Harmon County, in Oklahoma, sits in USDA hardiness zone 7b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
These conditions suit cabbage, prickly pear, california poppy, and collard greens — a starting list any specific site will trim or extend with its own soil, sun, and drainage.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Harmon County holds more than one microclimate.
Soils and elevations shift across Harmon County, so your frost dates and drainage aren't the county average. 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 Harmon County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Harmon County — the short answer
Harmon County, Oklahoma: USDA zone 7b, about 235 days between hard freezes, across 344K acres.
- USDA zone
- 7b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Mar 22
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Nov 12
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~235
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 344K acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 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 7b is Harmon County's average, not your lot's — a low corner or a tree line moves it. Against Harmon County's 235-day season, see what your own ground reads.
Heat and winter chill in Harmon County
Across a year, Harmon County accumulates about 5,018 growing degree days above 50°F, about 298 more than the middle Oklahoma county — ahead of 63 of Oklahoma’s 77 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Winter banks about 1,820 hours below 45°F, 99 fewer than the Oklahoma middle of 1,919. Chill is what tells a fruit tree its dormancy is over, and it is set by climate rather than by anything you can build.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Harmon County
Across Harmon County, the ground is predominantly Inceptisols, where Westill, Woodward, and Grandfield are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 7.0–7.9, slightly alkaline. Rainfall drains through hydrologic group D soils.
Soil order
Inceptisols
Drainage
Well drained
Prime farmland
38%
Hydric soils
0%
Soil still varies lot by lot — soil types explained.
How the ground varies across Harmon County
The USDA soil survey maps 94% of Harmon County as well drained — but another 5% drains differently: 2% excessively drained, 1% somewhat poorly drained.
Westill is the most extensive named soil at 9% of mapped acres, then Woodward (8%) and Grandfield (7%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Harmon County
Each reading below is measured for Harmon County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Harmon County are well drained, in hydrologic group D — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Harmon County runs about pH 7.0–7.9, on the alkaline side.
Many vegetables cope, but acid-lovers like blueberries struggle, and iron and manganese lock up above about pH 7.5 — leaves yellow between the veins even in rich soil.
Elemental sulfur and generous organic matter lower pH slowly for the beds that need it; test first so you add only what the soil actually calls for.
USDA NRCS SSURGO
Season length
MeasuredHarmon County runs about 235 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
MeasuredHarmon County sits in USDA hardiness zone 7b.
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 Harmon County is in
Harmon County spans 2 EPA Level III ecoregions — Central Great Plains (75%) and Southwestern Tablelands (25%). Which one your land falls in changes what grows wild there and how the ground behaves, and a county-wide answer cannot tell you which.
What Grows in Harmon County
We scored all 1,086 plants against Harmon County's own USDA zone 7b and its own 235-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's Oklahoma profile.
Is it too late to plant in Harmon County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Feb 22; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Mar 22 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Nov 12 — 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 gets applied to farmland in Harmon County
USGS estimates 99,445 lb of Glyphosate on Harmon County farmland in 2019, its largest by weight, ahead of 2,4-d (46,956 lb) and Acetochlor (45,790 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Harmon County — and how to grow with it.
We checked the federal record across Harmon County — 50 documented sites across 3 of the 9 source types we track.
The most significant on record: 1 mining site (prospects, none worked). Historic and active mines that may leach heavy metals like arsenic, lead, and cadmium.
The federal record across Harmon County is a modest one — a typical footprint for a growing area. Nothing here calls for alarm; it's worth knowing which recorded sites sit closest to where you grow, and each one on the map carries its type and location. If one turns out to be a near neighbor, a one-time soil test settles the question.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Harmon County
Closest first, across Harmon County. Listing isn't leaking, and distance isn't exposure.
- Hollis StationUnderground Storage Tanks · 4.1 mi
- Mcknight Gro & Sta.Underground Storage Tanks · 4.1 mi
- Hollis Municipal AirportUnderground Storage Tanks · 4.7 mi
- Jackson Aerial Spraying Inc.Underground Storage Tanks · 5.2 mi
- Okla Dept Of TransUnderground Storage Tanks · 5.3 mi
- National Guard ArmoryUnderground Storage Tanks · 5.3 mi
- Lee Roy CrawfordUnderground Storage Tanks · 5.4 mi
- The Water'n HoleUnderground Storage Tanks · 5.5 mi
- Fina StationUnderground Storage Tanks · 5.5 mi
- Shamrock StationUnderground Storage Tanks · 5.5 mi
- Love's Country Store #10Underground Storage Tanks · 5.9 mi
- Phillips 66 Co #019053Underground Storage Tanks · 6.0 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Harmon County'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 Harmon County.
Total Sites
50
across Harmon County
Risk Level
Moderate
Highest-severity
1 mining site (prospects, none worked)
Severity Distribution
across Harmon County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Harmon County, two things run higher than the national average across Harmon County — Nitrate (18 sites) and Underground Storage Tanks (31 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Harmon County
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 Harmon County average
Your land is one point inside Harmon County
Everything above resolves to Harmon County as a whole — one PHZM band and one county frost record, read across 344K 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 county 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 county average.
Your Lot vs the Harmon County Average
Harmon County Average
- ●USDA Zones 7b, averaged across Harmon County
- ●One soil character for all of Harmon County
- ●Frost dates read at Harmon County's scale: Mar 22 to Nov 12
YOUR Parcel
- ✓Your exact zone, not Harmon County's 7b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Harmon County
Pull a site-specific report for your exact address in Harmon County, Oklahoma — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Harmon County averages can't show:
We read public map data around Harmon County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Harmon County average
How we know this about Harmon County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Harmon County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Harmon County
When does frost risk typically end in Harmon County?
The last hard freeze (28°F) in Harmon County typically lands around Mar 22, 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 12.
How long is the growing season in Harmon County?
Measured between 28°F hard freezes, Harmon County sees about 235 frost-free days — roughly Mar 22 through Nov 12, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 12 to Oct 29, about 200 days.
Is the soil safe to grow vegetables in Harmon County?
The federal record around Harmon County shows 50 documented sites, mostly Underground Storage Tanks entries (31), the nearest Underground Storage Tanks record about 4.1 miles out — a typical footprint for a growing area, and proximity to a documented site is information, not a diagnosis of any one yard. It's worth seeing which recorded sites sit closest to where you grow, and testing the soil before new food beds near any of them.
Everything above is measured at Harmon County's scale — its 7b band and its 235-day season. Your yard writes its own version of Harmon County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads Oklahoma's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Harmon County’s own scale
8 of the readings below were taken at Harmon County's own scale — its own ~235-day span between 28°F freezes, the 3 most extensive soil series mapped here and 50 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Harmon County's own USDA hardiness band, zones 7bUSDA PHZM 2023
- Harmon County's own 28°F hard-freeze dates and its ~235-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Harmon CountyUSDA NRCS SSURGO
- 50 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Underground Storage Tanks record about 4.1 miles outFederal environmental registers
- Harmon County's boundary and the 343,845 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 7b and a ~235-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Harmon County spans, Central Great Plains the largestUS EPA Level III Ecoregions
- Which agricultural compounds go onto Harmon County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Oklahoma grower plans around — written at state scale, so they stay on the state guidefrom Oklahoma
What this page can’t tell you
- How the season shifts across Harmon County — the ~235 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Harmon County's 343,845 acreswhy one lot differs from the next →
- Which of those 50 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Harmon Countyread your own land →