Duncan, Oklahoma, sits in USDA hardiness zone 8a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Among the crops suited to this profile: cabbage, fig, california poppy, and collard greens. The site-level story — soil, sun, drainage — decides the rest.
Even in Duncan, no two yards are alike.
A low spot, a south-facing slope, or a stand of trees moves the frost date and sun across a single Duncan lot. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Duncan — soil, climate, flood, and parcel records. How we handle your address.
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Duncan — the short answer
Duncan, Oklahoma: USDA zone 8a, about 252 days between hard freezes, across 27K acres of city.
- USDA zone
- 8a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 13
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Nov 20
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~252
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 27K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are this town’s own 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 8a is Duncan's average, not your lot's — a low corner or a tree line moves it. Against Duncan's 252-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Duncan
Each reading below is measured for Duncan itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredDuncan runs about 252 days between hard freezes — a long growing season.
There is slack for succession plantings and slow-finishing crops: many vegetables can be sown twice, and the heat-lovers have time to ripen fully.
Plan a second sowing of quick crops after the first comes out, and use the fall window most gardeners let sit idle.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredDuncan sits in USDA hardiness zone 8a.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country Duncan is in
Duncan sits in the Cross Timbers — EPA Level III, inside the wider Great Plains. That is read at Duncan's own centroid rather than borrowed from Stephens County.
What Grows in Duncan
Every plant below cleared Duncan's own zone 8a and its 252-day season. Each card opens that plant's Oklahoma profile. How we score.
Is it too late to plant in Duncan?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Feb 13; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 13 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 20 — long-season crops need about 90 days of runway, quick greens only 30. A long window like this one runs successions deep into fall — and even its last weeks take quick greens and garlic.
What's on the federal record near Duncan
Closest first, within ~10 miles of Duncan. Listing isn't leaking, and distance isn't exposure.
- Halliburton Services AviationUnderground Storage Tanks · 1100 ft
- City Of DuncanUnderground Storage Tanks · 1600 ft
- Halliburton Plant IiUnderground Storage Tanks · 2000 ft
- Okla Dept Of TransportationUnderground Storage Tanks · 2100 ft
- HALLIBURTON ENGRY SVCS - PLANT 2Brownfields · 2100 ft
- Carpet OutletUnderground Storage Tanks · 2300 ft
- Tubbs AviationUnderground Storage Tanks · 2600 ft
- ASAP General StoreUnderground Storage Tanks · 0.5 mi
- Halliburton Services MrdUnderground Storage Tanks · 0.6 mi
- Duncan Coca-ColaUnderground Storage Tanks · 0.6 mi
- Halliburton Services Res. CenUnderground Storage Tanks · 0.7 mi
- DUNCAN ARMORYBrownfields · 0.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Duncan's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near Duncan.
Total Sites
186
within ~10 miles of Duncan
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
within ~10 miles of Duncan
Severity Distribution
within ~10 miles of Duncan
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Duncan, two things run higher than the national average within ~10 miles of Duncan — Toxics Release Inventory (16 sites) and Underground Storage Tanks (139 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Toxics Release Inventory: TRI facilities report annual chemical releases to air, water, and land.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Check prevailing wind direction — downwind parcels face higher exposure than upwind or crosswind locations.
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Duncan
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the Duncan average
Your land is one point inside Duncan
Everything above resolves to Duncan as a whole — one PHZM band and one 28°F frost record, read across 27K acres. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at city scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better local average.
Your Lot vs the Duncan Average
Duncan Average
- ●USDA Zones 8a, averaged across Duncan
- ●One soil character for all of Duncan
- ●Frost dates read at Duncan's scale: Mar 13 to Nov 20
YOUR Parcel
- ✓Your exact zone, not Duncan's 8a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Duncan
Pull a site-specific report for your exact address in Duncan, Oklahoma — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Duncan averages can't show:
We read public map data around Duncan — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Duncan average
How we know this about Duncan
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Duncan’s own record; boundaries and acreage from US Census TIGER/Line 2025; the contamination records from the federal sources named in their beats above. Soil is not read at city grain anywhere on this page — there is no city-resolution survey in our data, which is why you will find no soil grid here rather than a statewide one wearing a local label. The resolution ledger below names every figure this page inherited.
Common questions about Duncan
When does frost risk typically end in Duncan?
The last hard freeze (28°F) in Duncan typically lands around Mar 13, 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 3.
When is the first frost in Duncan?
The first hard freeze (28°F) in Duncan typically arrives around Nov 20, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Nov 6, so the watching starts about Oct 21 — about 252 days after the spring freeze cleared.
How long is the growing season in Duncan?
Measured between 28°F hard freezes, Duncan sees about 252 frost-free days — roughly Mar 13 through Nov 20, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 3 to Nov 6, about 217 days.
Is the soil safe to grow vegetables in Duncan?
The federal record around Duncan is a meaningful one — 186 documented sites, mostly Underground Storage Tanks entries (139), the nearest Underground Storage Tanks record about 0.2 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.
How do I protect my plants from frost in Duncan?
From about Oct 21 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 20 (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 20. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Duncan's scale — its 8a band and its 252-day season. Your yard writes its own version of Duncan's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
What this page reads at Duncan’s own scale
6 of the readings below were taken at Duncan's own scale — its own ~252-day season between 28°F freezes, the 27,482 acres it covers and 186 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Duncan's own USDA hardiness band, zones 8aUSDA PHZM 2023
- Duncan's own 28°F hard-freeze dates, about Mar 13 and Nov 20 and the ~252-day span between themNOAA 1991–2020 Climate Normals
- 186 documented contamination sites on the federal record near Duncan, the closest Underground Storage Tanks record about 0.2 miles out from the town centreFederal environmental registers
- Duncan's boundary and the 27,482 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 8a and a ~252-day seasonGrowable Ground crop-matching engine
- The ecoregion at Duncan's own centroid, the Cross TimbersUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Duncan's 27,482 acres read through its county's SSURGO summaryfrom Stephens County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Stephens County
- The growing challenges every Oklahoma grower plans around — written at state scale, so they stay on the state guidefrom Oklahoma
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Stephens County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Duncan's 27,482 acreswhy one lot differs from the next →
- Which side of Duncan you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 27,482 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.2 miles out, measured from the town centrehow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — measured at your address, and averaged away by any Duncan-wide figureread your own land →
More in Oklahoma
Wider growing context
What grows across OklahomaDuncan sits outside our named growing regions, so Oklahoma as a whole is its closest context here.
Nearby growing guides