When to plant kohlrabi in USDA zone 6

Key dates for kohlrabi in zone 6

Dates are zone-wide averages. Local microclimates (south-facing slopes, urban heat, lakeside warmth, elevation) can shift the planting window by 1-2 weeks within the same zone.

Why this timing works for zone 6

Zone 6 has average annual minimum temperatures of -10 to 0°F and a 180-day frost-free window from mid- to late April to mid- to late October. Kohlrabi are hardy enough to handle light frost — and in fact prefer cool weather. They bolt or turn bitter once daytime temperatures consistently climb above 24 °C, which is why earlier is better in zone 6.

Kohlrabi is a fast-maturing brassica that tolerates light frost down to about -4 °C but turns woody and pithy when daytime temperatures exceed 27 °C; transplant or direct-sow 3–4 weeks before the last spring frost for a summer harvest, or time a second sowing so plants mature in the cool days of early autumn. Harvest promptly when the swollen stem reaches 5–7 cm (2–3 inches) in diameter — larger bulbs become fibrous. Succession-sow every 3 weeks to extend the harvest window.

Quick-grow guide

• Sun: Full sun — 6+ hours direct.
• Soil temperature for germination: 7-29 °C (45-85 °F).
• Spacing: 6-9 inches (15-23 cm) between plants.
• Days to harvest from transplant: ~55 days.
• Plant in cool weather and provide afternoon shade once temperatures climb above 24 °C.

Common mistakes — zone 6 × kohlrabi

• Planting before last frost: zone 6's last frost averages mid- to late April, and even a light frost will kill kohlrabi seedlings overnight.
• Skipping hardening off: even healthy indoor transplants need 7-10 days of progressive outdoor exposure before going in the ground.

Source and methodology

Frost-date averages from NOAA Climate Data Online within each USDA hardiness zone. Hardiness zone boundaries from the USDA Plant Hardiness Zone Map (2023). Crop timing offsets calibrated against US Cooperative Extension Service publications (UNL, UMN, NC State, Texas A&M, UF/IFAS) and cross-checked against the RHS sowing calendar for en-GB readers. Curated by the Growli editorial team.

Keep going

• How to grow kohlrabi — full guide
• USDA Zone 6 — frost dates and what else to plant
• All 13 USDA hardiness zones

Same crop, nearby zones

• When to plant kohlrabi in USDA zone 4
• When to plant kohlrabi in USDA zone 5
• When to plant kohlrabi in USDA zone 7
• When to plant kohlrabi in USDA zone 8

Other crops for zone 6

• When to plant tomatoes in zone 6
• When to plant peppers in zone 6
• When to plant basil in zone 6
• When to plant garlic in zone 6
• When to plant lettuce in zone 6
• When to plant bush beans in zone 6