Silverthorne, Colorado, sits in USDA hardiness zone 4b — a range where zone-matched perennials and frost-aware annual timing set what succeeds.
Among the crops suited to this profile: zucchini, cranberry, cilantro, and pumpkin. The site-level story — soil, sun, drainage — decides the rest.
Even in Silverthorne, 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 Silverthorne 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 Silverthorne — soil, climate, flood, and parcel records. How we handle your address.
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Silverthorne — the short answer
Silverthorne, Colorado: USDA zone 4b, about 90 days between hard freezes, across 3K acres of town.
- USDA zone
- 4b
- USDA PHZM 2023
- Last hard freeze (28°F)
- Jun 9
- NOAA 1991–2020 Climate Normals, 28°F — this town
- First hard freeze (28°F)
- Sep 7
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Days between freezes
- ~90
- NOAA 1991–2020 Climate Normals, 28°F — this town
- Town area
- 3K 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 4b is Silverthorne's average, not your lot's — a low corner or a tree line moves it. Against Silverthorne's 90-day season, see what your own ground reads.
Soil varies lot by lot — soil types explained.
What this means for growing in Silverthorne
Each reading below is measured for Silverthorne itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Season length
MeasuredSilverthorne runs about 90 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
MeasuredSilverthorne 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 Silverthorne is in
Silverthorne sits in the Southern Rockies — EPA Level III, inside the wider Northwestern Forested Mountains. That is read at Silverthorne's own centroid rather than borrowed from Summit County.
What Grows in Silverthorne
Every plant below cleared Silverthorne's own zone 4b and its 90-day season. Each card opens that plant's Colorado profile. How we score.
Is it too late to plant in Silverthorne?
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 12; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Jun 9 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Sep 7 — long-season crops need about 90 days of runway, quick greens only 30. Short seasons reward decisiveness — quick-maturing varieties late, hardy greens under cover, and next year’s garlic in the ground before it closes.
What's on the federal record near Silverthorne
Closest first, within ~10 miles of Silverthorne. Listing isn't leaking, and distance isn't exposure.
- SC00407835AAB-SILVERTHORNE WWTPNitrate · 1900 ft
- SC00407836CBC-GOLDEN EAGLENitrate · 2600 ft
- SC00407836CDB00Nitrate · 0.7 mi
- Skelly-texaco StationUnderground Storage Tanks · 1.0 mi
- Dillon Ranger StaUnderground Storage Tanks · 1.0 mi
- Kum & Go #907Underground Storage Tanks · 1.1 mi
- SC00507801BCD-ELKS LODGENitrate · 1.1 mi
- George & Susy CulbreathUnderground Storage Tanks · 1.5 mi
- TARGET T1525Brownfields · 1.7 mi
- CVS PHARMACY #16855Brownfields · 1.7 mi
- Summit County Operations Center (Xcel Energy)Underground Storage Tanks · 1.8 mi
- PSCO - SUMMIT CO OPSBrownfields · 1.8 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Silverthorne'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 Silverthorne.
Total Sites
171
within ~10 miles of Silverthorne
Risk Level
High
Highest-severity
2 Superfund sites (none NPL-listed)
Sources Checked
within ~10 miles of Silverthorne
Severity Distribution
within ~10 miles of Silverthorne
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Silverthorne, two things run higher than the national average within ~10 miles of Silverthorne — Mining (13 sites) and Nitrate (56 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 Silverthorne
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 Silverthorne average
Your land is one point inside Silverthorne
Everything above resolves to Silverthorne as a whole — one PHZM band and one 28°F frost record, read across 3K 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 Silverthorne Average
Silverthorne Average
- ●USDA Zones 4b, averaged across Silverthorne
- ●One soil character for all of Silverthorne
- ●Frost dates read at Silverthorne's scale: Jun 9 to Sep 7
YOUR Parcel
- ✓Your exact zone, not Silverthorne's 4b
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your specific parcel in Silverthorne
Pull a site-specific report for your exact address in Silverthorne, Colorado — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Silverthorne averages can't show:
We read public map data around Silverthorne — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Silverthorne average
How we know this about Silverthorne
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 Silverthorne’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 Silverthorne
When does frost risk typically end in Silverthorne?
The last hard freeze (28°F) in Silverthorne typically lands around Jun 9, 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 30.
When is the first frost in Silverthorne?
The first hard freeze (28°F) in Silverthorne typically arrives around Sep 7, per NOAA 1991–2020 climate normals — the point tender summer crops finish. Lighter frosts run ahead of it, near Aug 24, so the watching starts about Aug 8 — about 90 days after the spring freeze cleared.
How long is the growing season in Silverthorne?
Measured between 28°F hard freezes, Silverthorne sees about 90 frost-free days — roughly Jun 9 through Sep 7, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Jun 30 to Aug 24, about 55 days.
Is the soil safe to grow vegetables in Silverthorne?
The federal record around Silverthorne runs heavier than most — 171 documented sites, mostly Underground Storage Tanks entries (73), the nearest Nitrate record about 0.4 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 Silverthorne?
With about 90 frost-free days between hard freezes, Silverthorne 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 118 to 146 days — and cold frames or low tunnels buy more. Starting transplants indoors ahead of the Jun 9 hard-freeze normal stretches the season without touching the calendar.
Everything above is measured at Silverthorne's scale — its 4b band and its 90-day season. Your yard writes its own version of Silverthorne'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 Silverthorne’s own scale
6 of the readings below were taken at Silverthorne's own scale — its own ~90-day season between 28°F freezes, the 2,598 acres it covers and 171 documented sites around it; 4 are borrowed from a wider read, named and linked below.
Measured here
- Silverthorne's own USDA hardiness band, zones 4bUSDA PHZM 2023
- Silverthorne's own 28°F hard-freeze dates, about Jun 9 and Sep 7 and the ~90-day span between themNOAA 1991–2020 Climate Normals
- 171 documented contamination sites on the federal record near Silverthorne, the closest Nitrate record about 0.4 miles out from the town centreFederal environmental registers
- Silverthorne's boundary and the 2,598 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 4b and a ~90-day seasonGrowable Ground crop-matching engine
- The ecoregion at Silverthorne's own centroid, the Southern RockiesUS EPA Level III Ecoregions
Inherited from a wider read
- Soil character — no town-scale survey exists, so Silverthorne's 2,598 acres read through its county's SSURGO summaryfrom Summit County
- Growing-degree days and winter chill — measured county-wide only, so the county page carries themfrom Summit 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 Summit County
What this page can’t tell you
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Silverthorne's 2,598 acreswhy one lot differs from the next →
- Which side of Silverthorne you're on — a low spot frosts first and a south wall warms early, and one normal is being asked to speak for all 2,598 acresreading your own microclimate →
- How close that record sits to YOUR lot — the closest Nitrate record about 0.4 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 Silverthorne-wide figureread your own land →