How To Grow Leek From Seed

A stalwart, hardy and reliable winter vegetable plants, leek plants have many uses and taste great in everything from soups to pasta dishes. Their thick stems, known as shanks, have a versatile mild onion flavour and can be harvested when few other crops are still available. Seedlings thinned from the row even make an excellent salad vegetable.

Young leeks are often raised in a seed bed and then transplanted to their final growing positions. Their stems are blanched as they grow by regularly covering them with soil to make them white and tender. For really bumper crops, digging in plenty of garden compost or well-rotted manure in the autumn can improve the growing area.

To learn how to grow leeks from seed, read our detailed guide below, which features our experts’ best tips for growing these vegetable seeds to achieve wonderfully white stems.

You should choose a sunny spot with well-drained soil to give your leeks the best conditions for growing. Be sure to dig the soil over before planting leeks out, as leeks don't grow as well on compacted soil.

You should grow them in an area where you haven’t previously grown plants from the allium family (such as leeks, onion bulbs, shallot bulbs, and garlic bulbs), as this could increase the likelihood of disease.

You should sow leek seeds direct in the ground thinly in a seedbed, 1.5cm (half-inch) deep in rows 30cm (12in) apart from March to April. Afterwards, they are transplanted to the main growing area. This is done to save space in your garden and to give them the best chance of healthy growth in a controlled environment.

Thin seedlings to approximately 4cm (1.5in) apart when developed. The leek plants are ready to transplant to their final growing site from June when they are about 20cm (8in) tall and around the thickness of a pencil. Water well the day before lifting and transplanting. Prepare the plants by trimming off the root tips.

Make 15cm (6in) deep holes with a dibber. These holes should be 15cm (6in) apart in rows 30cm (12in) apart, then drop a plant into each hole. Fill the hole with water to settle the roots, and top up as necessary for the plants to establish.

Alternatively, leek seeds can be started indoors in trays of seed compost from January onwards, transplanting them outdoors when 20cm (8in) tall and after the last frost.

Growing Leeks in Containers

Leeks generally do better when grown in the ground, but they can be grown well in grow pots for those with limited space. They will still need a sunny spot with well-drained soil and a container with drainage holes to avoid waterlogging. They will need regular watering, as the soil is likely to dry out faster than when in the ground. Otherwise, the advice in this guide applies to container-grown leeks as it does to ground-grown leeks.

Earthing up

Keeping your leek plants blanched is essential to achieving the delicious white stems that they are characteristically known for. You should therefore gently mound up the dry soil around the plants to shield them from sunlight. This will prevent them from turning green, keep them white and tender and increase stem length. This also helps to keep your plants stable and protected from wind.

Watering

You should top up younger plants with water as necessary. Once established, leeks should be watered only when needed, specifically during dry spells. As mentioned above, leeks grown in containers will need more frequent watering as the soil can be prone to drying out quickly.

Weeding

You should keep your growing area weed-free, as this will prevent your leeks from competing for resources. Be careful around the stems, an onion hoe or a narrow draw hoe will help to prevent damage to them. Don't allow soil to fall between the leaves when weeding, as this will make for gritty stems when harvested.

Unlike some other plants, leeks do not produce thick foliage that overshadows weeds once established. As a result, managing weeds effectively throughout their growth is important for their success.

Mulching

A good layer of fertiliser or well-rotted manure will help plants reach their full potential by providing the nutrients they need. In addition, this can help to prevent weed growth and keep the soil beneath moist.

Growing leeks doesn’t usually pose too many problems, though there are one or two issues that have been known to affect plants. Below are the most common problems and methods on how to prevent or resolve them:

• Diseases - Leeks can suffer from soil-borne diseases, such as leek rust and onion white rot. The best method of dealing with these is prevention, so growing in well-drained soil that avoids the damp conditions these thrive in is important.
  
  It is also advisable to rotate crops, growing them in a different location every year. This means you should also avoid growing any other plants from the allium family consecutively to avoid problems.
  
  There are disease-resistant vegetable seeds that can prevent issues; Leek Oarsman F1 is highly recommended.
• Pests - Leeks can be prone to certain pests, such as allium leaf miner, onion fly and leek moth. So, using pest and disease control products such as garden netting can prevent these from attacking your plants. Using a leek moth trap can be useful to indicate whether your plants will be susceptible to attacks and do require netting.
• Bolting - If experiencing low temperatures while young, leek plants can sometimes bolt. This can be prevented by keeping them warm during colder periods, specifically in early spring, with fleece or garden cloches. Any flower stalks should be removed as soon as you spot them to prevent stems from turning woody.

Customer Tips

We conducted a survey to find out what our customers’ best advice is for growing leeks successfully. These tips can be found in our catalogues, but we’ve included them here to provide you with some extra information to take on board.

We haven’t tried out all of the tips below, but they provide insight into how others sow and grow their leeks that may come in handy.

• Using a polytunnel - Sow seeds in a large (8-9") pot of compost in a cold frame or polytunnel for early germination and to avoid taking up space in the border. Then, plant out in the final position when large enough.
• Using toilet roll inserts - Sow in a seed tray to propagate, and once sturdy, transplant into a deep trough and leave until pencil thick. When at this stage, transplant into prepared ground. Use a bulb planter to make a hole 6in deep, put the cardboard insert from a toilet roll into the hole, trim off roots to 1/2in and leaves of leeks so that the leeks are approx. 8-10in tall, and then place into the toilet roll insert. Fill with water. Once leeks grow, bank them up with soil. The cardboard toilet roll inserts will disintegrate into the ground.
• Christmas sowing - Start them off in seed trays on Christmas Day. Then when large enough, transplant into pots until they are fairly thick, then bore a hole with a crowbar about 6in deep and drop the plant in and just water it. God will fill the hole in.
• Leek moth - Start the seeds as early as the weather allows. Leek moth is the worst thing to contend with, but if you get an attack, then just cut the leeks down to almost ground level. You will be amazed at how they will recover.
• Using quality soil - For good size leeks, give them good soil and take care of them. If they are just stuck in anywhere in the garden or on the allotment, they don't grow to a decent size.