Ultimate Guide to Growing Leeks

If you are looking for a hardy, low maintenance vegetable to add to your winter garden, why not try growing leeks? These pleasingly trouble free vegetables produce attractive, nutritious stems from fall until spring. Providing you with a reliable crop of versatile, fresh vegetables when other harvests are thin on the ground.

Gardeners in nearly every USDA Zone can enjoy some success growing leeks. These are cool weather vegetables that happily tolerate frost and snow. In USDA Zones 7 and warmer they can be overwintered for a late winter or early spring harvest.

Resembling giant scallions, with attractive leafy stems, the long white bulb at the base of the leek is the edible section. A member of the onion family, but a lot easier to grow than onions, leeks are ideal for raised beds and containers. Packed with flavors, they are a tasty addition to a range of stews and vegetable dishes. In fact the home grown leek often has more flavor than the shop brought specimen.

1 Leeks extend your growing season
While they may take up a lot of space, planting leeks is a great way to extend your growing season throughout the fall and winter. 

If you want to add leeks to your winter garden, this guide will take you through everything that you need to know.

Different Varieties to Try

Before you begin growing you will need to select a suitable variety of leek.

They are usually divided into 3 different categories:

  • Early Season,
  • Mid Season,
  • Late Season

Early Season varieties have a mild flavor. Requiring 50 to 100 days of growth before they are ready for harvest, early season varieties typically mature from late summer until early fall. Frost sensitive, they won’t survive exposure to frost or cold temperatures. Some varieties, such as King Richard can be lifted as early as July in certain growing conditions. King Richard stems can be grown in close proximity to each other for small baby or mini leeks. Carlton is another reliable, quick growing early variety. It is primarily grown for its tall, straight stems and excellent flavor.

Mid Season cultivars are usually harvested from December to February. Edison is a disease resistant mid season variety that can also be harvested early for baby leeks. Oarsman is a reliable variety with a vigorous growth habit. It is also pleasingly rust and bolting resistant. One of the most well known mid season varieties is Musselburgh. This reliable cultivar has a good flavor and texture which it retains after cooking. It is hardy enough to tolerate cold winters.

Late Season varieties have a long growing season. Depending on the variety it can take 120 to 180 days from sowing the seeds before they are ready to harvest. Usually lifted in late February, late season varieties are known for their strong flavor and wide stalks. Most varieties require blanching. Blauwgroene Winter Bandit is one of the most reliable examples of a late season leek. Winter hardy it is also rust and bolt tolerant. Below Zero F1 Hybrid is another vigorous cultivar that is cold tolerant.

2 Leeks grow at different rates
Different varieties grow and mature at different rates, enabling you to extend your growing season significantly. It also means gardeners in nearly every climate will find at least one appropriate variety. 

In warmer climates, where winters are short, try growing early or mid season varieties. In cooler climates you can also try planting late season leeks. To prolong the harvest sow a selection of seeds from each category. This enables you to enjoy a continuous supply of fresh vegetables throughout the winter.

Seeds can be purchased from garden stores and plant nurseries.

Don’t worry about using all your seeds in the first year. If properly stored, in an airtight tin, they keep for up to 4 years.

Where to Grow

You can enjoy growing leeks in most soil conditions, just avoid anywhere overly waterlogged. These plants do best in evenly moist, light soils that have been heavily manured or enriched. Before planting work a decent amount of well-rotted garden compost evenly, throughout the soil to create the ideal growing conditions.

Allow the soil time to settle after working in any amendments before you begin sowing or planting. Leeks struggle to grow in overly rich soil and can become tough or coarse. They may also produce too much foliage.

Avoid growing your vegetables in the same soil every year. This increases the risk of pests and diseases targeting your crops. Employing even a basic crop rotation system, as outlined here, benefits your entire vegetable garden. In this system, leeks should follow cabbages and peas. Don’t plant them in the soil straight after lifting potatoes. The soil will be too loose. Leeks require a firm soil to fully form.

Your chosen position should also be light and sunny with some protection from strong winds.

3 Leeks take up space
Growing leeks like firm soil, light and space. If you can provide these three elements you should be rewarded with a healthy crop of nutritious, tasty stems. 

You can also grow these vegetables in pots and raised beds. Fill your chosen container with a fine, well draining soil. If you are planting in pots, they should be deep enough to comfortably hold the plant’s entire root system. Plant in pots at least 18 to 20 inches deep.

When to Plant

Leeks enjoy a long growing season. Depending on the variety you are growing you can start your seeds undercover in a greenhouse from early February.

