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Entire healthy mature kohlrabi plant in a real garden bed, showing growth habit and scale.Primary identification image. 30–45 cm tall, 20–30 cm wide at maturity.

Kohlrabi

Brassica oleracea var. gongylodes L.

Also called: German turnip

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

A fast brassica grown for its swollen stem, ready in 6–8 weeks and best harvested small.

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Life cycle & growth stages

  1. 1. SeedSow 1 cm deep.
  2. 2. SeedlingEmerges in 5–8 days.
  3. 3. ThinningThin to 15–20 cm.
  4. 4. Stem swellingStem thickens above the soil.
  5. 5. Harvest readyBulb 5–8 cm.
  6. 6. HarvestCut below the bulb.

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

Planting calendar for Portland, Oregon

Start indoors 4–6 weeks before last frost; transplant 0–3 weeks before last frost; direct sow 2 weeks before to 2 weeks after last frost; 45–60 days to maturity from sowing. 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.

KohlrabiBrassica oleracea var. gongylodes
PlantStart indoorsDirect sowAutumn sowTransplantTendHarvest
KohlrabiFeb 22–Mar 8 (estimate)Mar 22–Apr 19 (estimate)Aug 27–Sep 10 (estimate)Mar 15–Apr 5 (estimate)Apr 19–Apr 29 (estimate)Apr 29–Jul 2 (estimate)
  • Start seeds indoors: Feb 22 – Mar 8
  • Transplant outdoors: Mar 15 – Apr 5
  • Direct sow: Mar 22 – Apr 19
  • Tend and monitor: Apr 19 – Apr 29
  • Harvest: Apr 29 – Jul 2
  • Autumn sowing: Aug 27 – Sep 10

Spacing & support

In-row 15–20 cm; rows 30–45 cm. Planner footprint: 1 cell of 30 cm, 4 plants per cell.

Side-profile diagram of mature kohlrabi: canopy 30–45 cm tall, 20–30 cm wide, medium root zone, support and harvest-access envelope.

Soil & water

Soil
Fertile loam
pH
6–7
Fertility
moderate
Water
Steady water prevents woody stems.
Frost
hardy; tolerates frost

Support & training

No support structure needed.

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

Harvest signs

  • Swollen stem 5–8 cm across
  • Harvest young for tenderness
Kohlrabi at harvest readiness, showing the visual cues: swollen stem 5–8 cm across; harvest young for tenderness.

Common problems

Pests: flea beetles, cabbage root fly, cabbage white caterpillars

Diseases: clubroot

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

Side-by-side: healthy kohlrabi leaf or fruit and an example of clubroot.

Container growing

  • Minimum 10 L (20 cm deep)
  • Use quality potting mix and water more frequently
Mature kohlrabi in a correctly sized container (10 L or more) with drainage visible.

Companion overview

2 reviewed relationship records (evidence: low).

Supported or conditional

None reviewed

Avoid or separate

None with evidence

Traditional claims only: Tomato.

1 popular pairing reviewed with no verified relationship.

Full companion profile

Crop rotation

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

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

Shared risks in Brassicaceae: clubroot, cabbage root fly, cabbage white caterpillars.

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 kohlrabi

Kohlrabi is one of the quickest brassicas and suits spring and autumn sowings. Harvest when the swollen stem is 5–8 cm across; larger bulbs turn woody, though some cultivars stay tender at a larger size.

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

Plants are small and can be spaced 15–20 cm apart, which makes kohlrabi a good filler between slower crops. It shares pests and clubroot with the rest of the cabbage family.

Two or more mature kohlrabi plants with a tape measure showing in-row spacing (15–20 cm).
Kohlrabi flower detail or bolting stage.
Immature swollen stem of kohlrabi developing on the plant.

Sow kohlrabi every three weeks in spring and again in late summer for a steady supply; purple cultivars are slower but stand longer without turning woody. Water evenly, because a check followed by rain splits the swollen stem. The leaves are edible and the plant is shallow enough to fit between taller crops.

Edible parts and safety

Edible: swollen stem, leaves.

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

Pests and diseases

Common pests: flea beetles, cabbage root fly, cabbage white caterpillars. Common diseases: clubroot. These vary by region; a photograph is an example, not a diagnosis. See the pest and disease guides and your local extension service.

flea beetles on kohlrabi, with a wider damage-context view.

Timeline

Season timeline for kohlrabi: sowing, transplanting, flowering, harvest and bed occupancy aligned to frost dates.Text alternative: Start seeds indoors Feb 22–Mar 8; Transplant outdoors Mar 15–Apr 5; Direct sow Mar 22–Apr 19; Tend and monitor Apr 19–Apr 29; Harvest Apr 29–Jul 2; Autumn sowing Aug 27–Sep 10.

Related plants

See also: Brassicaceae 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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