USDA Zone 4 planting calendar
When to plant basil in USDA zone 4
Sowing, transplant, and harvest dates calibrated to zone 4's 125-day season (Northern Maine, northern Wisconsin, Montana, parts of New England).
Key dates for basil in zone 4
| Stage | When | Anchor |
|---|---|---|
| Indoor seed start | early April (April 3) | 6 weeks before last frost |
| Outdoor transplant | late May (May 22) | 7 days after last frost (mid-May) |
| First harvest (estimate) | late July (July 21) | ~60 days from transplant |
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 4
Zone 4 has average annual minimum temperatures of -30 to -20°F and a 125-day frost-free window from mid-May to mid-September. Basil are tender — they need soil above 16 °C to grow and stop fruiting once nights drop below 10 °C. That puts the safe outdoor planting window after the last spring frost passes, and the harvest closes when fall temperatures arrive.
Basil is one of the most cold-sensitive common herbs — it sulks below 10 °C and dies in light frost. Wait a full week after the last spring frost before moving transplants outside, or direct-sow two weeks after frost when soil hits 18 °C.
Quick-grow guide
- Sun: Full sun — 6+ hours direct.
- Soil temperature for germination: 20-25 °C (68-77 °F).
- Spacing: 8-12 inches (20-30 cm) between plants.
- Days to harvest from transplant: ~60 days.
- Wait until night temperatures stay above 10 °C — cold soil stunts warm-season crops permanently.
Common mistakes — zone 4 × basil
- Skipping indoor seed-starting: zone 4's 125-day season is too short for basil from direct sow — you need transplants 6+ weeks ahead of last frost.
- Moving transplants out before soil hits 16 °C — cold roots stall growth for weeks even after the air warms up.
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 basil — full guide
- USDA Zone 4 — frost dates and what else to plant
- All 13 USDA hardiness zones
Same crop, nearby zones
- When to plant basil in USDA zone 3
- When to plant basil in USDA zone 5
- When to plant basil in USDA zone 6