USDA Zone 4 planting calendar
When to plant summer squash 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 summer squash in zone 4
| Stage | When | Anchor |
|---|---|---|
| Indoor seed start | late April (April 24) | 3 weeks before last frost |
| Outdoor transplant | late May (May 29) | 14 days after last frost (mid-May) |
| First harvest (estimate) | late July (July 23) | ~55 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. Summer squash 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.
Summer squash (zucchini, yellow crookneck, pattypan) wants the same warm soil as cucumbers — 18 °C minimum at sowing depth. A single plant can outproduce a small family once it gets going, so don't over-plant.
Quick-grow guide
- Sun: Full sun — 6-8 hours direct.
- Soil temperature for germination: 21-29 °C (70-85 °F).
- Spacing: 24-36 inches (60-90 cm) between plants.
- Days to harvest from transplant: ~55 days.
- Wait until night temperatures stay above 10 °C — cold soil stunts warm-season crops permanently.
Common mistakes — zone 4 × summer squash
- Skipping indoor seed-starting: zone 4's 125-day season is too short for summer squash from direct sow — you need transplants 3+ 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 summer squash — full guide
- USDA Zone 4 — frost dates and what else to plant
- All 13 USDA hardiness zones
Same crop, nearby zones
- When to plant summer squash in USDA zone 3
- When to plant summer squash in USDA zone 5
- When to plant summer squash in USDA zone 6