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

Planting zone for Broomfield, CO

Broomfield, CO is in USDA zone 6a across its 4 ZIP codes. The median last spring frost is May 2 and the first fall frost October 11.

Broomfield on the zone map

Outlined: its 3 ZIP code areas · 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.

Zone6a−10 to −5 °F
ZIP codes4
Last frostMay 2
First frostOct 11
Growing season160 days

6a 4 ZIPs

Frost forecast — next 7 nights

live from the National Weather Service

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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 Broomfield, CO

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 2median — 50% chance of a later frost
Safe for tender plantsMay 14only 10% chance of frost after
First fall frostOctober 11median — 10% chance by Sep 26
Growing season160 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 20 and returns around October 21.

From the NOAA station Northglenn, CO, elevation 5,407 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 Broomfield

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 21 – Apr 4
SpinachSow outdoors · Mar 21 – Apr 11
Broccoli, cabbageStart indoors · Feb 21 – Mar 7
Broccoli, cabbageTransplant · Apr 11 – Apr 25
Onion setsPlant outdoors · Apr 4 – Apr 18
PotatoesPlant outdoors · Apr 11 – Apr 25
LettuceSow outdoors · Apr 4 – Apr 18
Carrots, beetsSow outdoors · Apr 11 – Apr 25
TomatoesStart indoors · Mar 7 – Mar 21
TomatoesTransplant · May 9 – May 23
Peppers, eggplantStart indoors · Feb 21 – Mar 7
Peppers, eggplantTransplant · May 16 – May 30
BeansSow outdoors · May 9 – May 23
Sweet cornSow outdoors · May 9 – May 23
Cucumbers, squashSow outdoors · May 9 – May 23
Fall lettuce, spinachSow outdoors · Aug 16 – Aug 30
GarlicPlant cloves · Sep 27 – Nov 1
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 2) and first fall frost (Oct 11) 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 80020 came on Feb 20 — 26 days earlier than the 1991–2020 average (Mar 18).

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 6a in Colorado

563 plants native to the lower 48 states, recorded in Colorado, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. Each links to its USDA PLANTS profile.

Trees 28

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 104

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 251

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 167

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 4

riverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Ftrumpet creeper2 ft · blooms summer · high shade tolerance · to −13 °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 Broomfield, CO.

Soil in Broomfield, CO

The soil mapped at the center of ZIP 80020 is Nunn — clay loam, well drained.

TextureClay loamholds water and nutrients; slow to drain and warm up
pH7.2neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.5%low — add compost
Hydrologic groupCwater soaks in slowly
Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Nunn clay loam, 3 to 5 percent slopes.

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 80020; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Broomfield, CO

Summer high91 °Faverage high, July
Winter low19 °Faverage low, January
Hot days53days a year at 90 °F or more
Freezing nights149nights a year at 32 °F or less
Growing degree days3,168base 50 °F — the season’s usable heat
Longest day15 h 00 mindaylight on June 21
Shortest day9 h 20 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation17.8 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 48 °F, low 19 °F 48°19° JanFebruary: average high 50 °F, low 20 °F 50°20° FebMarch: average high 58 °F, low 28 °F 58°28° MarApril: average high 64 °F, low 35 °F 64°35° AprMay: average high 72 °F, low 44 °F 72°44° MayJune: average high 85 °F, low 53 °F 85°53° JunJuly: average high 91 °F, low 59 °F 91°59° JulAugust: average high 89 °F, low 57 °F 89°57° AugSeptember: average high 82 °F, low 49 °F 82°49° SepOctober: average high 67 °F, low 37 °F 67°37° OctNovember: average high 56 °F, low 27 °F 56°27° NovDecember: average high 48 °F, low 19 °F 48°19° Dec

Precipitation by month inches

0″1″2″3″January: 0.69 in precipitation 0.7 JanFebruary: 0.62 in precipitation 0.6 FebMarch: 1.63 in precipitation 1.6 MarApril: 2.19 in precipitation 2.2 AprMay: 2.53 in precipitation 2.5 MayJune: 2.08 in precipitation 2.1 JunJuly: 2.00 in precipitation 2.0 JulAugust: 1.55 in precipitation 1.6 AugSeptember: 1.82 in precipitation 1.8 SepOctober: 1.24 in precipitation 1.2 OctNovember: 0.83 in precipitation 0.8 NovDecember: 0.62 in precipitation 0.6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Northglenn, CO (4 mi away); precipitation: Broomfield 0.9 Ssw, CO (within 1 mile). Daylight is calculated from latitude.

ZIP codes in Broomfield

800206a
−10 to −5 °F
800216a
−10 to −5 °F
800236a
−10 to −5 °F
800386a
−10 to −5 °F

Colorado planting zones →

Questions about Broomfield

What planting zone is Broomfield, CO?

Broomfield, CO is in USDA hardiness zone 6a on the 2023 map (6a: −10 to −5 °F).

When is the last frost in Broomfield, CO?

The median last spring frost is May 2 and the median first fall frost is October 11 (NOAA 1991–2020 normals, Northglenn station).

When can I plant a garden in Broomfield, CO?

Cool-season crops like peas and spinach go in around Mar 21 – Apr 11; tomatoes, peppers, beans and squash after about May 9, once frost risk has passed.

What kind of onions grow in Broomfield, CO?

Long-day onions: the longest day is 15 h 00 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

How much rain and snow does Broomfield, CO get?

About 17.8 inches of precipitation a year (NOAA 1991–2020 normals).