State guide
Planting zones in Colorado
Colorado spans USDA zones 4a to 7a across its 520 ZIP codes, so there is no single zone for the state and anyone who gives you one is rounding. 39% of its ZIP codes are zone 6a; the rest are not.
Your ZIP code
Get the exact answer for your address
Everything above describes Colorado as a whole. Hardiness zones and freeze dates are published per ZIP code, so yours is exact — enter it and this page will tell you your zone, which NOAA station it comes from and how far away that station is.
Which zone you are in depends where you are
Colorado covers 7 hardiness zones. A guide that gives the state one zone has picked whichever is largest and rounded everyone else into it — which is fine for the 39% in zone 6a and wrong for the other 61%. Here is the actual split, by ZIP code.
| Zone | ZIP codes | Share | |
|---|---|---|---|
| 6a | 201 | 39% | |
| 5b | 199 | 38% | |
| 5a | 70 | 13% | |
| 6b | 31 | 6% | |
| 7a | 12 | 2% | |
| 4b | 6 | 1% | |
| 4a | 1 | 0% |
Zones are published per ZIP code, so yours is exact even though the state's is not. The hardiness tool will tell you which one you are in.
Your freeze dates
Those are the earliest and latest medians among the 210 stations in Colorado with an ordinary freeze window — not an average, and not one station standing in for the rest. Half of years freeze later than a station's own median.
Your growing season
NOAA publishes a growing-season length for each station, and across the 210 stations in Colorado it runs 71–190 days . That figure is published, not computed from the two freeze dates — subtracting one from the other gives the wrong answer wherever a season crosses New Year. Mean summer high (June–August) runs 65–94 °F , reaching the 90 °F point where cool-season crops bolt and tomato and pepper pollen fails — so midsummer sowings of lettuce and its relatives are worth holding in the hotter parts of the state.
The ends of each range, named
A range with no station behind it cannot be checked, and Colorado has too many stations to table them all. So every figure above is reported here with the station standing at each end of it, by name and NOAA ID. No station on this page represents Colorado — these are its edges, which is a different claim.
| Measure | Earliest / lowest | Station | Latest / highest | Station |
|---|---|---|---|---|
| Last spring freeze | April 14 | Grand Junction Wfo, CO USC00053486 | June 21 | Boulder 14 W, CO USW00094075 |
| First fall freeze | September 2 | Boulder 14 W, CO USW00094075 | October 26 | Palisade, CO USC00056266 |
| Growing season | 71 days | Boulder 14 W, CO USW00094075 | 190 days | Palisade, CO USC00056266 |
| Mean summer high | 65 °F | Boulder 14 W, CO USW00094075 | 94 °F | Uravan, CO USC00058560 |
These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.
When to start seeds in Colorado
Every spring job for 63 crop dates, counted from this state's own last spring freeze. Each is a range across all 210 stations — the earliest and latest that job falls anywhere in Colorado — because no one station speaks for a whole state. The ranges are wide on purpose: that width is the state.
