The San Luis Valley spans USDA hardiness zones 4b-5b — room for a real mix of vegetables, fruit, and perennials matched to the local frost calendar.
The San Luis Valley is Colorado's high, cold intermountain basin — short frost-free seasons and hard winters — yet Rio Grande irrigation makes it one of the state's most important farming areas, famous for potatoes and barley. The conditions favor colorado blue spruce, tomato, chokecherry, and apple, among others — though every individual site edits that list with its own soil, sun, and drainage.
The San Luis Valley spans Colorado.
Your yard isn't all of the San Luis Valley.
The San Luis Valley spans USDA zones 4b-5b, but your parcel sits in exactly one — and slope, tree cover, and low spots nudge it further. 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 Luis Valley — soil, climate, flood, and parcel records. How we handle your address.
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The San Luis Valley — the short answer
The San Luis Valley: USDA zones 4b-5b, 107–138 frost-free days depending where in it you stand, in Colorado.
- USDA zones
- 4b-5b
- USDA PHZM 2023, aggregated over the footprint
- Shortest season here
- 107 days
- NOAA Regional Climate Centers ACIS, 1991-2020 — Rio Grande County
- Counties
- 6
- US Census TIGER/Line 2025
- Region type
- County cluster
- Growable Ground growing-region registry
Region boundary: Growable Ground growing-region registry — curated county clusters, EPA Level III ecoregions, and town clusters drawn finer than any county. The season figure is this region's own record, measured across its 6 member counties, not a state or national average.
Hardiness Zone Range
The San Luis Valley is not one growing season
One answer for the San Luis Valley averages 6 counties whose growing seasons are 31 days apart — from 107 frost-free days in Rio Grande County to 138 in Costilla County. That is the same region, measured the same way, in the same years. Which end of it your land sits nearer decides what finishes before the first hard freeze.
The middle half of 6 counties runs 114–137 days, with a median of 132 days — a 31-day span end to end.
Measured across 6 member counties, each carrying its own 28°F normal. NOAA Regional Climate Centers ACIS, 1991-2020. A member with no own record is absent from the range rather than counted as zero — nothing here is interpolated to the region. Your own site sits somewhere inside this range; a parcel report resolves where.
Where the line runs inside the San Luis Valley
The middle half of the San Luis Valley runs 114–137 frost-free days, and 3 of its 6 counties sit outside that — 2 on the short side, 1 on the long. A regional planting date describes the middle well and the ends poorly, which is worth knowing before you follow one.
Under 114 frost-free days
2 counties
- Rio Grande County · 107 days
- Mineral County · 109 days
The end of the region that sets the planting calendar — start seed indoors here and the season stretches to meet the crop.
114–137 frost-free days
3 counties
0 of 3 shown
The middle half of the region, and the part a single regional season describes well.
Over 137 frost-free days
1 county
- Costilla County · 138 days
Long enough for a second succession of a quick crop after the first comes out.
Each county is placed by its OWN 28°F frost-free normal (NOAA Regional Climate Centers ACIS, 1991-2020), the same figure its own guide page publishes. Elevation, slope and cold-air drainage move a site within its county as well — which is the part only your address resolves.
What Grows in the San Luis Valley
All 1 of the plants below that publish a season requirement clear even Rio Grande County’s 107 frost-free days — so on season alone, this grid works at both ends of the region. The 31-day spread still decides how far past this list you can push, and how early you can start.
Plants matched to the San Luis Valley's USDA zones 4b-5b, ordered by how much hardiness margin each has across the region — the ones with room to spare at both ends of this band lead. Each links to its full growing profile.
Native Plants of the San Luis Valley
Plants the USDA PLANTS Database documents as native and present in this region’s state, kept only where the published hardiness range meets the San Luis Valley’s USDA zones 4b-5b — closest range match first. Presence is recorded by state, so a plant can be documented across the state and still be scarce in your corner of the region.
The ground across the San Luis Valley
The USDA soil survey maps this ground county by county. These are those records weighted by land area across five member counties — this region’s own profile, not a state figure.
The ground is predominantly Aridisols, at 39% of mapped acres, followed by Mollisols (27%), Entisols (17%) and Alfisols (12%). Six soil orders appear somewhere inside the footprint, which is the honest reason a regional soil answer only goes so far. The most extensive named soils are Travelers, Garita, and Hooper.
65% of those acres are well drained, and another 9% moderately well drained, 8% poorly drained. Topsoil pH runs 6.6–8.8 between the lowest and the highest county on record.
