Boulder, Utah, sits in USDA hardiness zone 6b — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
Among the crops suited to this profile: cabbage, blackberry, california poppy, and collard greens. The site-level story — soil, sun, drainage — decides the rest.
Even in Boulder, 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 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 — soil, climate, flood, and parcel records. How we handle your address.
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Boulder — the short answer
Boulder, Utah: USDA zone 6b, about 187 days between hard freezes, across 13K acres of town.
- USDA zone
- 6b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 24
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 28
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~187
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 13K 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 6b is Boulder's average, not your lot's — a low corner or a tree line moves it. Against Boulder's 187-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Boulder
Each reading below is measured for Boulder itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredBoulder runs about 187 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredBoulder sits in USDA hardiness zone 6b.
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 is in
Boulder sits in the Colorado Plateaus — EPA Level III, inside the wider North American Deserts. That is read at Boulder's own centroid rather than borrowed from Garfield County.
What Grows in Boulder
Every plant below cleared Boulder's own zone 6b and its 187-day season. Each card opens that plant's Utah profile. How we score.
Is it too late to plant in Boulder?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around Mar 27; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 24 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 28 — long-season crops need about 90 days of runway, quick greens only 30. The tail of the season still works: sixty-day crops into late summer, quick greens after, garlic last of all.
What's on the federal record near Boulder
Closest first, within ~10 miles of Boulder. Listing isn't leaking, and distance isn't exposure.
- HALL'S STOREUnderground Storage Tanks · 1.1 mi
- DOYLE MOOSMANUnderground Storage Tanks · 1.1 mi
- BURR TRAIL CAFEUnderground Storage Tanks · 1.5 mi
- HILLS AND HOLLOWS SERVICEUnderground Storage Tanks · 1.7 mi
- (D-32- 4)35bac- 1Nitrate · 4.2 mi
- HorseheadMining · 9.3 mi
Measured from Boulder'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.
Sources Checked
within ~10 miles of Boulder
Severity Distribution
within ~10 miles of Boulder
Highest-Severity Sites
Know Before You Grow
- •Underground tanks leak petroleum as they age — near a former filling station, test the soil.
- •On a private well, test for nitrates: above 10 mg/L the water needs treatment before irrigating.
- •Mine waste leaches heavy metals. Test for lead, arsenic and cadmium before growing food here.
Check your specific parcel in Boulder
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 average
Your land is one point inside Boulder
Everything above resolves to Boulder as a whole — one PHZM band and one 28°F frost record, read across 13K 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 Average
Boulder Average
- ●USDA Zones 6b, averaged across Boulder
- ●One soil character for all of Boulder
- ●Frost dates read at Boulder's scale: Apr 24 to Oct 28
YOUR Parcel
- ✓Your exact zone, not Boulder's 6b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Boulder
Pull a site-specific report for your exact address in Boulder, Utah — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Boulder averages can't show:
We read public map data around Boulder — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Boulder average
How we know this about Boulder
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’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
When does frost risk typically end in Boulder?
The last hard freeze (28°F) in Boulder typically lands around Apr 24, 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 15.
When is the first frost in Boulder?
The first hard freeze (28°F) in Boulder typically arrives around Oct 28, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 14, so the watching starts about Sep 28 — about 187 days after the spring freeze cleared.
How long is the growing season in Boulder?
Measured between 28°F hard freezes, Boulder sees about 187 frost-free days — roughly Apr 24 through Oct 28, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 15 to Oct 14, about 152 days.
Is the soil safe to grow vegetables in Boulder?
The federal record around Boulder is light — 7 documented sites across the 9 federal source types we checked, mostly Underground Storage Tanks entries (4), the nearest Underground Storage Tanks record about 1.1 miles out — and proximity to a documented site is information, not a diagnosis of any one yard. Growing food here starts from a strong position; a soil test before new food beds settles any site-specific question.
How do I protect my plants from frost in Boulder?
From about Sep 28 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 Oct 28 (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 Oct 28. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Boulder's scale — its 6b band and its 187-day season. Your yard writes its own version of Boulder'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’s own scale
6 of the readings below were taken at Boulder's own scale — its own ~187-day season between 28°F freezes, the 13,405 acres it covers and 7 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Boulder's own USDA hardiness band, zones 6bUSDA PHZM 2023
- Boulder's own 28°F hard-freeze dates, about Apr 24 and Oct 28 and the ~187-day span between themNOAA 1991–2020 Climate Normals
- 7 documented contamination sites on the federal record near Boulder, the closest Underground Storage Tanks record about 1.1 miles out from the town centreFederal environmental registers
- Boulder's boundary and the 13,405 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6b and a ~187-day seasonGrowable Ground crop-matching engine
- The ecoregion at Boulder's own centroid, the Colorado PlateausUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Boulder's 13,405 acres read through its county's SSURGO summaryfrom Garfield County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Garfield County
- The growing challenges every Utah grower plans around — written at state scale, so they stay on the state guidefrom Utah
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Garfield County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Boulder's 13,405 acreswhy one lot differs from the next →
- Which side of Boulder you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 13,405 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 1.1 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-wide figureread your own land →
More in Utah
Wider growing context
What grows across UtahBoulder sits outside our named growing regions, so Utah as a whole is its closest context here.