Leeks are one of the most dependable winter crops on an allotment. They’re hardy, low-maintenance, and ideal for keeping beds productive when most vegetables have finished for the year. With a long growing season and a bit of early preparation, you can harvest strong, thick stems from autumn right through to spring. This guide covers everything you need to know to grow leeks successfully from seed to harvest.
Quick Facts
| Metric | Details |
|---|---|
| When to Sow | January to April (indoors) / March to April (outdoors) |
| Germination Time | 10–21 days |
| Time to Harvest | 25–40 weeks |
| Ideal Soil | Fertile, well-drained, moisture-retentive |
| Position | Full sun |
| Spacing | 15cm apart, 30cm between rows |
Preparing the Soil
Leeks like rich, moisture-retentive soil.
Incorporate plenty of compost or well-rotted manure into the bed the previous autumn or winter.
Avoid freshly manured soil right before planting — it can cause lush growth and weak stems.
Aim for a fine, crumbly texture to make transplanting easier.
Sowing the Seeds
You can sow leeks indoors from January or directly outdoors from March.
Sowing Indoors (recommended)
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Fill seed trays or modules with compost
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Sow thinly, covering lightly
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Keep at 15–20°C until germinated
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Once seedlings reach pencil thickness, they’re ready to transplant
Direct Sowing
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Sow thinly into drills 1cm deep
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Keep moist
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Thin seedlings gradually as they grow
Indoor sowing gives stronger, more uniform plants.
Transplanting Leeks
Transplant when seedlings reach about 20cm tall and are roughly the thickness of a pencil.
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Make holes 15cm deep using a dibber.
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Drop one seedling into each hole.
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Do not fill the hole with soil — simply water it in.
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The soil naturally washes in over time, helping blanch the stem.
This method produces the classic long white shanks leeks are known for.
Watering and Feeding
Leeks need steady moisture to bulk up properly.
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Water deeply in dry spells
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Mulch around plants to conserve moisture
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Feed with a general-purpose fertiliser or liquid seaweed every few weeks during summer
Avoid overfeeding with nitrogen — it encourages soft growth susceptible to disease.
Maintenance and Care
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Remove weeds regularly
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Hill up soil around stems in late summer to improve blanching
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Inspect for leek moth damage (more on this below)
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In exposed allotments, windbreaks help protect taller varieties
Leeks are naturally hardy and tolerate frost extremely well.
Harvesting
Leeks are ready when stems reach a good thickness — typically from October onwards.
Use a fork to gently lift them from the soil, avoiding damage to neighbouring plants.
They can remain in the ground until early spring, making them an excellent winter standby.
For storage, trim roots and leaves and keep them in a cool shed or fridge for up to two weeks.
Common Problems and Solutions
| Problem | Cause | Solution |
|---|---|---|
| Leek moth | Larvae tunnelling into stems | Use insect mesh; remove infested leaves; rotate beds |
| Rust (orange spots) | Fungal disease in warm, humid weather | Space plants well; remove affected leaves; choose resistant varieties |
| Thin stems | Crowding, poor soil, drought | Improve soil fertility; water consistently; thin properly |
| Splitting stems | Irregular watering | Keep soil evenly moist |
Companion Planting Tips
Leeks grow well with:
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Carrots (mutual pest deterrent)
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Celery
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Onions
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Beetroot
Avoid planting near beans or peas — they can stunt each other’s growth.
Leeks also work brilliantly as part of a traditional allium bed rotation.
Using the Allotment Planner Tool
Add leek rows to the Allotment Planner tool to space your transplant holes accurately and position them within your crop rotation schedule.
You can also track sowing dates, transplanting, and expected harvest windows to keep your winter veg organised.
FAQs
When should I transplant leeks?
When seedlings are around 20cm tall and pencil-thick.
How long do leeks take to grow?
Between 25 and 40 weeks, depending on variety and sowing time.
Do leeks survive frost?
Yes — they’re extremely hardy and grow through winter.
Why are my leeks skinny?
Usually overcrowding, lack of nutrients, or insufficient watering.
What’s the best leek variety to grow?
‘Musselburgh’, ‘Porbella’, and ‘Autumn Giant’ are reliable UK favourites.