| Crop | Job | When | Offset |
|---|---|---|---|
| Green Onions | Start indoors | February 17 – April 26 | 8 weeks before |
| Peppers | Start indoors | February 17 – April 26 | 8 weeks before |
| Broccoli | Start indoors | March 3 – May 10 | 6 weeks before |
| Cabbage | Start indoors | March 3 – May 10 | 6 weeks before |
| Collards | Start indoors | March 3 – May 10 | 6 weeks before |
| Kale | Start indoors | March 3 – May 10 | 6 weeks before |
| Leaf Lettuce | Start indoors | March 3 – May 10 | 6 weeks before |
| Peas | Direct sow | March 3 – May 10 | 6 weeks before |
| Spinach | Direct sow | March 3 – May 10 | 6 weeks before |
| Sweet Potato | Start indoors | March 3 – May 10 | 6 weeks before |
| Tomatoes | Start indoors | March 3 – May 10 | 6 weeks before |
| Bok Choy | Start indoors | March 10 – May 17 | 5 weeks before |
| Kohlrabi | Start indoors | March 10 – May 17 | 5 weeks before |
| Swiss Chard | Start indoors | March 10 – May 17 | 5 weeks before |
| Arugula | Direct sow | March 17 – May 24 | 4 weeks before |
| Baby Salad Greens | Direct sow | March 17 – May 24 | 4 weeks before |
| Beets | Direct sow | March 17 – May 24 | 4 weeks before |
| Green Onions | Direct sow | March 17 – May 24 | 4 weeks before |
| Mustard Greens | Direct sow | March 17 – May 24 | 4 weeks before |
| Okra | Start indoors | March 17 – May 24 | 4 weeks before |
| Radishes | Direct sow | March 17 – May 24 | 4 weeks before |
| Turnips | Direct sow | March 17 – May 24 | 4 weeks before |
| Cabbage | Set out | March 24 – May 31 | 3 weeks before |
| Carrots | Direct sow | March 24 – May 31 | 3 weeks before |
| Collards | Direct sow | March 24 – May 31 | 3 weeks before |
| Collards | Set out | March 24 – May 31 | 3 weeks before |
| Cucumbers | Start indoors | March 24 – May 31 | 3 weeks before |
| Green Onions | Set out | March 24 – May 31 | 3 weeks before |
| Kale | Direct sow | March 24 – May 31 | 3 weeks before |
| Kale | Set out | March 24 – May 31 | 3 weeks before |
| Kohlrabi | Direct sow | March 24 – May 31 | 3 weeks before |
| Kohlrabi | Set out | March 24 – May 31 | 3 weeks before |
| Leaf Lettuce | Direct sow | March 24 – May 31 | 3 weeks before |
| Pumpkins | Start indoors | March 24 – May 31 | 3 weeks before |
| Summer Squash | Start indoors | March 24 – May 31 | 3 weeks before |
| Winter Squash | Start indoors | March 24 – May 31 | 3 weeks before |
| Zucchini | Start indoors | March 24 – May 31 | 3 weeks before |
| Bok Choy | Direct sow | March 31 – June 7 | 2 weeks before |
| Bok Choy | Set out | March 31 – June 7 | 2 weeks before |
| Broccoli | Set out | March 31 – June 7 | 2 weeks before |
| Cilantro | Direct sow | March 31 – June 7 | 2 weeks before |
| Leaf Lettuce | Set out | March 31 – June 7 | 2 weeks before |
| Swiss Chard | Direct sow | March 31 – June 7 | 2 weeks before |
| Swiss Chard | Set out | March 31 – June 7 | 2 weeks before |
| Dill | Direct sow | April 7 – June 14 | 1 week before |
| Bush Beans | Direct sow | April 21 – June 28 | 1 week after |
| Cucumbers | Set out | April 21 – June 28 | 1 week after |
| Pumpkins | Direct sow | April 21 – June 28 | 1 week after |
| Pumpkins | Set out | April 21 – June 28 | 1 week after |
| Summer Squash | Direct sow | April 21 – June 28 | 1 week after |
| Summer Squash | Set out | April 21 – June 28 | 1 week after |
| Sweet Corn | Direct sow | April 21 – June 28 | 1 week after |
| Tomatoes | Set out | April 21 – June 28 | 1 week after |
| Winter Squash | Direct sow | April 21 – June 28 | 1 week after |
| Winter Squash | Set out | April 21 – June 28 | 1 week after |
| Zucchini | Direct sow | April 21 – June 28 | 1 week after |
| Zucchini | Set out | April 21 – June 28 | 1 week after |
| Cucumbers | Direct sow | April 28 – July 5 | 2 weeks after |
| Okra | Direct sow | April 28 – July 5 | 2 weeks after |
| Okra | Set out | April 28 – July 5 | 2 weeks after |
| Peppers | Set out | April 28 – July 5 | 2 weeks after |
| Southern Peas | Direct sow | April 28 – July 5 | 2 weeks after |
| Sweet Potato | Set out | April 28 – July 5 | 2 weeks after |
The week offsets are conventional extension guidance and vary by variety; the freeze dates they are counted from are measured. For a single date rather than a range, run when do I start my seeds? with your own ZIP code.
