kill thrips if nothing else works. Some good options for pyrethrin sprays include PyGanic and Take Down Garden Spray.

Leeks are mostly disease-free. The only diseases which typically impact them are those typically caused by humidity or moisture on the leaves. Thus, rust or powdery mildew can become problems, as can white tip disease.

Rust is a fungal infection that looks like orangish patches on the leaves. If you discover rust on your leek, don’t panic! Rust is generally just a cosmetic issue. As it tends to impact the leaves more than the stalk, and we prefer to eat the stalk, you can simply remove any rust patches you discover and destroy them.

To prevent rust, rotate your crops regularly so the fungus can’t take hold. You can also use a fungicide such as Safer Brand Garden Fungicide to control rust when it appears.

Powdery mildew isn’t common on leeks, but it can happen, especially if other nearby plants are suffering from it. To treat this, spray neem oil on all leaf surfaces. It should clear up very quickly.

White tip disease, also referred to as white tip of leek, is a fungal infection. It usually results from infected soil splashing up onto the leaves, and can also impact onions. While it’s far more common in the UK than elsewhere, it’s not entirely unknown in the United States. You’ll need a chlorothalonil fungicide such as Bonide Fung-Onil to repair plants suffering from white tip.

harvested leeks

How to Harvest Leeks

You can start pulling leeks from the ground just about anytime. Typically, you’d let them get at least 1 inch or larger in diameter for the big white stems, but you can dig young ones to eat like scallions. If the soil is moist, they may just pull right out of the ground. If they resist, use a spading fork to loosen soil and then gently pull leeks by grabbing them at their base. In zones 7 and warmer, you should be able to harvest leeks all winter long.

In colder areas, extend the harvest season by mulching deeply around plants (up to 1 foot deep) before a hard freeze. You could continue harvesting leeks until they are locked frozen into the ground, but don’t let that happen. Dig them first and store. Wash the stems thoroughly to remove soil and grit that may have collected between the leaves.

How to Store Leeks

For short-term storage (up to one week), tuck stems into an airtight plastic bag and place in the refrigerator crisper. For longer storage in coldest zones, dig leeks with roots attached. Cut leaves back until just an inch of green remains on each leaf. Place stems in a box (root side down) and pack with sawdust, clean sand, or vermiculite. Keep the packing moist and store in a cool place. Stems will keep up to 8 weeks.

For long-term storage, fresh leeks can be frozen either whole or chopped with a little bit of preparation. The first step for freezing leeks for storage is to clean them well, as they can hold a lot of sandy soil which can get trapped in between the plant’s layers. How you plan to use the leeks should determine how much of the green stem you will use. For stocks, most of the leeks can be used. For stir-fries and braising, you should use only the white part of the leek. 

To freeze chopped leeks, first remove the dark green leafy ends and the root. Next, slice the white stalk in half lengthwise and then chop the leek crosswise to create half-moon shaped pieces. Then, place the chopped leeks into a bowl and fill with cold water and move the pieces around swiftly to encourage the sand and soil to sink to the bottom of the bowl.

Let the leeks sit in the water for a few minutes and then, using a slotted spoon, scoop out the pieces. If you are cleaning a lot of leeks, you might use a colander instead, partially submerging the colander in a large bowl of water. Move the leeks around swiftly to clean them just as described before, but drain quickly by pulling up the colander when they are sufficiently cleaned. 

After cleaning, place leeks on a clean dry towel or paper towel and allow them to air dry. Flash freeze them by spreading them out on a sheet tray in a single layer and place them in the freezer until just frozen. Laying out a sheet of waxed paper on the tray before spreading out the leeks could help make the transfer easier once frozen. 

In conclusion, there is one final tip to help you keep your leeks from getting lots of soil trapped inside of them, which makes them so hard to clean. Leeks have a bad reputation for being gritty. Soil can easily become trapped between the leaves, as they grow. To keep them cleaner, you can slip the cardboard tube from paper towels or toilet paper over the young plants. The tube will eventually disintegrate, but it will keep the grit out. Now you are well equipped with everything you need to know to grow the best leeks in your neighborhood. 

Learn More About Leeks

https://www.growveg.com/guides/growing-leeks-from-sowing-to-harvest/

https://www.finegardening.com/article/how-to-grow-leeks

Related

“How to Grow Leeks (Allium ampeloprasum var. porrum)” was first posted here

Leave a Reply

Get Your Garden Right The First TimeLearn exactly how to build and care for your garden. Sign up and never miss awesome gardening tips and ideas.