Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 80108 — Castle Rock, CO

ZIP code 80108 (Castle Rock, Douglas County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is May 9 and the first fall frost October 2.

Where ZIP 80108 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone5b−15 to −10 °F
Coldest night−26.1 to −23.3 °C
Last frostMay 9
First frostOct 2
2012 zone5b

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Castle Rock, CO…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Castle Rock, CO

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 9median — 50% chance of a later frost
Safe for tender plantsMay 24only 10% chance of frost after
First fall frostOctober 2median — 10% chance by Sep 17
Growing season143 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 1 and returns around October 12.

From the NOAA station Castle Rock, CO — 4 miles away, elevation 6,185 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 80108

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 28 – Apr 11
SpinachSow outdoors · Mar 28 – Apr 18
Broccoli, cabbageStart indoors · Feb 28 – Mar 14
Broccoli, cabbageTransplant · Apr 18 – May 2
Onion setsPlant outdoors · Apr 11 – Apr 25
PotatoesPlant outdoors · Apr 18 – May 2
LettuceSow outdoors · Apr 11 – Apr 25
Carrots, beetsSow outdoors · Apr 18 – May 2
TomatoesStart indoors · Mar 14 – Mar 28
TomatoesTransplant · May 16 – May 30
Peppers, eggplantStart indoors · Feb 28 – Mar 14
Peppers, eggplantTransplant · May 23 – Jun 6
BeansSow outdoors · May 16 – May 30
Sweet cornSow outdoors · May 16 – May 30
Cucumbers, squashSow outdoors · May 16 – May 30
Fall lettuce, spinachSow outdoors · Aug 7 – Aug 21
GarlicPlant cloves · Sep 18 – Oct 23
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 9) and first fall frost (Oct 2) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 80108 came on Feb 20 — 32 days earlier than the 1991–2020 average (Mar 24).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 5b in Colorado

546 plants native to the lower 48 states, recorded in Colorado, and rated by the USDA to survive −15 °F or colder — the bottom of zone 5b. Each links to its USDA PLANTS profile.

Trees 27

American elm120 ft · blooms early spring · medium shade tolerance · to −46 °Fbalsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fblack locust60 ft · blooms spring · high shade tolerance · to −37 °Fblack walnut100 ft · blooms late spring · high shade tolerance · to −28 °Fblack willow100 ft · blooms early spring · high shade tolerance · to −58 °Fblue spruce100 ft · blooms late spring · medium shade tolerance · to −38 °F

Shrubs 98

alderleaf mountain mahogany15 ft · blooms late spring · medium shade tolerance · to −41 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican plum24 ft · blooms mid spring · high shade tolerance · to −38 °Fantelope bitterbrush6 ft · blooms early spring · medium shade tolerance · to −36 °FApache plume6 ft · blooms late spring · high shade tolerance · to −23 °F

Wildflowers & perennials 246

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine aster0.3 ft · blooms early summer · medium shade tolerance · to −28 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °FAmerican bistort1.5 ft · blooms mid spring · high shade tolerance · to −38 °F

Grasses 163

Alaska oniongrass3 ft · blooms mid spring · low shade tolerance · to −33 °Falkali cordgrass3 ft · blooms late summer · high shade tolerance · to −38 °Falkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °FAlpine Meadow-Foxtail0.5 ft · blooms mid spring · medium shade tolerance · to −33 °Falpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °Fanalogue sedge1.5 ft · blooms late spring · medium shade tolerance · to −38 °F

Vines 3

riverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °FVirginia creeper1 ft · blooms late spring · medium shade tolerance · to −28 °Fwestern white clematis1 ft · blooms mid summer · medium shade tolerance · to −38 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Castle Rock, CO.

Soil in Castle Rock, CO

The soil mapped at the center of ZIP 80108 is Fondis — loam, well drained.

TextureLoama good balance for most vegetables
pH7.2neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter3%moderate
Hydrologic groupCwater soaks in slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Fondis-Kutch association.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 80108; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Castle Rock, CO

Summer high86 °Faverage high, July
Winter low18 °Faverage low, January
Hot days23days a year at 90 °F or more
Freezing nights167nights a year at 32 °F or less
Growing degree days2,491base 50 °F — the season’s usable heat
Longest day14 h 57 mindaylight on June 21
Shortest day9 h 23 mindaylight on December 21
Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully
Precipitation18.2 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 46 °F, low 18 °F 46°18° JanFebruary: average high 47 °F, low 20 °F 47°20° FebMarch: average high 54 °F, low 27 °F 54°27° MarApril: average high 59 °F, low 33 °F 59°33° AprMay: average high 68 °F, low 42 °F 68°42° MayJune: average high 80 °F, low 51 °F 80°51° JunJuly: average high 86 °F, low 56 °F 86°56° JulAugust: average high 84 °F, low 55 °F 84°55° AugSeptember: average high 77 °F, low 47 °F 77°47° SepOctober: average high 65 °F, low 35 °F 65°35° OctNovember: average high 54 °F, low 26 °F 54°26° NovDecember: average high 46 °F, low 18 °F 46°18° Dec

Precipitation by month inches

0″1″2″3″January: 0.59 in precipitation 0.6 JanFebruary: 0.44 in precipitation 0.4 FebMarch: 1.48 in precipitation 1.5 MarApril: 2.18 in precipitation 2.2 AprMay: 2.64 in precipitation 2.6 MayJune: 1.99 in precipitation 2.0 JunJuly: 2.32 in precipitation 2.3 JulAugust: 2.48 in precipitation 2.5 AugSeptember: 1.44 in precipitation 1.4 SepOctober: 1.21 in precipitation 1.2 OctNovember: 0.80 in precipitation 0.8 NovDecember: 0.59 in precipitation 0.6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Castle Rock, CO (4 mi away); precipitation: Castle Rock 4.6 Nnw, CO (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

4 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

801345b
Parker, CO · 5 mi
801095b
Castle Rock, CO · 6 mi
801246a
Lone Tree, CO · 6 mi
801306a
Littleton, CO · 7 mi
801315b
Louviers, CO · 9 mi
801126a
Englewood, CO · 9 mi
801266a
Littleton, CO · 9 mi
801045b
Castle Rock, CO · 10 mi

All 3 ZIP codes in Castle Rock → · Colorado planting zones →

Questions about 80108

What planting zone is ZIP code 80108?

ZIP code 80108 (Castle Rock, CO) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Castle Rock, CO?

The median last spring frost (32 °F) near 80108 is May 9; after May 24 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Castle Rock station.

When is the first frost in Castle Rock, CO?

The median first fall frost near 80108 is October 2, giving a median frost-free growing season of 143 days.

When should I plant tomatoes in 80108?

Start tomato seeds indoors around Mar 14 – Mar 28 and set transplants outside around May 16 – May 30, one to three weeks after the median last frost.

How much rain and snow does 80108 get?

About 18.2 inches of precipitation a year (NOAA 1991–2020 normals, Castle Rock 4.6 Nnw station).

How hot do summers get in Castle Rock, CO?

The average high peaks at 86 °F in July, with about 23 days a year at 90 °F or more.

What kind of soil does 80108 have?

The USDA soil survey maps Fondis at the center of ZIP 80108: loam, well drained, pH about 7.2 (neutral).

Did spring come early in Castle Rock, CO in 2026?

Spring leaf-out near 80108 came on Feb 20 in 2026, 32 days earlier than the 1991–2020 average (Mar 24), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Castle Rock, CO?

Intermediate onions: the longest day near 80108 is 14 h 57 min, so day-neutral types bulb best; long-day varieties may not bulb fully.