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
Leeks are a hardy vegetable that can, for the most part, take care of themselves. But, for gardeners who want to produce the most flavorful stalks, a little bit of TLC can help to ensure a delicious harvest. Leeks can handle full sun without a fuss, but locations that get partial shade are preferred. The key to getting the pure white stalk that many gardeners covet, however, is to place your leek plants in a location where the stalk itself is shielded from the sun so that it naturally blanches.
Leeks will do fine in most weather, but the ideal temperature is 60 degrees F. As long as you provide your leeks with plenty of water, they will be tolerant of heat, even for extended periods. Late season leek varieties that take longer to mature can survive most mild frost conditions. Leeks should never freeze, however, so you may want to place a cold frame over your plants if you are in an extremely cold area.
Once your leeks are established, provide about an inch of water per week. Leeks need a bit more water when they’re young, but they don’t like soggy soil at all. The goal is to keep the soil consistently moist. Using soil or mulch, you can mound a bit of extra material around the base of the plant to help keep the soul around the roots from getting dry too quickly.
Leeks prefer soil that is amended with lots of organic matter and is nitrogen rich as well as lightly-packed. Work compost into your soil to 12 inches deep before planting. If you intend to blanch your stalks, you will want to amend the soil even deeper, around 12 inches below the lowest you plan on planting your leeks to ensure that they have plenty of nutrients to grow on.
Leeks are considered heavy feeders, but surprisingly, they don’t need a whole lot more than a well worked compost-rich soil to thrive, so be sure to work in lots of compost before planting. If you want to give your leeks a little bit more encouragement, some blood or bone meal will help them thrive. If you want to use fertilizer as well, a slow-release balanced granular fertilizer is suggested. You can also just top dress with compost occasionally throughout the growing season, or use a liquid fish emulsion.
How to Plant Leeks
Anytime after the last frost has passed, leeks can be safely planted. If you are direct-seeding your leek plants, they will come up in the spring if you sow them about four weeks prior to the final frost. It is best to start your leeks in the late winter indoors using a heat mat under your seedling tray and a grow light if you are planting from seed. Using a heat mat will give the seeds the warmth they require to germinate. Using a grow light helps to make sure that your leeks get plenty of light even in the darker months.
After the danger of frost has passed, leeks can be direct-sown. Unfortunately, direct seeding leek seeds can be a little bit tough. Spring rains can wash the seed away if it is planted too shallow, and leek seeds won’t sprout if they are planted too deep. If you decide to direct-sow your leeks, use some kind of protective cover to help keep your seeds from washing away until the seedlings come up.
Plant your leeks in a raised bed or in tilled rows. The fan-shaped tops of leek plants make excellent flower backdrops as well, so you can use them in the garden as an ornamental until they are ready to harvest. Wherever you decide to plant them, amend the soil to at least 12 inches deep and use a good amount of compost for the best results during the growing season.
Leeks also perform well when grown in containers, as long as they are spaced out a bit more than usual. Leeks enjoy a bit of extra room for their roots to grow into and spread out in. Clusters of two to three plants will still grow well, but larger clusters will not thrive, as their roots will not be able to spread out comfortably. You will want to keep the soil in your containers moist at all times and you will need a container that is wide and deep enough to give you plenty of room for mounding soil or mulch around the stalks of each plant to blanch them.
Once you have your seedlings sprouted, there are two options for planting, the hole method, and the trenching method. We recommend the hole method. When you start your leeks, try to germinate multiple plants in a single seedling starter tray. Once they are ready to transplant, take them out in clumps with the soil still attached to the roots and carefully swish their roots around in some water so that the soil will separate from them easily.
Once the roots are exposed, gently separate the clumps of leeks into single plants. Make a hole about four to six inches deep using a wide stick or a shovel handle. Set a seedling into the hole carefully, making sure the tips of the leaves stay above soil level. Cover the root by sprinkling a small amount of soil over it. Allow the hole to fill in naturally on its own, only covering the roots with soil without filling the hole up completely.
Use the trenching method only if you have lots of leek plants to sow. Make a long, deep trench in your garden soil. Place each leek into the trench one at a time and push the soil around it to cover the roots. Use only enough soil to keep your plant standing up straight. As the leek grows taller, push more soil around it in order to keep the stalk from being exposed. Continue to add soil overtime to keep the stalk covered so that it will blanch naturally.
Care for Leeks
There’s not a lot to do when it comes to care for leek plants once they are established. Water the plants when the weather is dry and pull up any weeds you see by hand or with a garden hoe. Keep the ground weed free by performing this task weekly, as your leeks will not be happy to share their moisture and nutrients with any squatters.
