How to Grow Kohlrabi: Planting, Spacing, Care & Harvest

Quick answer

Start indoors 4–6 weeks before transplanting; set out 4 weeks before last frost (UNH, transplant −4). UMN: seed ¼–½ inch deep; thin or space about 4 inches. Ideal weather about 65–75°F. Harvest swollen stems around tennis-ball size before woody. Fall direct seed in July in Minnesota (UMN calendar — not a first-frost week count).

Kohlrabi at a glance

PlantStart indoors: 10–8 wk before last frost; Transplant: 4 wk before last frost
WaterAbout 1 inch of water per week.
SpacingUMN: seed ¼–½ inch deep; thin or space about 4 inches in spring.
Days to harvest50 (CSU)
-11-10-9-8-7-6-5-4-3-2-1LF+1+2+3
■ Start indoors   ■ Plant out   ■ Harvest
Weeks relative to last frost (LF). Colored weeks show when our ZIP planner schedules each step.
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Updated

Planting dates for your ZIP: the ZIP planting planner counts each window from your local frost dates.

Organic pests and diseases: see also organic pest control. Use any product as the label directs.

Kohlrabi plants with swollen stems
Kohlrabi (Brassica oleracea Gongylodes group). Photo: unknown author, Wikimedia Commons, CC0 (resized).

Planting timing

UNH: seed to transplant 4–6 weeks; set out 4 weeks before last frost. (UNH when to plant) Planner: Start indoors last frost −10 to −8; Transplant last frost −4. UMN: start indoors 4 to 6 weeks before transplanting; spring direct seed mid-April–early May in Minnesota; avoid planting after May 1 for quality; fall direct seed in July (MN calendar — not a sourced first-frost week). (UMN kohlrabi)

Depth and spacing

UMN: seed ¼–½ inch deep; thin or space about 4 inches in spring. Use a lightweight row cover in the first weeks for flea beetles (UMN).

Sun, soil and water

Cool weather about 65–75°F is ideal; fertile, moisture-retentive loam (UMN). About 1 inch of water per week. Rotate about 4 years off related Brassicas. Prefer compost and a soil test; we omit printed synthetic side-dress rates.

Care

Hardening: protect from nights below 40°F; prolonged nights below 50°F or late frosts may cause bolting (UMN).

Harvest

Many planning tables list about 50 days. Harvest swollen stems about tennis-ball size before they turn woody (UMN). Fall crops can run larger with less fiber risk (UMN). Refrigerated quality about 2 weeks (UMN).

Pests and diseases

Flea beetles, cabbageworms/loopers/diamondback moth, cabbage maggot, swede midge; Alternaria, black rot, black leg, clubroot (UMN). Cultural: lightweight row cover first weeks; radish trap crop for flea beetles; clean seed; 4-year rotation (UMN kohlrabi; UMN flea beetles).

Related: ZIP planner · organic pest control · turnips · all grow guides

Frequently asked questions

When do I transplant kohlrabi?

About 4 weeks before last frost (UNH). Start indoors 4–6 weeks before that transplant date.

When is the fall crop?

UMN lists July direct seed for Minnesota — a regional calendar, not a sourced first-frost week count.

Why did my kohlrabi bolt?

UMN: late frost or a week or more of nights below 50°F can trigger bolting.

More grow guides: All grow guides

Sources