San Juan County, in Colorado, sits in USDA hardiness zone 4b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Well-matched crops include zucchini, cranberry, cilantro, and okra, and the gap between "grows in the area" and "grows in your yard" is closed by soil, sun, and drainage.
San Juan 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
San Juan County holds more than one microclimate.
Soils and elevations shift across San Juan 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 San Juan County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
San Juan County — the short answer
San Juan County, Colorado: USDA zone 4b, about 98 days between hard freezes, across 248K acres.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jun 10
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Sep 16
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~98
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 248K 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 San Juan County's average, not your lot's — a low corner or a tree line moves it. Against San Juan County's 98-day season, see what your own ground reads.
Heat in San Juan County
Across a year, San Juan County accumulates about 270 growing degree days above 50°F, about 1,562 fewer than the middle Colorado county — ahead of 5 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 San Juan County
Across San Juan County, the ground is predominantly Mollisols, where Needleton, Frisco, and Fughes are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 6.1–7.0, slightly acidic. Rainfall drains through hydrologic group C soils.
Soil order
Mollisols
Drainage
Well drained
Hydric soils
1%
Soil still varies lot by lot — soil types explained.
How the ground varies across San Juan County
The USDA soil survey maps 87% of San Juan County as well drained — but another 5% drains differently: 3% excessively drained, 1% poorly drained.
Needleton is the most extensive named soil at 5% of mapped acres, then Frisco (4%) and Fughes (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 San Juan County
Each reading below is measured for San Juan 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 San Juan 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 San Juan County runs about pH 6.1–7.0, 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
MeasuredSan Juan County runs about 98 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
MeasuredSan Juan 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 San Juan County is in
San Juan County sits in the Southern Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. One consistent ecological setting across the whole county.
What Grows in San Juan County
We scored all 1,086 plants against San Juan County's own USDA zone 4b and its own 98-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 San Juan County?
Usually not — gardeners here simply switch what goes in the ground as the season moves. Cool-season crops can go in from around May 13; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jun 10 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 16 — 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.
Safe to Grow Here?
What the federal record shows across San Juan County — and how to grow with it.
We checked the federal record across San Juan County — 558 documented sites across 4 of the 9 source types we track.
The most significant on record: 10 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
San Juan County carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds with clean imported soil grow well almost anywhere in the meantime.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near San Juan County
Closest first, across San Juan County. Listing isn't leaking, and distance isn't exposure.
- King GroupMining · 500 ft
- KingMining · 500 ft
- Thunder TunnelMining · 1800 ft
- Mystery Gold GroupMining · 0.5 mi
- Alethea GroupMining · 0.6 mi
- Mystery Group, FairviewMining · 0.6 mi
- MarcellaMining · 0.6 mi
- Mighty Monarch Et AlMining · 0.8 mi
- North StarMining · 0.8 mi
- DoraMining · 0.8 mi
- Champion MineMining · 0.9 mi
- Clara MineMining · 0.9 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from San Juan 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 San Juan County.
Sources Checked
across San Juan County
Severity Distribution
across San Juan County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around San Juan County, two things run higher than the national average across San Juan County — Mining (534 sites) and Superfund (10 sites). Knowing it is half the work — and it's nothing a thoughtful grower can't plan for.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Superfund: Superfund sites represent the most severe contamination in the federal system.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Commission professional soil testing before any food production (test for heavy metals, VOCs, and SVOCs).
Check your specific parcel in San Juan 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 San Juan County average
Your land is one point inside San Juan County
Everything above resolves to San Juan County as a whole — one PHZM band and one county frost record, read across 248K 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 San Juan County Average
San Juan County Average
- ●USDA Zones 4b, averaged across San Juan County
- ●One soil character for all of San Juan County
- ●Frost dates read at San Juan County's scale: Jun 10 to Sep 16
YOUR Parcel
- ✓Your exact zone, not San Juan County's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in San Juan County
Pull a site-specific report for your exact address in San Juan County, Colorado — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that San Juan County averages can't show:
We read public map data around San Juan County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the San Juan County average
How we know this about San Juan 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 San Juan County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about San Juan County
When does frost risk typically end in San Juan County?
The last hard freeze (28°F) in San Juan County typically lands around Jun 10, 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 1.
How long is the growing season in San Juan County?
Measured between 28°F hard freezes, San Juan County sees about 98 frost-free days — roughly Jun 10 through Sep 16, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jul 1 to Sep 2, about 63 days.
Is the soil safe to grow vegetables in San Juan County?
The federal record around San Juan County runs heavier than most — 558 documented sites, mostly Mining entries (534), the nearest Mining 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 gardeners stretch the season in San Juan County?
With about 98 frost-free days between hard freezes, San Juan 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 126 to 154 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the Jun 10 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at San Juan County's scale — its 4b band and its 98-day season. Your yard writes its own version of San Juan 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 San Juan County’s own scale
7 of the readings below were taken at San Juan County's own scale — its own ~98-day span between 28°F freezes, the 3 most extensive soil series mapped here and 558 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- San Juan County's own USDA hardiness band, zones 4bUSDA PHZM 2023
- San Juan County's own 28°F hard-freeze dates and its ~98-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in San Juan CountyUSDA NRCS SSURGO
- 558 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record under a tenth of a mile outFederal environmental registers
- San Juan County's boundary and the 248,010 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~98-day seasonGrowable Ground crop-matching engine
- San Juan County sitting wholly inside the Southern RockiesUS EPA Level III Ecoregions
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 San Juan County — the ~98 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 San Juan County's 248,010 acreswhy one lot differs from the next →
- Which of those 558 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 San Juan Countyread your own land →