How to Grow Three-cornered Leeks
On this page
Three-cornered leeks (Allium triquetrum) — herbaceous perennial.
Unlike an annual crop, the work here is front-loaded into establishment: get the planting and the site right and the same plants crop for several seasons.
Core growing advice on this page is checked against named horticultural sources — see References.
Three-cornered Leek (Allium triquetrum)
7 sources cited · Verified
Growth Stages
| Stage | BBCH | Notes |
|---|---|---|
| Planting or division | 0 | Bulbs planted fairly deeply (PFAF). Propagate by seed, sown as soon as ripe in a greenhouse or cold frame -- germinates quickly -- or by division in summer after the plant has died down, with divisions replanted straight into their permanent position. NOTE: illegal to plant or cause to grow in the wild in Great Britain (RHS, Schedule 9) -- confine to a contained garden setting only, and check local regulations elsewhere. |
| Leaf growth | 3 | RHS: in leaf from February to July, narrow green leaves on distinctively triangular (three-cornered) stalks. |
| Flowering | 6 | RHS: in flower from spring to early summer, drooping white bell-shaped flowers with a central green vein on each petal. |
| Harvest & spread control | 8 | Bulbs harvested early summer, store at least six months; leaves and flowers picked while present. RHS/PFAF both note vigorous spread by seed and bulbils -- vigilant deadheading is recommended to prevent unwanted colonisation, and is a legal necessity, not just tidiness, given the Schedule 9 restriction. |
Quick Facts
| Factor | Value |
|---|---|
| Soil texture | Chalk, clay, loam or sand (RHS) |
| Drainage | Moist but well-drained |
| Lifecycle | herbaceous perennial |
| Edible parts | bulbs, leaves, flowers |
At a Glance
Harvest & Storage
When to pick: Bulbs (up to 20mm across) are harvested in early summer and store for at least six months (PFAF, tier 2). Leaves can be picked as a leek substitute at any point while present -- younger leaves raw, mature leaves cooked. Flowers are picked fresh for use as a garnish.
Diseases
Pests
Three-cornered Leek, Flower to Colony
Plan your Three-cornered Leeks planting
Timing for Three-cornered Leeks follows soil temperature and frost, not the calendar date. The Global vegetable planting calendar explains the method. To work out where it fits in your beds, sketch your plot in the free Garden Layout Planner.
Growing Three-cornered Leek in another region
Sowing dates, frost timing and local advice differ by country. Use the guide for where you garden.
Sources
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Listed under Schedule 9 of the Wildlife and Countryside Act in England and Wales, making it "an offence to plant or otherwise cause to grow this species in the wild". Identification: uniquely TRIANGULAR stem, which gives the plant its name; narrow three-angled strap-like leaves in basal clusters; small white star-shaped flowers in umbels April to June; garlic or onion scent when bruised. Spreads both by seed (wind, water, human activity) and vegetatively by bulb division, enabling rapid colonisation. DISPOSAL: because it is Schedule 9 listed, all plant material and associated soil that may contain seeds or bulbs is classed as CONTROLLED WASTE and can only be removed by a licensed contractor to an authorised waste facility.
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A compiled plant-use reference rather than a university or government body. Used only for cultivation detail RHS's weeds-focused page does not cover. Bulbs planted fairly deeply. Seed sown as soon as ripe in a greenhouse or cold frame, germinates quickly; or divide in summer after the plant has died down, replanting divisions directly into their permanent position. Bulbs up to 20mm, mild garlic flavour, harvested early summer, store at least 6 months; leaves used raw or cooked as a leek substitute; flowers "juicy with a mild garlic flavour", used as a garnish. Reader reports describe it colonising large areas even from careful initial planting -- consistent with RHS's own Schedule 9 listing -- and recommend vigilant deadheading to prevent unwanted spread.
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PFAF entry for Allium triquetrum. Fetched and parsed directly for the USDA hardiness rating.
These 3 sources are specific to this region. The full list of 7 sources behind this guide (Environet UK, Plants For A Future (PFAF), Royal Horticultural Society) is in the references of our UK guide to three-cornered leeks; they describe the plant itself, which is the same wherever it grows.
Frequently Asked Questions
What problems affect three-cornered leeks?
Our data links 1 disease and 1 pest to this crop. See the sections above for each one and how to manage it.
Plan next season before the problems start
This page gives you the thresholds; the planner turns them into your own calendar. It works from what you can observe and measure in your garden rather than from dates written for somebody else’s latitude.
Get the Global Garden Planner →Instant PDF download · Works in either hemisphere
How this guide is put together
The growing data on this page — sowing windows, pests, diseases, soil and site requirements — comes from named horticultural sources, listed in References below, checked against international horticultural research and extension sources. An automated pipeline assembles that verified data into the page you're reading: it selects which facts to lead with and builds the surrounding prose and layout. It does not invent a date, a source or a number — where a verified value for a field isn't available, the page leaves it out rather than guessing. A person reviews and publishes each page; nothing goes live unverified.
Last verified 2026-09-02
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Where To Go From Here
Take this crop from reading into a written plan for your own beds.
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Plan the next step
Use the printable SoilCommander planner for your region to turn this guide into sowing dates, bed layouts and weekly garden tasks.