If you want to end up with long, white stems come harvest time, you can blanch your leeks for two to three weeks. To do this, just pack some surrounding soil up around the shanks to keep them from being exposed to direct sun or tie cardboard tubes (like toilet paper rolls) around the stems to shade them from the sunlight.
How to Propagate Leeks
Leeks can be propagated by bulbil or by seed, though propagation by seed is the most common and most reliable method which assures that you don’t lose leeks to the bulb-producing process. To propagate by seed, just follow the planting method outlined in the section above. Propagating by bulbils can be somewhat tricky. Your leek needs to be producing bulbs on the stalk, which can be tough to tell when the stalk is buried underground. If you harvest a leek and find some growing on the stalk, it can be well worth attempting to replant it to give it a try.
Carefully separate the bulbils from their stalk and entice it to set roots by gently tucking the base into some soil. You have a chance of it forming an exact replica of the parent leek as long as the bulbil’s shoot looks green, but the rooting process may take a little while. You can replant the parent as well, once you’ve separated the bulbils from it, to encourage it to grow more bulbils. If a plant is making lots of bulbils, it is likely already past being edible anyway. A leek plant with only a few bulbils shouldn’t have a noticeably compromised flavor.
Garden Pests and Diseases of Leeks
Luckily for gardeners in the US, leeks are one of the handful of plants that are nearly pest-free. Most pests avoid the pungent taste and odor of alliums like onion, garlic, or leeks. They’re simply too strong for pests to partake in. The leek moth, however, can be an issue for UK gardeners. The moth’s larvae are tiny caterpillars that tunnel into the center of the stalk, causing rotting and withering. After a month of feasting on your leek plants, the caterpillar will begin to pupate on the plant’s leaves.
To wipe out leek moths, use products that are intended for caterpillar control, such as Monterey BT. Other control methods include hand picking larvae and using floating row covers to prevent moths from laying their eggs. You may also choose to just remove and destroy affected plants, which will destroy the larvae as well.
Thrips is one other pest that occasionally attacks leek plants. Thrips are controlled by releasing beneficial insects like lacewings and ladybugs into your garden. Living grass is a home for thrips, so do your best to keep grasses out of your garden beds.
Other prevention techniques that are usually successful include keeping the garden area clear of grass and plant debris, and mulching to prevent grass and weeds from growing in the garden around your leek plants. Serious thrips infestations call for neem oil or insecticidal soap treatments. If nothing else works, pyrethrin-based sprays will kill them off, though it’s a tough call, as you may not want to spray chemicals on plants that you plan to consume.
Leeks are also practically disease-free. The only diseases that typically impact them are powdery mildew and white tip disease, both of which are caused by humidity or moisture on the plant’s foliage. Powdery mildew isn’t a common disease for leek plants, but if nearby plants have it, there is a chance that it could spread to your leeks too. To treat this, spray neem oil on all leaf surfaces to quickly solve the issue.
White tip disease is a fungal infection that is caused by infected soil particles splashing onto the plant’s foliage. Onions are also prone to white tip issues. Though it is most common in the UK, white tip occasionally occurs in US gardens. To treat plants suffering from white tip, spray them with a chlorothalonil fungicide.
Occasionally, leep plants may be impacted by rust, a fungal infection that appears in orange patches on the plant’s leaves. Rust is usually nothing more than a cosmetic issue, as it generally only affects the leaves of the plant, leaving the stalk untouched. If you notice any rust patches, just remove them from the plant and destroy them. To prevent rust, practice crop rotation and use a fungicide for control.
How to Harvest Leeks
Leeks can be harvested at will anytime in the growing cycle. Usually, gardeners wait until they are at least one inch or larger in diameter in order to enjoy their big white stems, but you can also dig them up when they are young to eat like scallions. If the soil around them is moist, they can often be pulled right from the ground easily. If there is resistance, use a spading fork to loosen the soil and then gently pull them up by supporting them at their base. You can harvest leeks all throughout the winter in zones seven and warmer.
In colder climates, the harvest season can by putting down a very thick layer of mulch around your leek plants, up to one foot deep, before a suspected hard freeze. Don’t allow the leeks to become locked into the ground by freezing. Harvest them first and store them. After harvesting, wash the stems well to remove any soil and dirt that might have collected between the plant’s leaves.
How to Store Leeks
To keep your leeks fresh for about a week, place the stems in an airtight plastic bag and store them in your refrigerator’s crisper drawer. In the coldest climates, longer storage is possible by digging the leeks with roots attached. Just cut back leaves until just an inch is left on each leaf and place the stems in a box with the root side down. Then pack the box with sawdust, vermiculite, or clean sand. Keep the packing moist and store in a cool place. Stems stored like this will keep up to eight 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.
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.