Routt County, in Colorado, sits in USDA hardiness zone 4b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Reliable performers under these conditions include cabbage, cranberry, cilantro, and collard greens; what your own ground favors still comes down to its soil, sun, and drainage.
Routt County lies within the Colorado High Country (Central Rockies) — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Routt County holds more than one microclimate.
Soils and elevations shift across Routt 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 Routt County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Routt County — the short answer
Routt County, Colorado: USDA zone 4b, about 135 days between hard freezes, across 1.5M acres.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 16
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Sep 28
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~135
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 1.5M 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 4b is Routt County's average, not your lot's — a low corner or a tree line moves it. Against Routt County's 135-day season, see what your own ground reads.
Heat in Routt County
Across a year, Routt County accumulates about 1,271 growing degree days above 50°F, about 561 fewer than the middle Colorado county — ahead of 24 of Colorado’s 64 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 Routt County
Across Routt County, the ground is predominantly Mollisols, where Leighcan, Lintim, and Foidel are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 6.0–7.0, slightly acidic. Rainfall drains through hydrologic group C soils.
Soil order
Mollisols
Drainage
Well drained
Hydric soils
5%
Soil still varies lot by lot — soil types explained.
How the ground varies across Routt County
The USDA soil survey maps 84% of Routt County as well drained — but another 12% drains differently: 6% somewhat excessively drained, 3% very poorly drained.
Leighcan is the most extensive named soil at 7% of mapped acres, then Lintim (6%) and Foidel (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 Routt County
Each reading below is measured for Routt 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 Routt 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 Routt County runs about pH 6.0–7.0, close to neutral.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Season length
MeasuredRoutt County runs about 135 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
MeasuredRoutt County sits in USDA hardiness zone 4b.
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 Routt County is in
Routt County spans 2 EPA Level III ecoregions — Southern Rockies (93%) and Wyoming Basin (7%). 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 Routt County
We scored all 1,086 plants against Routt County's own USDA zone 4b and its own 135-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 Colorado profile.
Is it too late to plant in Routt County?
Almost never — the real question is what to plant next. Cool-season crops can go in from around Apr 18; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 16 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 28 — long-season crops need about 90 days of runway, quick greens only 30. Even here the calendar’s edges hold value: thirty-day greens late in the window, then garlic and a rested bed for spring.
Documented around Routt County
- monarch butterfly3 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Routt County
USGS estimates 7,142 lb of Glyphosate on Routt County farmland in 2019, its largest by weight, ahead of Metolachlor-s (2,899 lb) and Metolachlor & Metolachlor-s (2,899 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 Routt County — and how to grow with it.
We checked the federal record across Routt County — 259 documented sites across 7 of the 9 source types we track.
The most significant on record: 4 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 Routt 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 Routt County
Closest first, across Routt County. Listing isn't leaking, and distance isn't exposure.
- LAFARGE STEAMBOAT READY MIXToxics Release Inventory · 0.6 mi
- Starlite RanchUnderground Storage Tanks · 1.2 mi
- Micheletti StoreUnderground Storage Tanks · 1.8 mi
- TWIN LANDFILL CORPBrownfields · 2.5 mi
- Farrow Repair ServiceUnderground Storage Tanks · 3.9 mi
- Sleeping Giant GravelUnderground Storage Tanks · 4.1 mi
- Sunset ClaimsMining · 4.9 mi
- SB068417ANitrate · 5.0 mi
- Steamboat Springs MaintenanceUnderground Storage Tanks · 5.5 mi
- B & K Distributing IncUnderground Storage Tanks · 5.5 mi
- The Fuel StopUnderground Storage Tanks · 6.7 mi
- WEST ACRES ASBESTOSSuperfund · 6.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Routt 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 Routt County.
Total Sites
259
across Routt County
Risk Level
Elevated
Highest-severity
4 Superfund sites (none NPL-listed)
Sources Checked
across Routt County
Severity Distribution
across Routt County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Routt County, two things run higher than the national average across Routt County — Mining (39 sites) and PFAS (3 sites). That's not a problem with your land — it's information about it.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
PFAS: PFAS (per- and polyfluoroalkyl substances) are called "forever chemicals" because they do not biodegrade.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Test irrigation water source — this is the primary pathway for PFAS to reach garden crops.
Check your specific parcel in Routt 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 Routt County average
Your land is one point inside Routt County
Everything above resolves to Routt County as a whole — one PHZM band and one county frost record, read across 1.5M 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 Routt County Average
Routt County Average
- ●USDA Zones 4b, averaged across Routt County
- ●One soil character for all of Routt County
- ●Frost dates read at Routt County's scale: May 16 to Sep 28
YOUR Parcel
- ✓Your exact zone, not Routt County's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Routt County
Pull a site-specific report for your exact address in Routt County, Colorado — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Routt County averages can't show:
We read public map data around Routt County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Routt County average
How we know this about Routt 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 Routt County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Routt County
When does frost risk typically end in Routt County?
The last hard freeze (28°F) in Routt County typically lands around May 16, 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 6.
How long is the growing season in Routt County?
Measured between 28°F hard freezes, Routt County sees about 135 frost-free days — roughly May 16 through Sep 28, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 6 to Sep 14, about 100 days.
Is the soil safe to grow vegetables in Routt County?
The federal record around Routt County is a meaningful one — 259 documented sites, mostly Underground Storage Tanks entries (113), the nearest Toxics Release Inventory record about 0.6 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 Routt County?
With about 135 frost-free days between hard freezes, Routt 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 163 to 191 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 16 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Routt County's scale — its 4b band and its 135-day season. Your yard writes its own version of Routt 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 Colorado's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Routt County’s own scale
9 of the readings below were taken at Routt County's own scale — its own ~135-day span between 28°F freezes, the 3 most extensive soil series mapped here and 259 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Routt County's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Routt County's own 28°F hard-freeze dates and its ~135-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Routt CountyUSDA NRCS SSURGO
- 259 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Toxics Release Inventory record about 0.6 miles outFederal environmental registers
- Routt County's boundary and the 1,511,691 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~135-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Routt County spans, Southern Rockies the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Routt County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Routt County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Colorado grower plans around — written at state scale, so they stay on the state guidefrom Colorado
What this page can’t tell you
- How the season shifts across Routt County — the ~135 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 Routt County's 1,511,691 acreswhy one lot differs from the next →
- Which of those 259 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 Routt Countyread your own land →