When to plant broccoli in USDA zone 1

Key dates for broccoli in zone 1

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 1

Zone 1 has average annual minimum temperatures of -60 to -50°F and a 60-day frost-free window from mid-June to mid-August. Broccoli 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 1.

Start seeds indoors 6–8 weeks before last frost; transplant outdoors 2–4 weeks before last spring frost when soil reaches at least 7 °C (45 °F). Mature plants withstand temperatures as low as −6 °C (21 °F). Heads button (form premature small curds) when exposed to temperatures below 10 °C (50 °F) for extended periods as young seedlings, so harden off carefully. In zones 8–10, a second crop is practical as a fall planting, set out in late summer for harvest before hard freezes.

Quick-grow guide

• Sun: Full sun — 6+ hours direct.
• Soil temperature for germination: 7–29 °C (45–85 °F).
• Spacing: 18–24 inches (45–60 cm) between plants.
• Days to harvest from transplant: ~80 days.
• Plant in cool weather and provide afternoon shade once temperatures climb above 24 °C.

Common mistakes — zone 1 × broccoli

• Planting before last frost: zone 1's last frost averages mid-June, and even a light frost will kill broccoli 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 broccoli — full guide
• USDA Zone 1 — frost dates and what else to plant
• All 13 USDA hardiness zones

Same crop, nearby zones

• When to plant broccoli in USDA zone 2
• When to plant broccoli in USDA zone 3

Other crops for zone 1

• When to plant garlic in zone 1
• When to plant lettuce in zone 1
• When to plant peas in zone 1
• When to plant carrots in zone 1
• When to plant cauliflower in zone 1
• When to plant cabbage in zone 1