What Grows in Mountain Plains, South Dakota

The last hard freeze (28°F) in Mountain Plains typically lands around May 3, 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 24.

The first hard freeze (28°F) in Mountain Plains typically arrives around Oct 8, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 24, so the watching starts about Sep 8 — about 158 days after the spring freeze cleared.

Measured between 28°F hard freezes, Mountain Plains sees about 158 frost-free days — roughly May 3 through Oct 8, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 24 to Sep 24, about 123 days.

The federal record around Mountain Plains runs heavier than most — 318 documented sites, mostly Nitrate entries (186), the nearest Nitrate record about 0.5 miles out — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.

From about Sep 8 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 8 (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 8. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.