RHS Growing Guides
How to grow leeks
Our detailed growing guide will help you with each step in successfully growing Leeks.
Getting Started
These mildly flavoured members of the onion family, with their white stem bases (shanks) topped with a fountain of green leaves, are an attractive and popular crop to grow. Many varieties are hardy enough to stand up to the harshest weather without protection.
Leeks usually reach maturity after four or five months, in autumn and winter, when other fresh crops may be in short supply, and they don’t have to be harvested straight away. You can leave leeks standing through the colder months and lift plants whenever you want them. There are also early varieties for harvesting in summer, often before they reach full size, as sweet, tender baby leeks, ideal if you’re short on space or want quicker results.
You can harvest leeks at whatever size you wish. They have a delicious, sweet onion flavour. Baby leeks are tasty and tender, ideal for brazing, grilling or roasting, while mature leeks are hearty and bountiful – thinly slice, then sauté or steam, and use in casseroles, soups (leek and potato is a classic), stir-fries and many other dishes.
Month by Month
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Choosing
There are many leek varieties available, mainly varying in ultimate size, disease-resistance, hardiness and sowing/harvesting time. Early varieties can be lifted from late summer to autumn, mid-season varieties in winter, and late varieties into the following spring. Some are very tall, others short and stout. Some are hardier for winter use and colder locations, others have been bred for summer cropping as salad or baby leeks. There are even a few varieties with blue- or purple-tinted leaves for added ornamental appeal.
For consistent crops of tasty, high-quality leeks, it’s best to choose F1 hybrid varieties, and if you’ve had leek rust on your plot in the past, then select resistant varieties. Look too for varieties with an RHS Award of Garden Merit (AGM), which shows they performed well in trials – see our list of AGM fruit and veg for RHS-recommended varieties of leeks and many other crops.
You can see a wide range of crops, including leeks, growing in the veg plots at the RHS gardens, so do visit to explore how they’re grown, compare the varieties and pick up useful tips and inspiration.
What and where to buy
Leek seeds are widely available in garden centres and from online seed suppliers. Young plants may also be available in spring and early summer, from similar sources, although the choice of varieties will be much more limited.
Recommended Varieties
Leeks — winter & early spring
Stands well over a long period, good resistance to bolting and bulbing and some leek rust tolerance. Height 45cm (18...
Matures December onwards from a Spring sowing. Compact upright habit, good for smaller plots or growing space with good...
Early, high yielding premium F1 hybrid. Bulks up quickly and evenly. Blue/green foliage with long stems when well blanched.
Preparing the Ground
Choose a warm, sunny spot in well-drained soil, where you haven’t grown leeks or other members of the onion family for several years. Weed the ground thoroughly.
For a bumper crop, improve your soil by digging in two buckets of garden compost or well-rotted manure per square metre/yard, especially if you have lighter, free-draining soil.
Leeks don’t do well in very acidic soil (below pH 6), so if necessary reduce acidity by adding lime in autumn or winter.
Although leeks are best suited to growing in open ground or raised beds, you could plant several in a large, deep container filled with multi-purpose compost and positioned in a warm sunny spot.
Sowing
Sowing indoors
To get a head start and an earlier harvest, you can start leeks off indoors from late winter onwards on a warm windowsill or in a greenhouse, at temperatures above 7°C (45°F). This is also a useful option if you don’t have enough space outdoors in spring.
Fill small pots or modular trays with seed compost, water gently, then sow seeds thinly, 1cm (¾in) deep.
Keep the seedlings warm (at least 10°C/50°F) and in good light, and water regularly. Move into slightly larger pots if the roots appear from the drainage holes.
Young leeks are ready to be transplanted outdoors after about eight weeks, when 20cm (8in) tall, after the last frost. See Transplanting section below.
Sowing outdoors
The prime sowing months for leeks is March and April, either temporarily in a seedbed (for transplanting later – see below) or straight into their final position if you have space available. You can also sow later-cropping varieties in May and June, for harvesting in winter and spring, as well as fast-growing varieties for harvesting as baby leeks.
