What Grows in Sun Prairie, Wisconsin

The last hard freeze (28°F) in Sun Prairie typically lands around Apr 16, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about May 7.

The first hard freeze (28°F) in Sun Prairie typically arrives around Oct 18, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 4, so the watching starts about Sep 18 — about 185 days after the spring freeze cleared.

Measured between 28°F hard freezes, Sun Prairie sees about 185 frost-free days — roughly Apr 16 through Oct 18, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 7 to Oct 4, about 150 days.

The federal record around Sun Prairie is a meaningful one — 1,217 documented sites, mostly Underground Storage Tanks entries (717), the nearest Underground Storage Tanks record about 0.1 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.

From about Sep 18 the job here turns from planting to protecting — the last start even a 30-day crop can finish. As the season closes around the first 28°F hard freeze near Oct 18 (NOAA 1991–2020 climate normals), three moves buy time: row cover or an old sheet over tender plants on still, clear nights; water the soil the afternoon before a freeze, so it holds warmth overnight; and harvest tomatoes, peppers and basil before Oct 18. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.