What Grows in Sioux City, Iowa

The last hard freeze (28°F) in Sioux City typically lands around Apr 19, 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 10.

The first hard freeze (28°F) in Sioux City typically arrives around Oct 17, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 3, so the watching starts about Sep 17 — about 181 days after the spring freeze cleared.

Measured between 28°F hard freezes, Sioux City sees about 181 frost-free days — roughly Apr 19 through Oct 17, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 10 to Oct 3, about 146 days.

The federal record around Sioux City is a meaningful one — 756 documented sites, mostly Underground Storage Tanks entries (337), the nearest Underground Storage Tanks record under a tenth of a mile 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 17 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 17 (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 17. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.