Soil order
Aridisols
Drainage
Well drained
Topsoil pH
6.6–8.8
Hydric soils
7%
Soil changes across a driveway, so which of these your own ground sits on is a parcel question rather than a regional one. Rio Grande County holds the most wetland ground here, at 10% — soil types explained.
USDA NRCS SSURGO via Soil Data Access · 5 of 6 footprint counties carry a summarizable record; the rest are absent from these figures rather than estimated.
What this means for growing in the San Luis Valley
The soil survey reads this ground county by county, and the readings above are those records summed across the San Luis Valley. Here is what they mean for a garden here — and the move an experienced grower makes about each one.
Drainage
From county records65% of the mapped acres across the San Luis Valley are well drained — ground that drains quickly. That is area-weighted across all five of its mapped counties.
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
From county recordsTopsoil across the San Luis Valley runs pH 6.6–8.8 — alkaline in four of its five counties.
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
Safe to Grow Here?
What the federal record shows across the San Luis Valley — and how to grow with it.
Across the San Luis Valley's 6 counties the federal record holds 1,239 documented sites, mostly Mining (512), Nitrate (408) and Underground Storage Tanks (245). The heaviest single county is Saguache County, with 461.
That is a regional count, not a reading of any one lot — proximity to a documented site is information, not a diagnosis. Open the map outlined to the San Luis Valley to see which records sit where you actually grow.
Sources Checked
Summed across the 6 counties in the San Luis Valley
A note from Gnorman
What an experienced grower watches for around here
In and around the San Luis Valley, two things run higher than the national average across the 6 counties in the San Luis Valley — Mining (512 sites) and Nitrate (408 sites). That's not a problem with your land — it's information about 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).
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
Your land is one point inside the San Luis Valley
Everything above resolves to the San Luis Valley as a whole — a footprint whose own counties record seasons 31 days apart, and hardiness across zones 4b-5b. Your parcel sits at one point in that range, not in the middle of it. 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 region 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 regional average.
Your Lot vs the San Luis Valley Average
San Luis Valley Average
- ●USDA Zones 4b-5b, averaged across San Luis Valley
- ●One soil character for all of San Luis Valley
- ●State-average frost dates
YOUR Parcel
- ✓Your exact zone, not San Luis Valley's 4b-5b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in the San Luis Valley
Pull a site-specific report for your exact address in the San Luis Valley — soil, sun, drainage, frost risk, contamination, and scored plant recommendations.
Three things about your lot that San Luis Valley averages can't show:
We read public map data around The San Luis Valley — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the San Luis Valley average
How we know this about the San Luis Valley
The boundary: a cluster of neighboring counties. Growing regions have no official boundary, so this footprint is our published one, and every figure on this page was measured over the counties inside it rather than borrowed from the state around it.
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, aggregated across the footprint; the growing season from NOAA Regional Climate Centers ACIS 1991–2020 28°F normals, read at each member’s own record; boundaries from US Census TIGER/Line 2025; the contamination record from the federal sources named in that beat above; the soil from the USDA NRCS SSURGO survey, read at each member county’s own record and weighted to this footprint by land area. Where a member carries no record of its own, it is absent from the figure rather than filled in.
Common questions about the San Luis Valley
What hardiness zone is the San Luis Valley?
The San Luis Valley spans USDA hardiness zones 4b-5b, aggregated from the USDA Agricultural Research Service Plant Hardiness Zone Map 2023 across the region's counties. Zones reflect average annual extreme minimum temperatures from 1991–2020 data.
How long is the growing season in the San Luis Valley?
Measured between 28°F hard freezes, the San Luis Valley's counties mostly run 114 to 137 frost-free days, median 132 (NOAA Regional Climate Centers ACIS, 1991–2020, over 6 member counties). That 23-day spread is the honest read — no single season describes 6 counties, and each county guide below carries its own.
When does frost risk end in the San Luis Valley?
Across the San Luis Valley, the middle half of member counties see their last 28°F hard freeze between May 18 and Jun 1 (median May 20), and their first fall freeze between Sep 23 and Sep 30. Those are hard freezes, not the last light frost: tender transplants wait for about Jun 10, and elevation decides which end of a 14-day spread you garden in.
What grows well in the San Luis Valley?
The San Luis Valley's conditions suit plants such as Colorado Blue Spruce, Tomato, Chokecherry, Apple, Raspberry, Hops. What actually thrives on any one site still turns on its specific soil, sun, and drainage — we score each plant against the real conditions at your address.
How is the San Luis Valley defined?
