Denver, Colorado, sits in USDA hardiness zone 6a — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
A short list that earns its place here — cabbage, hazelnut, lavender, and collard greens — with any one site's soil, sun, and drainage making the final cut.
Even in Denver, 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 Denver 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 Denver — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Denver — the short answer
Denver, Colorado: USDA zone 6a, about 183 days between hard freezes, across 98K acres of city.
- USDA zone
- 6a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 20
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Oct 20
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~183
- NOAA 1991–2020 Climate Normals, 28°F — this town
- City area
- 98K 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 6a is Denver's average, not your lot's — a low corner or a tree line moves it. Against Denver's 183-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Denver
Each reading below is measured for Denver itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredDenver runs about 183 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
MeasuredDenver sits in USDA hardiness zone 6a.
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 Denver is in
Denver sits in the High Plains — EPA Level III, inside the wider Great Plains. That is read at Denver's own centroid rather than borrowed from Denver County.
What Grows in Denver
Every plant below cleared Denver's own zone 6a and its 183-day season. Each card opens that plant's Colorado profile. How we score.
Is it too late to plant in Denver?
Too late for some crops, right on time for others — a growing season is a sequence, not a deadline. Cool-season crops can go in from around Mar 23; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 20 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 20 — long-season crops need about 90 days of runway, quick greens only 30. As the window narrows, the plantings just get faster — fall brassicas, then greens, then garlic to finish.
What's on the federal record near Denver
Closest first, within ~10 miles of Denver. Listing isn't leaking, and distance isn't exposure.
- CCOD Stapleton Int'l Airport Main BoilerUnderground Storage Tanks · 450 ft
- Continental AirlinesUnderground Storage Tanks · 0.6 mi
- Vehicle Maintenance CenterUnderground Storage Tanks · 0.6 mi
- Sam's Club #4777Underground Storage Tanks · 0.6 mi
- MaintenanceUnderground Storage Tanks · 0.6 mi
- FAA Stapleton Dend RtrUnderground Storage Tanks · 0.6 mi
- FAA Rrv Glide SlopeUnderground Storage Tanks · 0.6 mi
- FAA Denver Rrv Alsf IiUnderground Storage Tanks · 0.6 mi
- Delta Air LinesUnderground Storage Tanks · 0.6 mi
- CCOD Vault B Stapleton AirportUnderground Storage Tanks · 0.6 mi
- Spo LocUnderground Storage Tanks · 0.6 mi
- FAA Stapleton Denb RtrUnderground Storage Tanks · 0.6 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Denver'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 Denver.
Sources Checked
within ~10 miles of Denver
Severity Distribution
within ~10 miles of Denver
Highest-Severity Sites
Know Before You Grow
- •Underground tanks leak petroleum as they age — near a former filling station, test the soil.
- •Near a brownfield, raised beds of imported soil give your food clean ground.
- •On a private well, test for nitrates: above 10 mg/L the water needs treatment before irrigating.
Check your specific parcel in Denver
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 Denver average
Your land is one point inside Denver
Everything above resolves to Denver as a whole — one PHZM band and one 28°F frost record, read across 98K 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 city 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 Denver Average
Denver Average
- ●USDA Zones 6a, averaged across Denver
- ●One soil character for all of Denver
- ●Frost dates read at Denver's scale: Apr 20 to Oct 20
YOUR Parcel
- ✓Your exact zone, not Denver's 6a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Denver
Pull a site-specific report for your exact address in Denver, Colorado — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Denver averages can't show:
We read public map data around Denver — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Denver average
How we know this about Denver
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at this city’s own centroid; hard-freeze dates from NOAA 1991–2020 28°F normals at Denver’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 city grain anywhere on this page — there is no city-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 Denver
When does frost risk typically end in Denver?
The last hard freeze (28°F) in Denver typically lands around Apr 20, 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 11.
When is the first frost in Denver?
The first hard freeze (28°F) in Denver typically arrives around Oct 20, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Oct 6, so the watching starts about Sep 20 — about 183 days after the spring freeze cleared.
How long is the growing season in Denver?
Measured between 28°F hard freezes, Denver sees about 183 frost-free days — roughly Apr 20 through Oct 20, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer May 11 to Oct 6, about 148 days.
Is the soil safe to grow vegetables in Denver?
The federal record around Denver runs heavier than most — 4,991 documented sites, mostly Underground Storage Tanks entries (2,742), the nearest Underground Storage Tanks record under a tenth of a mile out — so test the soil before planting food in the ground, and raised beds with clean imported soil grow well in the meantime. Even here, proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what's recorded and where.
How do I protect my plants from frost in Denver?
From about Sep 20 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 20 (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 20. Hardy greens and roots shrug off light frost and sweeten after it — leave them in.
Everything above is measured at Denver's scale — its 6a band and its 183-day season. Your yard writes its own version of Denver'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 Denver’s own scale
6 of the readings below were taken at Denver's own scale — its own ~183-day season between 28°F freezes, the 97,967 acres it covers and 4,991 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Denver's own USDA hardiness band, zones 6aUSDA PHZM 2023
- Denver's own 28°F hard-freeze dates, about Apr 20 and Oct 20 and the ~183-day span between themNOAA 1991–2020 Climate Normals
- 4,991 documented contamination sites on the federal record near Denver, the closest Underground Storage Tanks record under a tenth of a mile out from the town centreFederal environmental registers
- Denver's boundary and the 97,967 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 6a and a ~183-day seasonGrowable Ground crop-matching engine
- The ecoregion at Denver's own centroid, the High PlainsUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Denver's 97,967 acres read through its county's SSURGO summaryfrom Denver County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Denver County
- The growing challenges every Colorado grower plans around — written at state scale, so they stay on the state guidefrom Colorado
- Butterfly and beetle records, and the farmland pesticide estimate — all published county-widefrom Denver County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Denver's 97,967 acreswhy one lot differs from the next →
- Which side of Denver you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 97,967 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record under a tenth of a mile 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 Denver-wide figureread your own land →