What Grows in Oak Brook, Illinois

The last hard freeze (28°F) in Oak Brook typically lands around Apr 5, 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 Apr 26.

The first hard freeze (28°F) in Oak Brook typically arrives around Nov 4, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 21, so the watching starts about Oct 5 — about 213 days after the spring freeze cleared.

Measured between 28°F hard freezes, Oak Brook sees about 213 frost-free days — roughly Apr 5 through Nov 4, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 26 to Oct 21, about 178 days.

The federal record around Oak Brook is a meaningful one — 4,745 documented sites, mostly Underground Storage Tanks entries (2,306), the nearest PFAS 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 Oct 5 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 Nov 4 (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 Nov 4. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.