Boulder Flats, Wyoming, sits in USDA hardiness zone 5a — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
The conditions favor cabbage, cranberry, lavender, and collard greens, among others — though every individual site edits that list with its own soil, sun, and drainage.
Even in Boulder Flats, 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 Boulder Flats 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 Boulder Flats — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Boulder Flats — the short answer
Boulder Flats, Wyoming: USDA zone 5a, about 149 days between hard freezes, across 12K acres of town.
- USDA zone
- 5a
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 7
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 3
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~149
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 12K 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 5a is Boulder Flats's average, not your lot's — a low corner or a tree line moves it. Against Boulder Flats's 149-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Boulder Flats
Each reading below is measured for Boulder Flats itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredBoulder Flats runs about 149 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
MeasuredBoulder Flats 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 Boulder Flats is in
Boulder Flats sits in the Wyoming Basin — EPA Level III, inside the wider North American Deserts. That is read at Boulder Flats's own centroid rather than borrowed from Fremont County.
What Grows in Boulder Flats
Every plant below cleared Boulder Flats's own zone 5a and its 149-day season. Each card opens that plant's Wyoming profile. How we score.
Is it too late to plant in Boulder Flats?
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 9; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 7 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 3 — long-season crops need about 90 days of runway, quick greens only 30. When the window is tight, the fall moves are quick ones — baby greens, radishes, and garlic set for next season.
What's on the federal record near Boulder Flats
Closest first, within ~10 miles of Boulder Flats. Listing isn't leaking, and distance isn't exposure.
- 1S-01E-31dda01Nitrate · 0.9 mi
- 34-100-35bca01Nitrate · 2.7 mi
- Washakie County ShopUnderground Storage Tanks · 3.0 mi
- 34-099-30dbc01Nitrate · 3.8 mi
- 1S-01E-22bcb01Nitrate · 4.0 mi
- 34-099-31aab01Nitrate · 4.3 mi
- 1S-01E-15ccc01Nitrate · 4.3 mi
- 1S-01E-22bba01Nitrate · 4.3 mi
- PLUNKETT OIL FIELDSuperfund · 4.7 mi
- Wyoming Indian Elementary SchoolUnderground Storage Tanks · 4.7 mi
- Jimmie D. FreemanUnderground Storage Tanks · 4.9 mi
- 33-099-06aaa02Nitrate · 5.0 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Boulder Flats'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 Boulder Flats.
Total Sites
164
within ~10 miles of Boulder Flats
Risk Level
Elevated
Highest-severity
2 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Boulder Flats
Severity Distribution
within ~10 miles of Boulder Flats
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Boulder Flats, Nitrate runs higher than the national average — 70 sites within ~10 miles of Boulder Flats. 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.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Boulder Flats
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 Boulder Flats average
Your land is one point inside Boulder Flats
Everything above resolves to Boulder Flats as a whole — one PHZM band and one 28°F frost record, read across 12K 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 town 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 Boulder Flats Average
Boulder Flats Average
- ●USDA Zones 5a, averaged across Boulder Flats
- ●One soil character for all of Boulder Flats
- ●Frost dates read at Boulder Flats's scale: May 7 to Oct 3
YOUR Parcel
- ✓Your exact zone, not Boulder Flats's 5a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Boulder Flats
Pull a site-specific report for your exact address in Boulder Flats, Wyoming — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Boulder Flats averages can't show:
We read public map data around Boulder Flats — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Boulder Flats average
How we know this about Boulder Flats
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this town’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Boulder Flats’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 town grain anywhere on this page — there is no town-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 Boulder Flats
When does frost risk typically end in Boulder Flats?
The last hard freeze (28°F) in Boulder Flats typically lands around May 7, 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 May 28.
When is the first frost in Boulder Flats?
The first hard freeze (28°F) in Boulder Flats typically arrives around Oct 3, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Sep 19, so the watching starts about Sep 3 — about 149 days after the spring freeze cleared.
How long is the growing season in Boulder Flats?
Measured between 28°F hard freezes, Boulder Flats sees about 149 frost-free days — roughly May 7 through Oct 3, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 28 to Sep 19, about 114 days.
Is the soil safe to grow vegetables in Boulder Flats?
The federal record around Boulder Flats is a meaningful one — 164 documented sites, mostly Nitrate entries (70), the nearest Nitrate record about 0.9 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 Boulder Flats?
With about 149 frost-free days between hard freezes, Boulder Flats 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 177 to 205 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 7 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Boulder Flats's scale — its 5a band and its 149-day season. Your yard writes its own version of Boulder Flats'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 Boulder Flats’s own scale
6 of the readings below were taken at Boulder Flats's own scale — its own ~149-day season between 28°F freezes, the 11,636 acres it covers and 164 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Boulder Flats's own USDA hardiness band, zones 5aUSDA PHZM 2023
- Boulder Flats's own 28°F hard-freeze dates, about May 7 and Oct 3 and the ~149-day span between themNOAA 1991–2020 Climate Normals
- 164 documented contamination sites on the federal record near Boulder Flats, the closest Nitrate record about 0.9 miles out from the town centreFederal environmental registers
- Boulder Flats's boundary and the 11,636 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5a and a ~149-day seasonGrowable Ground crop-matching engine
- The ecoregion at Boulder Flats's own centroid, the Wyoming BasinUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Boulder Flats's 11,636 acres read through its county's SSURGO summaryfrom Fremont County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Fremont County
- The growing challenges every Wyoming grower plans around — written at state scale, so they stay on the state guidefrom Wyoming
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Fremont County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Boulder Flats's 11,636 acreswhy one lot differs from the next →
- Which side of Boulder Flats you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 11,636 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Nitrate record about 0.9 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 Boulder Flats-wide figureread your own land →
More in Wyoming
Wider growing context
What grows across WyomingBoulder Flats sits outside our named growing regions, so Wyoming as a whole is its closest context here.
Nearby growing guides