St. Mary's, Colorado, sits in USDA hardiness zone 5b — enough range to grow cool-season vegetables, hardy fruit, and warm-season crops that mature before the first hard frost.
Expect pumpkin, blackberry, lavender, and zucchini to be strong candidates here; the deciding factors on any one parcel stay local — soil, sun, and drainage.
Even in St. Mary's, 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 St. Mary's 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 St. Mary's — soil, climate, flood, and parcel records. How we handle your address.
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St. Mary's — the short answer
St. Mary's, Colorado: USDA zone 5b, about 88 days between hard freezes, across 920 acres of town.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jun 13
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Sep 9
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~88
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 920 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 5b is St. Mary's's average, not your lot's — a low corner or a tree line moves it. Against St. Mary's's 88-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in St. Mary's
Each reading below is measured for St. Mary's itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredSt. Mary's runs about 88 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
MeasuredSt. Mary's sits in USDA hardiness zone 5b.
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 St. Mary's is in
St. Mary's sits in the Southern Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at St. Mary's's own centroid rather than borrowed from Clear Creek County.
What Grows in St. Mary's
Every plant below cleared St. Mary's's own zone 5b and its 88-day season. Each card opens that plant's Colorado profile. How we score.
Is it too late to plant in St. Mary's?
Almost never — the real question is what to plant next. Cool-season crops can go in from around May 16; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jun 13 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 9 — long-season crops need about 90 days of runway, quick greens only 30. In a season this compact, fast finishers and cold-hardy greens do the late work, and garlic tucked in before the freeze repays you next summer.
What's on the federal record near St. Mary's
Closest first, within ~10 miles of St. Mary's. Listing isn't leaking, and distance isn't exposure.
- Federal Aviation AdministrationUnderground Storage Tanks · 850 ft
- HarlemMining · 1200 ft
- Old Stone WallMining · 1200 ft
- Nettie B.Mining · 1200 ft
- Miss DividendsMining · 1200 ft
- ClaraMining · 1400 ft
- Floyd J Viele PropertyUnderground Storage Tanks · 2400 ft
- Alice Mine-Glory Hole.Mining · 2400 ft
- PuritanMining · 0.9 mi
- Lombard MineMining · 1.2 mi
- Seeman TunnelMining · 2.2 mi
- Last ChanceMining · 2.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from St. Mary's'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 St. Mary's.
Sources Checked
within ~10 miles of St. Mary's
Severity Distribution
within ~10 miles of St. Mary's
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around St. Mary's, Mining runs higher than the national average — 671 sites within ~10 miles of St. Mary's. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around 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.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Check your specific parcel in St. Mary's
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 St. Mary's average
Your land is one point inside St. Mary's
Everything above resolves to St. Mary's as a whole — one PHZM band and one 28°F frost record, read across 920 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 St. Mary's Average
St. Mary's Average
- ●USDA Zones 5b, averaged across St. Mary's
- ●One soil character for all of St. Mary's
- ●Frost dates read at St. Mary's's scale: Jun 13 to Sep 9
YOUR Parcel
- ✓Your exact zone, not St. Mary's's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in St. Mary's
Pull a site-specific report for your exact address in St. Mary's, Colorado — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that St. Mary's averages can't show:
We read public map data around St. Mary's — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the St. Mary's average
How we know this about St. Mary's
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 St. Mary's’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 St. Mary's
When does frost risk typically end in St. Mary's?
The last hard freeze (28°F) in St. Mary's typically lands around Jun 13, 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 Jul 4.
When is the first frost in St. Mary's?
The first hard freeze (28°F) in St. Mary's typically arrives around Sep 9, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Aug 26, so the watching starts about Aug 10 — about 88 days after the spring freeze cleared.
How long is the growing season in St. Mary's?
Measured between 28°F hard freezes, St. Mary's sees about 88 frost-free days — roughly Jun 13 through Sep 9, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jul 4 to Aug 26, about 53 days.
Is the soil safe to grow vegetables in St. Mary's?
The federal record around St. Mary's runs heavier than most — 796 documented sites, mostly Mining entries (671), the nearest Underground Storage Tanks record about 0.2 miles 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 gardeners stretch the season in St. Mary's?
With about 88 frost-free days between hard freezes, St. Mary's 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 116 to 144 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the Jun 13 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at St. Mary's's scale — its 5b band and its 88-day season. Your yard writes its own version of St. Mary's'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 St. Mary's’s own scale
6 of the readings below were taken at St. Mary's's own scale — its own ~88-day season between 28°F freezes, the 920 acres it covers and 796 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- St. Mary's's own USDA hardiness band, zones 5bUSDA PHZM 2023
- St. Mary's's own 28°F hard-freeze dates, about Jun 13 and Sep 9 and the ~88-day span between themNOAA 1991–2020 Climate Normals
- 796 documented contamination sites on the federal record near St. Mary's, the closest Underground Storage Tanks record about 0.2 miles out from the town centreFederal environmental registers
- St. Mary's's boundary and the 920 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~88-day seasonGrowable Ground crop-matching engine
- The ecoregion at St. Mary's's own centroid, the Southern RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so St. Mary's's 920 acres read through its county's SSURGO summaryfrom Clear Creek County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Clear Creek 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 Clear Creek County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among St. Mary's's 920 acreswhy one lot differs from the next →
- Which side of St. Mary's you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 920 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Underground Storage Tanks record about 0.2 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 St. Mary's-wide figureread your own land →