What does USDA hardiness zone 6b mean in Colorado?

Zone 6b means an average annual extreme minimum winter temperature of −5 to 0 °F — the standard USDA measure of which perennials survive winter. 19 locations in Colorado fall in this zone. It does not set planting dates; see the frost calendar below for that.

Where in Colorado's zone 6b is the growing season longest?

Palisade runs the longest season on this page at about 190 days; Dove Creek is shortest at about 113 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.

When should I plant tomatoes in Colorado's zone 6b?

Using Olathe's frost dates (this page's median-season location): start seeds indoors about Mar 7 – Mar 21, then transplant outside about May 9 – May 16. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.

Does every location in Colorado's zone 6b have the same frost dates?

No — they do not all share a weather station, so frost dates vary by a week or more across the 19 locations listed (see the table above for each location's own dates).

USDA zone 6b in Colorado

−5 to 0 °F avg. annual extreme minimum · 19 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 6b covers 19 locations across Colorado (average annual extreme minimum −5 to 0 °F): Arboles, CO, Delta, CO, Dove Creek, CO, Dove Creek, CO, Durango, CO, Fruita, CO, and 13 more. Average last spring frost across this group ranges April 17 (Palisade) to June 3 (Dove Creek), and growing seasons run 113–190 days (Dove Creek to Palisade) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Colorado location's own frost dates; the printable planting calendar uses Olathe, this group's median-season location.

USDA zone: 6b−5 to 0 °F
Last frost range: Apr 17–Jun 3avg, 32°F
First frost range: Sep 25–Oct 26avg, 32°F
Growing season range: 113–190days

Locations in this group

Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.

Own frost dates per location.
Location	Also covers	Nearest station	Last frost	First frost	Season (days)
Arboles	—	Ignacio 6ese	May 23	Sep 29	128
Delta	—	Delta 3e	May 1	Oct 7	159
Dove Creek	—	Northdale	Jun 3	Sep 25	113
Dove Creek	—	Cedar Pt	May 16	Oct 11	145
Durango	Navajo Dam	Durango La Plata Co Ap	Jun 1	Sep 27	116
Fruita	—	Grand Junction Walker Fld	Apr 28	Oct 16	171
Hotchkiss	Paonia	Paonia 1sw	May 3	Oct 12	159
Lewis	Dove Creek	Yellow Jacket 2w	May 17	Oct 9	145
Lewis	—	Hovenweep Nm	May 2	Oct 10	159
Loma	—	Colorado Nm	Apr 26	Oct 16	172
Loma	—	Altenbern	May 25	Sep 25	120
Montrose	—	Montrose #2	Apr 28	Oct 14	167
Naturita	—	Norwood	May 25	Oct 1	128
Olathe *	—	Montrose Rgnl Ap	May 2	Oct 8	157
Orchard	Cedaredge	Cedaredge 3e	May 3	Oct 9	156
Palisade	—	Palisade	Apr 17	Oct 26	190
Redlands	—	Glade Park 17w	May 21	Sep 26	126
Springfield	—	Springfield Comanche	May 3	Oct 10	158
Walsh	Two Buttes, Vilas	Walsh 1 W	Apr 30	Oct 14	166

* Olathe is this group's median-season location — the calendar below is computed from its data.

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.

Planting calendar (Olathe, representative)

Computed from Olathe's average frost dates — the median-season location in this Coloradozone 6b group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).

Crop

JanFebMarAprMayJunJulAugSepOctNovDec

Tomato

Pepper

Cucumber

Summer squash / zucchini

Start indoors
Plant out
Fall sowing
First harvest

Planting windows for Olathe (Colorado, zone 6b), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 7 – Mar 21	May 9 – May 16	Jul 8 – Jul 28	—	matures comfortably
Pepper	Very tender	Feb 21 – Mar 7	May 16 – May 23	Jul 15 – Aug 14	—	matures comfortably
Cucumber	Tender	Apr 4 – Apr 11	May 9 – May 16	Jun 28 – Jul 18	—	matures comfortably
Summer squash / zucchini	Tender	—	May 9 – May 16	Jun 23 – Jul 8	—	matures comfortably
Bush bean	Tender	—	May 9 – May 16	Jun 28 – Jul 8	Aug 9 – Aug 19	matures comfortably
Sweet corn	Tender	—	May 2 – May 16	Jul 1 – Jul 31	—	matures comfortably
Basil	Very tender	Mar 21 – Apr 4	May 9 – May 16	Jun 8 – Jun 23	—	matures comfortably
Lettuce	Half-hardy	Mar 21 – Apr 4	Apr 4 – Apr 18	May 19 – Jun 3	Jul 26 – Aug 10	matures comfortably
Pea	Hardy	—	Mar 21 – Apr 4	May 15 – May 30	Jul 16 – Jul 31	matures comfortably
Spinach	Hardy	—	Mar 21 – Apr 4	Apr 30 – May 10	Aug 5 – Aug 15	matures comfortably
Carrot	Half-hardy	—	Apr 11 – Apr 18	Jun 10 – Jun 30	Jul 6 – Jul 26	matures comfortably
Broccoli	Half-hardy	Mar 7 – Mar 21	Apr 4 – Apr 18	May 29 – Jun 18	Jul 11 – Jul 31	matures comfortably

Which crops fit this growing season

Using Olathe's own 157-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.

Frost & freeze dates (Olathe)

From NOAA's 1991–2020 Climate Normals at station USW00093013. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.

Freeze probabilities by temperature threshold (MM/DD, NOAA 1991–2020), Olathe.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	May 17	Jun 1	Sep 30	Oct 11	134
32°F (freeze)	May 2	May 17	Oct 8	Oct 22	157
28°F	Apr 19	May 5	Oct 20	Nov 2	181
24°F	Apr 5	Apr 22	Oct 30	Nov 13	206

Growing degree days

Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 19 locations is 2,862; Olathe's own reading is shown below.

Annual growing degree days for Olathe (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	2,862	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	5,022	cool-season crops (brassicas, greens)

Hardiness zone 6b in Colorado

Zone 6b means an average annual extreme minimum winter temperature of about −5 to 0 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Colorado spans 7 hardiness zones in this dataset — see all Colorado locations for the full range, including zones4a, 4b, 5a, 5b, 6a, 7a.

Explore zone 6b in other states at zone 6b, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 6b mean in Colorado?: Zone 6b means an average annual extreme minimum winter temperature of −5 to 0 °F — the standard USDA measure of which perennials survive winter. 19 locations in Colorado fall in this zone. It does not set planting dates; see the frost calendar below for that.
Where in Colorado's zone 6b is the growing season longest?: Palisade runs the longest season on this page at about 190 days; Dove Creek is shortest at about 113 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
When should I plant tomatoes in Colorado's zone 6b?: Using Olathe's frost dates (this page's median-season location): start seeds indoors about Mar 7 – Mar 21, then transplant outside about May 9 – May 16. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
Does every location in Colorado's zone 6b have the same frost dates?: No — they do not all share a weather station, so frost dates vary by a week or more across the 19 locations listed (see the table above for each location's own dates).

Sources & method

Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.