Carbon County, in Wyoming, sits in USDA hardiness zone 5a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Growers here do well with cabbage, cranberry, lavender, and collard greens — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Carbon County holds more than one microclimate.
Soils and elevations shift across Carbon 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 Carbon County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Carbon County — the short answer
Carbon County, Wyoming: USDA zone 5a, about 142 days between hard freezes, across 5.1M acres.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 12
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 1
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~142
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 5.1M 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 5a is Carbon County's average, not your lot's — a low corner or a tree line moves it. Against Carbon County's 142-day season, see what your own ground reads.
Heat in Carbon County
Across a year, Carbon County accumulates about 1,586 growing degree days above 50°F, about 288 fewer than the middle Wyoming county — ahead of 7 of Wyoming’s 23 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.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Carbon County
Across Carbon County, the ground is predominantly Aridisols, where Rock River, Seminoe, and McFadden are the most extensive named soil series. The soil is generally well drained with a sandy loam surface. Topsoil pH runs about 7.0–8.0, slightly alkaline. Rainfall drains through hydrologic group C soils.
Soil order
Aridisols
Drainage
Well drained
Hydric soils
3%
Soil still varies lot by lot — soil types explained.
How the ground varies across Carbon County
The USDA soil survey maps 92% of Carbon County as well drained — but another 6% drains differently: 2% somewhat poorly drained, 2% very poorly drained.
Rock River is the most extensive named soil at 4% of mapped acres, then Seminoe (4%) and McFadden (4%).
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 Carbon County
Each reading below is measured for Carbon 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 Carbon County are well drained, in hydrologic group C — 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 Carbon County runs about pH 7.0–8.0, 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
MeasuredCarbon County runs about 142 days between hard freezes — a short growing season.
Long-maturing crops like melons, sweet potatoes, and winter squash can run out of runway before the first hard freeze, ripening late or not at all.
Lead with fast-maturing varieties, and stretch the season on both ends with cold frames, low tunnels, or a greenhouse.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredCarbon County sits in USDA hardiness zone 5a.
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 Carbon County is in
Carbon County spans 2 EPA Level III ecoregions — Wyoming Basin (78%) and Southern Rockies (22%). 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 Carbon County
We scored all 1,086 plants against Carbon County's own USDA zone 5a and its own 142-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 Wyoming profile.
Is it too late to plant in Carbon County?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Apr 14; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 12 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 1 — long-season crops need about 90 days of runway, quick greens only 30. Short seasons reward decisiveness — quick-maturing varieties late, hardy greens under cover, and next year’s garlic in the ground before it closes.
Documented around Carbon County
- monarch butterfly2 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Carbon County
USGS estimates 3,946 lb of Triclopyr on Carbon County farmland in 2019, its largest by weight, ahead of Glyphosate (1,400 lb) and Chlorpyrifos (1,035 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 Carbon County — and how to grow with it.
We checked the federal record across Carbon County — 789 documented sites across 8 of the 9 source types we track.
The most significant on record: 5 Superfund sites (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
There's a meaningful federal record across Carbon County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Carbon County
Closest first, across Carbon County. Listing isn't leaking, and distance isn't exposure.
- 20-084-07bcc01Nitrate · 2.1 mi
- 20-085-21bcb01Nitrate · 2.5 mi
- 21-085-26dab02Nitrate · 4.1 mi
- 21-085-26dab01Nitrate · 4.1 mi
- 21-085-23ddd01Nitrate · 4.6 mi
- Sinclair VP Pump SiteUnderground Storage Tanks · 4.8 mi
- 20-086-25dcb01Nitrate · 5.2 mi
- Fort Steele EstatesUnderground Storage Tanks · 5.2 mi
- Ellis Self-Service GasUnderground Storage Tanks · 5.8 mi
- 21-084-35bda01Nitrate · 5.8 mi
- 21-084-26cb 01Nitrate · 6.1 mi
- 20-084-13bba01Nitrate · 6.8 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Carbon 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 Carbon County.
Total Sites
789
across Carbon County
Risk Level
Elevated
Highest-severity
5 Superfund sites (none NPL-listed)
Severity Distribution
across Carbon County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Carbon County, two things run higher than the national average across Carbon County — Nitrate (410 sites) and Mining (83 sites). That's not a problem with your land — it's information about it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in Carbon 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 Carbon County average
Your land is one point inside Carbon County
Everything above resolves to Carbon County as a whole — one PHZM band and one county frost record, read across 5.1M 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 Carbon County Average
Carbon County Average
- ●USDA Zones 5a, averaged across Carbon County
- ●One soil character for all of Carbon County
- ●Frost dates read at Carbon County's scale: May 12 to Oct 1
YOUR Parcel
- ✓Your exact zone, not Carbon County's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Carbon County
Pull a site-specific report for your exact address in Carbon County, Wyoming — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Carbon County averages can't show:
We read public map data around Carbon County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Carbon County average
How we know this about Carbon 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 Carbon County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Carbon County
When does frost risk typically end in Carbon County?
The last hard freeze (28°F) in Carbon County typically lands around May 12, 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 Jun 2.
How long is the growing season in Carbon County?
Measured between 28°F hard freezes, Carbon County sees about 142 frost-free days — roughly May 12 through Oct 1, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 2 to Sep 17, about 107 days.
Is the soil safe to grow vegetables in Carbon County?
The federal record around Carbon County is a meaningful one — 789 documented sites, mostly Nitrate entries (410), the nearest Nitrate record about 2.1 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 gardeners stretch the season in Carbon County?
With about 142 frost-free days between hard freezes, Carbon County rewards the classic extension moves: floating row cover buys roughly two to four extra weeks at each shoulder — on this season that is a working window nearer 170 to 198 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 12 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Carbon County's scale — its 5a band and its 142-day season. Your yard writes its own version of Carbon 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 Wyoming's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Carbon County’s own scale
9 of the readings below were taken at Carbon County's own scale — its own ~142-day span between 28°F freezes, the 3 most extensive soil series mapped here and 789 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Carbon County's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Carbon County's own 28°F hard-freeze dates and its ~142-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Carbon CountyUSDA NRCS SSURGO
- 789 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Nitrate record about 2.1 miles outFederal environmental registers
- Carbon County's boundary and the 5,054,553 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~142-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Carbon County spans, Wyoming Basin the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Carbon County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Carbon County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Wyoming grower plans around — written at state scale, so they stay on the state guidefrom Wyoming
What this page can’t tell you
- How the season shifts across Carbon County — the ~142 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 Carbon County's 5,054,553 acreswhy one lot differs from the next →
- Which of those 789 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 Carbon Countyread your own land →