Early season varieties, also known as Summer varieties, can be started in seed trays undercover or in propagators from mid February onwards. They can be transplanted into the garden from mid April onwards.

Mid Season, or Fall varieties, can be started undercover in the middle of March for transplanting in mid May.

Late season or Winter varieties can be started undercover in early May and planted out in June.

While transplanting can be tricky it is preferable when growing vegetables such as leeks that have a long growing season and take up a lot of space. Starting undercover before transplanting out later in the summer allows you to make the most of your growing space.

Sowing the Seeds

Seeds are best started undercover in pots or modular trays. The AQUEENLY Seed Starter Tray is a modular tray with a fitted lid. This enables you to better control the temperature and humidity levels around your growing seedlings.

Fill the modular trays with fresh seed compost. This has a finer texture and fewer nutrients than standard multi-purpose composts. As you fill the tray, rub the soil through your hands to break up any clumps.

Make a small depression in the soil. If you are sowing in modular trays, sow 2 seeds per module. Sow seeds thinly about 1 inch apart and a quarter of an inch deep. Cover with a light layer of seed compost before gently firming down the soil and watering well.

Place in a light, warm position and regularly check the soil. It should remain evenly moist.

Germination takes 14 to 21 days. Thin out the seedlings as soon after germination as possible, within 6 weeks of sowing if possible, to 2 inches apart. A few weeks later when the seeds are growing well, thin out again to a spacing of about 4 inches. If you have started the seeds in modular trays, pick out the weakest seedling in each module allowing only the strongest to grow on.

Allow the seedlings to grow on in their warm, light position. Continue to keep the soil moist.

Transplanting Seedlings

Begin hardening off the seedlings when they are about as thick as a pencil and around 8 inches tall. Once they are fully acclimatized they can be transplanted into their final position.

Transplanting during a showery period helps the plants to settle more quickly. Otherwise moisten the soil yourself with a garden hose.

To transplant, make a hole in the soil roughly 6 inches deep. If you are using a dibber to make the hole, wiggle it slightly so that the top of the hole is larger than the bottom. Ideally the top of the hole should be about 2 inches in diameter.

Carefully remove the seedling from the tray and gently tease the roots apart. When placed in the hole the roots should sit neatly at the bottom of the hole. The roots should be about 1 inch long. If they are too long trim them back a little with a small, clean pair of garden scissors.  You can also slightly trim the leaves if they are too long or touching the ground.

Place the leek in the center of the hole and fill with water. Allow the water to drain away. The soil will naturally fall down into the hole. There is no need to backfill the hole yourself.

Space the seedlings out so that they are 6 to 9 inches apart. The more space you give the seedlings the larger they will become.

Transplanting into Trenches

You can also try growing leeks in trenches. This is a great option if you have deep, fertile soil.

Dig a trench about 1 ft deep. Place a 3 inch thick layer of well-rotted compost in the bottom of the trench. Cover with a 6 inch layer of topsoil. Plant the seedlings on the topsoil, they should sit upright. Space the seedlings roughly 10 inches apart. Water well. Like the previous planting method there is no need to backfill the trench.

If you are digging more than one trench, space them roughly 2.5 ft apart.

Transplanting into Pots

Pots should be at least 18 inches deep. They should also be clean and have ample drainage holes.

Fill the pot about two thirds full with fresh potting soil and plant the seedlings as described above. Water well. Again there is no need to fill the pot with soil after planting. This can be done, slowly as the plants grow, blanching the stems in the process,

Post Planting Protection

After transplanting, cover the seedlings with a fleece, such as the Agribon Floating Row Crop Cover, to protect the plants from attack by the harmful leek moth. This pest causes low yields and foliage dieback. Make sure that the protective cover is securely pinned down.

Caring for Growing Leeks

Once transplanted, care for growing plants is minimal. Hoe between the rows to keep weeks away. Carefully working and weeding the soil also helps to aerate it. This helps the plants to thrive and also improves soil moisture retention.

4 Keep the soil clear
Keep the ground between the stems clear and tidy. 

If the foliage gets too long, and starts to touch the ground, it can be cut back slightly. Dark foliage can be cut back by about 2 inches in early summer and again in mid summer. You may need to do this for a third time in early fall.

When to Water

Keep the soil well watered until the seedlings are established and new growth is visible. After this, you only need to water your growing leeks in dry weather. Apply about 1 inch of water a week.

How to Fertilize

Apply a liquid fertilizer or liquid manure soon after planting.

Growing leeks are heavy feeders. Poultry manure sprinkled widely around roots is great, as is a liquid seaweed feed. A regular dose of fertilizer encourages thicker stems to form.