The San Luis Valley is defined here as a curated cluster of 6 neighboring counties that share a growing character. Growing regions have no official boundary, so this footprint is our published one — every county in it is named on this page.
Which states does the San Luis Valley cover?
The San Luis Valley spans Colorado. Each state's full growing guide is linked on this page.
What other growing regions cover the same states?
High Plains, Colorado High Country (Central Rockies), Front Range, Arkansas River Valley (Rocky Ford–Pueblo Corridor), Four Corners / Southwest Colorado, and Uncompahgre Valley share at least one state with the San Luis Valley. Growing regions overlap and interlock — a single address can sit inside more than one, which is why the precise read is always the parcel, not the region.
What this page reads at the San Luis Valley’s own scale
6 of the readings below were taken at the San Luis Valley's own scale — the zone 4b-5b band across its footprint, a median 132-day season across its 6 counties and 1,239 documented federal contamination records across its 6 counties, 461 of them in Saguache County alone; one is borrowed from a wider read, named and linked below.
Measured here
- The USDA hardiness band 4b-5b aggregated across all 6 counties in the footprintUSDA PHZM 2023
- The boundary itself — the 6 counties this region is curated fromGrowable Ground subregion registry
- The growing character that makes this region distinct from the states it crossesGrowable Ground subregion registry
- The 28°F season across the footprint — the middle half of its 6 counties run 114 to 137 frost-free days, median 132NOAA Regional Climate Centers ACIS, 1991-2020
- The federal contamination record over the whole footprint — 1,239 documented federal contamination records across its 6 counties, 461 of them in Saguache County aloneEPA, USGS and USDA federal site records
- The soil order mix across the footprint — 39% Aridisols, topsoil pH 6.6–8.8, area-weighted across its 5 mapped countiesUSDA NRCS SSURGO
Inherited from a wider read
- The candidate plant list — its state's curated sets, merged and filtered to zones 4b-5bfrom Colorado
What this page can’t tell you
- Which end of the 23-day range your ground sits at — 114 days at one extreme, 137 at the other, decided mostly by elevationfrost dates explained →
- Which of those soils your own ground sits on — the survey maps them county-wide, and they change across a drivewaysoil types explained →
- The soil pH, drainage, sun hours, and frost pockets on one specific lotwhy one lot differs from the next →
Explore the San Luis Valley
State growing guides
Counties in this region
Other growing regions across Colorado
A semi-arid shortgrass tableland of deep soils and big sky, where wind, low rainfall, and irrigation shape dryland wheat, sorghum, and resilient gardens.
Colorado's highest gardens sit at 7,500–10,000+ feet, where frost can land in any month and the honest growing window runs 85–141 days across the region's counties — a span a single county figure hides at both ends. Because county centroids average the alpine slopes upward, the committed town data runs colder than the county page: Crested Butte gardens at zone 3b, Gunnison at 4a, Leadville sees roughly 84 frost-free days. This is the short-season opposite pole of the San Luis high-desert basin, and a completely different regime from the Front Range (169 frost-free days) or the Grand Valley (209) — season extension, cold-hardy varieties, and month-round frost vigilance drive every planting decision here.
Colorado's high, dry urban corridor at the foot of the Rockies — intense sun, alkaline soils, and a short season that rewards cold-hardy, drought-wise gardening.
Colorado's irrigated warm-season pocket. The lower Arkansas River bottomland east of the mountains runs a 178-to-191-frost-free-day season in zones 5b-6a — long and warm enough that Rocky Ford built a cantaloupe-and-watermelon reputation and Pueblo its green chile. That specialty-crop identity is nothing like the dryland shortgrass wheat and sorghum of the surrounding High Plains; what sets a parcel apart here is water. The ditch-irrigated valley floor grows heat-loving melons and chiles the unwatered tableland just above it cannot.
Southwest Colorado's Four Corners country grows on high-desert mesas at roughly 6,000-7,000 ft, where zone 6a-6b winters meet a warm-day/cool-night rhythm and a late-summer monsoon — a climate distinct from both the lower, warmer valleys of the northern Western Slope and the frost-pocket high country above it. The 146-168 frost-free days around Durango, Cortez, Mancos, and Pagosa Springs favor short-to-mid-season crops, and the Cortez-Dove Creek belt beside Mesa Verde is legendary dryland pinto-bean country (Dove Creek bills itself the "Pinto Bean Capital of the World").
The Uncompahgre River valley floor from Montrose past Olathe down to Delta, where Bureau of Reclamation irrigation and a warm 6a-to-7a valley climate stretch the frost-free season from about 130 days upvalley near Montrose to 189 days near Delta.