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Entire healthy mature leek plant in a real garden bed, showing growth habit and scale.Primary identification image. 45–60 cm tall, 10–15 cm wide at maturity.

Leek

Allium ampeloprasum (Porrum Group) L.

Family
Amaryllidaceae
Season
Cool-season biennial grown as an annual
Best grown in
Portland, Oregon

A slow, very hardy allium transplanted in late spring and harvested from autumn through winter.

Safety: Toxic to dogs and cats.

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Life cycle & growth stages

  1. 1. SeedSow indoors in late winter.
  2. 2. SeedlingGrass-like seedlings; grow to pencil thickness.
  3. 3. TransplantDrop into 15 cm holes, water in.
  4. 4. Mid-growthShanks thicken through summer.
  5. 5. Harvest readyShank 2–4 cm.
  6. 6. HarvestLift with a fork through winter.

Growth stages are ordered chronologically; timing varies with cultivar, temperature, light and care.

Planting calendar for Portland, Oregon

Start indoors 8–10 weeks before last frost; transplant 2 weeks before to 2 weeks after last frost; 100–150 days to maturity from transplant. Windows are derived from the region's average frost dates (last Apr 5, first Nov 5) and are estimates until you confirm your own dates in the calendar.

LeekAllium ampeloprasum (Porrum Group)
PlantStart indoorsDirect sowAutumn sowTransplantTendHarvest
LeekJan 25–Feb 8 (estimate)——Mar 22–Apr 19 (estimate)Apr 19–Jun 30 (estimate)Jun 30–Dec 9 (estimate)
  • Start seeds indoors: Jan 25 – Feb 8
  • Transplant outdoors: Mar 22 – Apr 19
  • Tend and monitor: Apr 19 – Jun 30
  • Harvest: Jun 30 – Dec 9

Spacing & support

In-row 15–15 cm; rows 30–40 cm. Planner footprint: 1 cell of 30 cm, 6 plants per cell.

Side-profile diagram of mature leek: canopy 45–60 cm tall, 10–15 cm wide, medium root zone, support and harvest-access envelope.

Soil & water

Soil
Deep, fertile loam
pH
6–7
Fertility
high
Water
Regular water in dry spells.
Frost
very hardy; tolerates frost

Support & training

No support structure needed.

Leek mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Harvest signs

  • Shank 2–4 cm thick
  • Lift as needed from autumn onward
Leek at harvest readiness, showing the visual cues: shank 2–4 cm thick; lift as needed from autumn onward.

Common problems

Pests: leek moth, onion fly, thrips

Diseases: rust, white rot

Appearance alone is not a diagnosis; confirm with a regional extension guide.

Side-by-side: healthy leek leaf or fruit and an example of rust.

Container growing

  • Minimum 15 L (30 cm deep)
  • Use quality potting mix and water more frequently
Mature leek in a correctly sized container (15 L or more) with drainage visible.

Companion overview

1 reviewed relationship record (evidence: low).

Supported or conditional

None reviewed

Avoid or separate

None with evidence

1 popular pairing reviewed with no verified relationship.

Full companion profile

Crop rotation

Avoid planting leek or other onion family crops in the same spot for 3 years. Rotation is about previous seasons, not about live neighbours.

Year 1Year 2Year 3AmaryllidaceaeOther familyOther familyback after 3+ years

Shared risks in Amaryllidaceae: onion white rot, downy mildew, onion fly.

Crop rotation hub

Sources, reviewer & update

Sources

Reviewer: Garden Planner editorial team (pending independent horticultural review)

Last reviewed: August 15, 2026 · version 1

Found an error or have feedback? Let us know.

Growing leek

Leeks are sown indoors in late winter and transplanted when pencil-thick, dropped into 15 cm holes and watered in rather than backfilled, which blanches the shanks. They need 100–150 days and stand in the ground through frost, to be lifted as needed.

Leek seed beside a ruler or coin for scale.
Leek seedling at cotyledon and first-true-leaf stage, in soil, distinguishable from common weeds.
Leek mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Leeks are upright and narrow, so they fit between other crops, but they are shallow-rooted and dislike weed competition. Leek moth and rust are the main problems; rotate with other alliums.

Two or more mature leek plants with a tape measure showing in-row spacing (15–15 cm).
Leek flower detail or bolting stage.
Immature stem of leek developing on the plant.

Edible parts and safety

Edible: stem (shank), leaves. Toxic to dogs and cats.

Hands or tool harvesting leek correctly (cut, pull, twist or pick) without damaging the plant.

Pests and diseases

Common pests: leek moth, onion fly, thrips. Common diseases: rust, white rot. These vary by region; a photograph is an example, not a diagnosis. See the pest and disease guides and your local extension service.

leek moth on leek, with a wider damage-context view.

Timeline

Season timeline for leek: sowing, transplanting, flowering, harvest and bed occupancy aligned to frost dates.Text alternative: Start seeds indoors Jan 25–Feb 8; Transplant outdoors Mar 22–Apr 19; Tend and monitor Apr 19–Jun 30; Harvest Jun 30–Dec 9.

Related plants

See also: Amaryllidaceae family page · crop rotation · regional calendar · guides

Our Methodology & Sources

We synthesize peer-reviewed research, university extension publications, and trusted horticulture resources. Our evidence levels help you understand how strong the science is behind the guidance.

Evidence tiers

Supported evidenceConsistent results from multiple robust studies
Traditional claimHistorical use reported, limited scientific support
Context dependentMixed or variable results across conditions
No verified relationshipNo reliable evidence identified

Primary source types

  • Peer-reviewed journal articles
  • University extension publications
  • Government & research institute reports
  • Systematic reviews & meta-analyses

Last updated

August 24, 2026

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