Rio Grande County, in Colorado, sits in USDA hardiness zone 5b — a band that supports both cool-season staples and warm-season crops chosen to fit the local frost window.
Growers here do well with pumpkin, blackberry, lavender, and zucchini — with the usual caveat that any single yard's soil, sun, and drainage cast the deciding vote.
Rio Grande County lies within the San Luis Valley — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Rio Grande County holds more than one microclimate.
Soils and elevations shift across Rio Grande 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 Rio Grande County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Rio Grande County — the short answer
Rio Grande County, Colorado: USDA zone 5b, about 107 days between hard freezes, across 584K acres.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jun 4
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Sep 19
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~107
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 584K 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 5b is Rio Grande County's average, not your lot's — a low corner or a tree line moves it. Against Rio Grande County's 107-day season, see what your own ground reads.
Heat in Rio Grande County
Across a year, Rio Grande County accumulates about 210 growing degree days above 50°F, about 1,622 fewer than the middle Colorado county — ahead of 3 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 Rio Grande County
Across Rio Grande County, the ground is predominantly Aridisols, where Norte, Luhon, and Garita are the most extensive named soil series. The soil is generally well drained with a loam surface. Topsoil pH runs about 7.5–8.2, slightly alkaline. Rainfall drains through hydrologic group B soils.
Soil order
Aridisols
Drainage
Well drained
Hydric soils
10%
Soil still varies lot by lot — soil types explained.
How the ground varies across Rio Grande County
The USDA soil survey maps 48% of Rio Grande County as well drained — but another 50% drains differently: 25% moderately well drained, 11% poorly drained.
Norte is the most extensive named soil at 12% of mapped acres, then Luhon (9%) and Garita (8%).
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 Rio Grande County
Each reading below is measured for Rio Grande 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 Rio Grande County are well drained, in hydrologic group B — 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 Rio Grande County runs about pH 7.5–8.2, on the alkaline side.
Many vegetables cope, but acid-lovers like blueberries struggle, and iron and manganese lock up above about pH 7.5 — leaves yellow between the veins even in rich soil.
Elemental sulfur and generous organic matter lower pH slowly for the beds that need it; test first so you add only what the soil actually calls for.
USDA NRCS SSURGO
Season length
MeasuredRio Grande County runs about 107 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
MeasuredRio Grande County 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 Rio Grande County is in
Rio Grande County spans 2 EPA Level III ecoregions — Southern Rockies (59%) and Arizona/New Mexico Plateau (41%). Which one your land falls in changes what grows wild there and how the ground behaves, and a county-wide answer cannot tell you which.
What Grows in Rio Grande County
We scored all 1,086 plants against Rio Grande County's own USDA zone 5b and its own 107-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 Rio Grande County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around May 7; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jun 4 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 19 — 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.
Documented around Rio Grande County
- monarch butterfly128 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Rio Grande County
USGS estimates 8,144 lb of Glyphosate on Rio Grande County farmland in 2019, its largest by weight, ahead of Metolachlor-s (5,532 lb) and Metolachlor & Metolachlor-s (5,532 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Rio Grande County — and how to grow with it.
We checked the federal record across Rio Grande County — 217 documented sites across 7 of the 9 source types we track.
The most significant on record: 2 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Rio Grande 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 Rio Grande County
Closest first, across Rio Grande County. Listing isn't leaking, and distance isn't exposure.
- Decatur Ne DistrictMining · 4.7 mi
- Guadaloupe Claims GroupMining · 4.9 mi
- Miser MineMining · 4.9 mi
- Guadaloupe MineMining · 4.9 mi
- VALLEY CITIZENS FOR HEALTHCARE INC DBA RIO GRANDE HOSPITALBrownfields · 6.8 mi
- US EPA FUND-LEAD SUPERFUND SITE/SUMMITVILLE MINEToxics Release Inventory · 8.2 mi
- Summitville DistrictMining · 8.6 mi
- Reynolds MineMining · 8.7 mi
- Summitville MineMining · 8.7 mi
- Missionary TunnelMining · 8.8 mi
- Narrow Gauge MineMining · 8.9 mi
- Dexter TunnelMining · 8.9 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Rio Grande 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 Rio Grande County.
Sources Checked
across Rio Grande County
Severity Distribution
across Rio Grande County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Rio Grande County, two things run higher than the national average across Rio Grande County — Mining (39 sites) and Nitrate (80 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.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Check your specific parcel in Rio Grande 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 Rio Grande County average
Your land is one point inside Rio Grande County
Everything above resolves to Rio Grande County as a whole — one PHZM band and one county frost record, read across 584K 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 Rio Grande County Average
Rio Grande County Average
- ●USDA Zones 5b, averaged across Rio Grande County
- ●One soil character for all of Rio Grande County
- ●Frost dates read at Rio Grande County's scale: Jun 4 to Sep 19
YOUR Parcel
- ✓Your exact zone, not Rio Grande County's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Rio Grande County
Pull a site-specific report for your exact address in Rio Grande County, Colorado — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Rio Grande County averages can't show:
We read public map data around Rio Grande County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Rio Grande County average
How we know this about Rio Grande 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 Rio Grande County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Rio Grande County
When does frost risk typically end in Rio Grande County?
The last hard freeze (28°F) in Rio Grande County typically lands around Jun 4, 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 Jun 25.
How long is the growing season in Rio Grande County?
Measured between 28°F hard freezes, Rio Grande County sees about 107 frost-free days — roughly Jun 4 through Sep 19, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 25 to Sep 5, about 72 days.
Is the soil safe to grow vegetables in Rio Grande County?
The federal record around Rio Grande County runs heavier than most — 217 documented sites, mostly Nitrate entries (80), the nearest Mining record about 4.7 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 Rio Grande County?
With about 107 frost-free days between hard freezes, Rio Grande 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 135 to 163 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the Jun 4 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Rio Grande County's scale — its 5b band and its 107-day season. Your yard writes its own version of Rio Grande 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 Rio Grande County’s own scale
9 of the readings below were taken at Rio Grande County's own scale — its own ~107-day span between 28°F freezes, the 3 most extensive soil series mapped here and 217 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Rio Grande County's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Rio Grande County's own 28°F hard-freeze dates and its ~107-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Rio Grande CountyUSDA NRCS SSURGO
- 217 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Mining record about 4.7 miles outFederal environmental registers
- Rio Grande County's boundary and the 583,652 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~107-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Rio Grande County spans, Southern Rockies the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Rio Grande County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Rio Grande County farmland, and roughly how muchUSGS NAWQA EPest county estimates
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 Rio Grande County — the ~107 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 Rio Grande County's 583,652 acreswhy one lot differs from the next →
- Which of those 217 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 Rio Grande Countyread your own land →