Costilla County, in Colorado, sits in USDA hardiness zone 5b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
On paper, cabbage, cranberry, lavender, and collard greens all suit these conditions — on the ground, soil, sun, and drainage make the final call.
Costilla 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
Costilla County holds more than one microclimate.
Soils and elevations shift across Costilla 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 Costilla County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Costilla County — the short answer
Costilla County, Colorado: USDA zone 5b, about 138 days between hard freezes, across 786K acres.
- USDA zone
- 5b
- USDA PHZM 2023
- Last hard freeze (28°F)
- May 15
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Sep 30
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~138
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 786K 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 Costilla County's average, not your lot's — a low corner or a tree line moves it. Against Costilla County's 138-day season, see what your own ground reads.
Heat in Costilla County
Across a year, Costilla County accumulates about 1,275 growing degree days above 50°F, about 557 fewer than the middle Colorado county — ahead of 25 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 Costilla County
Across Costilla County, the ground is predominantly Aridisols, where McGinty, Cososa, and Tolvar are the most extensive named soil series. The soil is generally well drained with a fine sandy loam surface. Topsoil pH runs about 6.6–7.7, neutral. Rainfall drains through hydrologic group B soils.
Soil order
Aridisols
Drainage
Well drained
Hydric soils
2%
Soil still varies lot by lot — soil types explained.
How the ground varies across Costilla County
The USDA soil survey maps 82% of Costilla County as well drained — but another 15% drains differently: 8% somewhat excessively drained, 4% poorly drained.
McGinty is the most extensive named soil at 12% of mapped acres, then Cososa (11%) and Tolvar (9%).
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 Costilla County
Each reading below is measured for Costilla 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 Costilla 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 Costilla County runs about pH 6.6–7.7, 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
MeasuredCostilla County runs about 138 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
MeasuredCostilla 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 Costilla County is in
Costilla County spans 2 EPA Level III ecoregions — Arizona/New Mexico Plateau (51%) and Southern Rockies (49%). 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 Costilla County
We scored all 1,086 plants against Costilla County's own USDA zone 5b and its own 138-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 Costilla County?
For most of the year, no — what changes is which crops still fit the days remaining. Cool-season crops can go in from around Apr 17; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near May 15 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 30 — 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 Costilla County
- monarch butterfly1 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Costilla County
USGS estimates 16,427 lb of Glyphosate on Costilla County farmland in 2019, its largest by weight, ahead of Metolachlor-s (5,534 lb) and Metolachlor & Metolachlor-s (5,534 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 Costilla County — and how to grow with it.
We checked the federal record across Costilla County — 72 documented sites across 5 of the 9 source types we track.
The most significant on record: 1 Toxics Release Inventory facility. Active industrial facilities reporting chemical releases to air, water, and land.
There's a meaningful federal record across Costilla County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Costilla County
Closest first, across Costilla County. Listing isn't leaking, and distance isn't exposure.
- CC03207222CBANitrate · 1.9 mi
- Centennial School District R1Underground Storage Tanks · 5.0 mi
- San Luis MineMining · 5.0 mi
- El Plomo DistrictMining · 5.2 mi
- Central OilUnderground Storage Tanks · 5.2 mi
- Zegob StoreUnderground Storage Tanks · 5.3 mi
- Unnamed ProspectMining · 5.4 mi
- San Luis TexacoUnderground Storage Tanks · 5.4 mi
- San Luis Custom CyclesUnderground Storage Tanks · 5.5 mi
- Speedway GarageUnderground Storage Tanks · 5.5 mi
- Gus ServiceUnderground Storage Tanks · 5.6 mi
- El Plomo MineMining · 5.7 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Costilla 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 Costilla County.
Total Sites
72
across Costilla County
Risk Level
Elevated
Highest-severity
1 Toxics Release Inventory facility
Sources Checked
across Costilla County
Severity Distribution
across Costilla County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Costilla County, two things run higher than the national average across Costilla County — Mining (21 sites) and Nitrate (22 sites). 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.
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 Costilla 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 Costilla County average
Your land is one point inside Costilla County
Everything above resolves to Costilla County as a whole — one PHZM band and one county frost record, read across 786K 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 Costilla County Average
Costilla County Average
- ●USDA Zones 5b, averaged across Costilla County
- ●One soil character for all of Costilla County
- ●Frost dates read at Costilla County's scale: May 15 to Sep 30
YOUR Parcel
- ✓Your exact zone, not Costilla County's 5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Costilla County
Pull a site-specific report for your exact address in Costilla County, Colorado — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Costilla County averages can't show:
We read public map data around Costilla County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Costilla County average
How we know this about Costilla 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 Costilla County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Costilla County
When does frost risk typically end in Costilla County?
The last hard freeze (28°F) in Costilla County typically lands around May 15, 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 5.
How long is the growing season in Costilla County?
Measured between 28°F hard freezes, Costilla County sees about 138 frost-free days — roughly May 15 through Sep 30, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 5 to Sep 16, about 103 days.
Is the soil safe to grow vegetables in Costilla County?
The federal record around Costilla County is a meaningful one — 72 documented sites, mostly Underground Storage Tanks entries (26), the nearest Nitrate record about 1.9 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
How do gardeners stretch the season in Costilla County?
With about 138 frost-free days between hard freezes, Costilla 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 166 to 194 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the May 15 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Costilla County's scale — its 5b band and its 138-day season. Your yard writes its own version of Costilla 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 Costilla County’s own scale
9 of the readings below were taken at Costilla County's own scale — its own ~138-day span between 28°F freezes, the 3 most extensive soil series mapped here and 72 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Costilla County's own USDA hardiness band, zones 5bUSDA PHZM 2023
- Costilla County's own 28°F hard-freeze dates and its ~138-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Costilla CountyUSDA NRCS SSURGO
- 72 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Nitrate record about 1.9 miles outFederal environmental registers
- Costilla County's boundary and the 785,659 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 5b and a ~138-day seasonGrowable Ground crop-matching engine
- The 2 ecoregions Costilla County spans, Arizona/New Mexico Plateau the largestUS EPA Level III Ecoregions
- Open occurrence records documented in Costilla County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Costilla 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 Costilla County — the ~138 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 Costilla County's 785,659 acreswhy one lot differs from the next →
- Which of those 72 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 Costilla Countyread your own land →