When to plant summer squash & zucchini in Madison, Wisconsin
May 15 – May 29
Transplant outdoors · typical Madison yearClimate basis: NOAA station Uw Arboretum - Madison, WI (USC00470273), 4 mi (6 km) from downtown Madison (ZCTA 53703 centroid), elevation 870 ft, on the 1991–2020 climate normals. Transplant summer squash & zucchini outdoors from approximately the dates above, anchored to the median last spring 32°F freeze (May 1). One year in ten still freezes after May 17.
The Madison year
- indoors under lights
- in the garden
- frost-free season
- 1-in-10 years still freeze to May 17
Every method, with its sources
Start seeds indoors
Apr 17 – Apr 24Sow in pots 3–4 weeks before the outdoor window opens (UNH 3–4 weeks; Missouri G6570 3–5 weeks). Anchored to the median last spring freeze (May 1). University of New Hampshire Extension · University of Missouri Extension
Transplant outdoors
May 15 – May 29UNH: set out 2 weeks after last frost; Purdue very-tender class agrees. Anchored to the median last spring freeze (May 1). University of New Hampshire Extension · Purdue University Extension
Direct-sow outdoors
May 15 – May 29Purdue: very tender — at least two weeks after the average last frost. Penn State earliest sowing May 15 (+14 days) agrees. Anchored to the median last spring freeze (May 1). Purdue University Extension · Penn State Extension (York County Master Gardeners)
Variety assumption: Assumes an average zucchini-type variety (about 50–60 days from seed; Penn State lists 60).
These windows describe typical years (1991–2020 climate normals), not this year's forecast. Freezes happen outside them — especially in frost pockets, valleys, and urban edges. Watch the forecast before committing tender plants.
Crop rule sources (4)
- University of New Hampshire Extension: Growing Vegetables: When to Plant Your Vegetable Garden [fact sheet] (accessed 2026-07-24)Per-crop 'time from seed to transplant' and 'safe to set out in garden' relative to last frost.
- University of Missouri Extension: Starting Plants Indoors from Seeds (G6570) (accessed 2026-07-24)Weeks needed to grow vegetable transplants indoors (Table 2).
- Purdue University Extension: Indiana Vegetable Planting Calendar (HO-186-W) (accessed 2026-07-24)Hardiness classes: hardy = plant 4-6 wk before last spring frost; semi-hardy = 2-4 wk before; tender = after average last frost; very tender = at least 2 wk after. Table 2: fall planting at least 4-8 wk before first fall frost.
- Penn State Extension (York County Master Gardeners): Vegetable Seed Planting Guide (accessed 2026-07-24)Earliest/latest sowing dates for a May 1 last-frost / Oct 1 first-frost baseline; offsets derived by date difference from May 1. Also days-to-maturity figures.