Don’t overfeed the plants after August.

Companion Planting

As we have already noted, these plants have a long growing season and can take up a lot of space. To make the most of the space between newly planted seedlings, you can plant  fast growing salad leaves. Salad crops, such as lettuce, typically have shallow roots that don’t compete with or disturb the more deeply rooted leeks. Harvest the salad leaves by midsummer because the growing leeks need as much space and light as possible. Harvesting also helps to improve air circulation, helping to keep plants healthy.

5 Salad leaves are good companions
Plant alongside fast growing, shallow rooted plants such as salad leaves.

You can also plant in combination with carrots, cabbage and beets. Carrots and leeks are a popular combination and protect each other from leek moth and carrot fly. Harvest the carrots before you begin blanching.

Avoid growing leeks close to peas and beans.

Blanching your Stems

While some varieties don’t require blanching most do. Depending on the variety you are growing you will need to blanch your stems around 2 to 3 weeks before harvesting.

Blanching increases the white, edible portion of the stem and also improves flavor. Without blanching leeks can taste harsh.

6 Blanch the stems
Blanching increases the white edible portion of the stem.

Depending on the variety, you can start blanching in mid august. This is a gradual process and best done in stages.

Blanching is not as complicated as it sounds. Simply mound up the earth around the stem as the plants grow. This prevents light from reaching the bottom part of the stem causing it to turn white. Be careful not to earth the soil too high or it may get stuck in the foliage. Mound the soil up by about 2 inches each time you blanch.

If you are growing in a trench or a pot, you can blanch your growing leeks by slowly filling the trench with soil to the bottom of the lowest leaf. Do this regularly until the plants stop growing. This is usually in mid to late fall depending on the variety and the weather.

Either method should give you 4 to 6 inches of blanched stem per plant.

Make sure the soil you are earthing up is dry and has a fine texture. Wet soil can cause rot while lumpy soil is difficult to handle and won’t block out the light.

You can also cover the stems with collars such as brown paper or plastic and clay piping. The collar should be at least 3 inches in diameter. This method is easier than mounding up the soil and ensures that the stem and foliage is kept soil and dirt free. Alternatively, to ensure that the stem is fully covered you can cover with a paper tube, such as the insert from a paper towel roll and then mound the soil around the tube. This prevents soil from getting trapped in the foliage. As the leek grows, the tube rots away.

Common Problems and How to Prevent Them

Leeks can suffer from all the usual onion family diseases.

Rust can cause orange spore patches to form on the leaf surface. While it isn’t deadly, rust can reduce the yield and is unsightly. If you dislike the appearance of the affected foliage it can be cut away.

Today many varieties are rust resistant. Correctly planting and spacing your crop, so that air can circulate between the plants, helps to deter rust. Frost also kills rust so it isn’t an issue for overwintering crops. If rust does strike, don’t grow leeks in the affected position the following year.

Onion fly, which causes foliage to yellow and droop, white rot and leek moth can also be problematic. White rot and downy mildew are easily prevented by correctly caring for crops and adopting a basic crop rotation system.

Young plants in particular are vulnerable to slugs and snails. Traps or biological controls can be used.

Harvesting your Plants

Depending on the variety you are growing you can harvest leeks from mid fall until late spring. Allow hardier varieties to remain in the ground until you are ready to use them.

Don’t try to pull the plant out of the soil. This can cause it to snap. Instead dig beneath the plant and lever it out with a spade or fork. When harvesting, lift the larger leeks first, allowing the smallest ones to remain in the ground and develop further.

If the soil is likely to be frozen for a while, lift leeks that are ready to use and store in sand in a cool place such as an unheated garage. They can be kept in this condition for about a month.

Excess leeks can also be stored on their side in a shady, shallow trench. Bury the leeks so that only the top part of the leaf stalk is above the ground. Lifting and reburying in this way helps to prevent plants from bolting. If you decide to keep your leeks in the ground, nip out flower stems. This encourages a leek bulb to form at the base of the plant. The bulb can be harvested in early summer for use as a substitute to onions or shallots.

Be careful not to leave your leeks in the ground for too long. Overly large specimens can lack flavor.

7 Resilient and low maintenance
Resilient and low maintenance, growing leeks is a great way to extend your growing season. 

Rich in nutrients, including calcium, potassium and vitamins A and C leeks are a great addition to the fall and winter vegetable garden. These resilient, easy to grow crops are a great way to extend your growing season and ensure a supply of fresh, homegrown vegetables throughout the year.

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