Prepare the ground as described above, then make a shallow drill about 1cm (¾in) deep and water along the base.
Sow leek seeds thinly, 1cm (½in) deep, in rows 20cm (8in) apart. See our guide to sowing outdoors and our guide to sowing veg seeds.
Cover early sowings with cloche or fleece if temperatures drop, as cold spells can cause plants to bolt.
After about two months, when the seedlings are 20cm (8in) tall, either transplant to their final position or thin out to their final spacing (see below), using the thinned leeks to make additional rows.
Transplanting
Young leeks grown in a seedbed, as well as those raised from seed indoors or bought as young plants, should be transplanted to their final growing site when about 20cm (8in) tall and pencil thick. Acclimatise indoor-grown plants to outdoor conditions first by hardening off.
Prepare the soil (see above) and water the plants well before transplanting:
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Make a row of holes with a large dibber or trowel handle, 15cm (6in) deep and 5cm (2in) across. Deep planting helps to form the long white shank
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Space the holes 15–20cm (6–8in) apart, depending on the variety, or 10cm (4in) apart for baby leeks. Allow 30cm (1ft) between rows
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Lift the young leeks from their seedbed or remove from their pot, then trim their roots with scissors to 2.5cm (1in) long
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Stand one leek in each hole, then fill the holes repeatedly with water. Called ‘puddling in’, this settles soil around the roots. There’s no need to backfill the holes
Alternatively, you can transplant leeks into large pots – up to six in a 40cm (16in) wide container filled with multi-purpose compost. Or for mini-leeks, which may be more successful in a container than full-sized leeks, space plants 10cm (4in) apart. Plant deeply, using the same method as for transplanting into the ground (above).
Plant Care
Watering
Water leek seedlings and young plants regularly until well established.
After that, you should only need to water during dry weather, repeating every couple of weeks until the next rainfall. Leeks growing in containers will need regular watering across the season, as the compost will dry out much more quickly.
Try to avoid overhead watering, as this can encourage fungal diseases such as leek rust.
Mulching
Apply a thick layer of mulch, such as well-rotted manure or garden compost, around leek plants to help hold moisture in the soil. This also helps to deter weed germination.
Weeding
Weed regularly so young leeks don’t have to compete for light, water and nutrients. Leek foliage casts little shade, so weeds grow readily around them and can soon swamp them, which will hinder their growth.
See our tips on controlling weeds.
Protecting from pests
Cover leeks with insect-proof mesh to deter leek moth and onion fly – see Problem solving section below.
Harvesting
You can harvest leeks at any size – baby leeks take only a couple of months, while large mature leeks can take four months or more. Start harvesting when they’re still quite small, usually from late summer, to extend the cropping period. If you harvest alternate leeks along the row, the rest can be left to grow larger. Gently lift individual plants from the soil using a fork.
Hardy leeks can remain in the ground through winter and into spring – just lift them whenever needed.
Before cooking, slice leeks lengthways and hold under running water to wash out any soil from between the layers of leaves.
Leeks have a sweet, mild onion flavour. Cook them gently, as they burn easily and turn bitter. These versatile veg can be steamed, sautéed or roasted, served with cheese sauce, made into leek and onion soup, or added to casseroles and many other dishes.
If your leeks start to bolt (flower), remove the stalk as soon as possible, while the bud is still green and tightly closed. These young flower buds, known as scapes, are delicious, either lightly cooked or raw, and have a very mild flavour, often likened to asparagus.
Problems
Leeks are relatively trouble free, although they can be affected by several fungal diseases, including leek rust and onion white rot, especially in damp conditions. Avoid planting leeks in soil that gets waterlogged.
Potential pests include leek moth, onion fly and allium leaf miner – if these are a problem, then grow leeks under insect-proof mesh. Slugs and snails may eat seedlings and young foliage.
Flowering (bolting) can be caused by low temperatures in spring, so cover early sowings with cloche or fleece. As soon as you spot a developing flower stalk, remove it, as it can turn the centre of the leek woody. If removed while still in tight bud, they are delicious lightly cooked.
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