What survives the winter changes across Colorado
Of 74 perennial fruits, nuts, berries, vegetables and herbs, 58 come through the winter in zone 7a and only 34 in zone 4a. Winter hardiness runs on the zone alone, so each row below is exact for the ZIP codes in it.
| Zone | ZIPs | Survive | Fail for being too warm |
|---|---|---|---|
| 4a | 1 | 34 of 74 | 0 |
| 4b | 6 | 34 of 74 | 0 |
| 5a | 70 | 48 of 74 | 0 |
| 5b | 199 | 48 of 74 | 0 |
| 6a | 201 | 51 of 74 | 0 |
| 6b | 31 | 51 of 74 | 0 |
| 7a | 12 | 58 of 74 | 1 |
The last column is the counterintuitive one. Most temperate fruit needs a documented number of hours below about 45 °F to break dormancy and set a crop, so an apple fails in a winter that is too warm; currants and rhubarb cook in the summer heat that comes with it. See the full list with reasons.
Your own ZIP
Work out your own dates
Each of these takes a ZIP code and answers for that ZIP alone, citing the station it used and how far away it is. There is a ZIP box in the header of every page.
- What survives my winter?
Runs on the hardiness zone, so it answers exactly for your ZIP code rather than for Colorado as a whole — 74 perennial fruits, berries, vegetables and herbs.
- When do I start my seeds?
Dates every spring job from your own last freeze — sow indoors, set out, direct sow.
- When do I sow the next round?
How often each crop is worth re-sowing, and when the next sowing is due.
- What can I still plant?
Counts the growing days left before your first fall freeze, crop by crop.
Metro areas in Colorado
7 metro areas here have its own page, with the freeze dates from every station serving it, a spring calendar built from those stations, and every ZIP code in it listed with that ZIP code's exact zone and nearest station.
- Denver-Aurora-Centennial, CO Zones 4a, 5a, 5b, 6a
- Colorado Springs, CO Zones 5a–6a
- Greeley, CO Zones 5a–5b
- Fort Collins-Loveland, CO Zones 5a–5b
- Boulder, CO Zones 5b–6a
- Grand Junction, CO Zones 5b–7a
- Pueblo, CO Zone 6a
Counties in Colorado
20 countys here have its own page, listing every ZIP code in it with that ZIP code's exact zone and nearest station. These are the smaller places outside the metro areas above — where most of Colorado's ZIP codes actually are.
- Eagle County, CO Zones 5a–6a
- Gunnison County, CO Zones 4b–6a
- Fremont County, CO Zones 5b–6a
- Las Animas County, CO Zone 6a
- Routt County, CO Zones 5a–5b
- Grand County, CO Zones 5a–5b
- Logan County, CO Zone 5b
- Montrose County, CO Zones 6a–6b
- Lincoln County, CO Zone 5b
- Montezuma County, CO Zones 6a–7a
- Yuma County, CO Zones 5b–6a
- Baca County, CO Zone 6b
- Garfield County, CO Zones 5b–6b
- Kit Carson County, CO Zones 5b–6a
- Morgan County, CO Zones 5a–5b
- Saguache County, CO Zones 5a–5b
- Washington County, CO Zone 5b
- La Plata County, CO Zones 6a–6b
- Moffat County, CO Zones 5a–6a
- Otero County, CO Zone 6a
Other states to compare
Gear
If you want to act on this
Each link opens an Amazon search rather than a product we picked. We have not tested these and do not rank them — the search is the honest version, and you choose.
- Trunk wrapZone 4a is cold enough that winter sun on a young trunk does more damage than the cold does.
- Row cover and frost clothThe season here closes at the first fall freeze dated above — a cover buys back some of those days at the end.
- MulchFor the perennials nearest their cold limit in zone 4a, where an insulated crown is what decides whether they come back.
As an Amazon Associate we earn from qualifying purchases. That costs you nothing extra, and it buys no influence over anything on this site: the dates come from NOAA normals and the zones from the USDA, and no product affects either.
Sources
Where these numbers come from
The hardiness zone is the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. The freeze dates, growing seasons and summer highs are NOAA's 1991–2020 Climate Normals, read from every station in Colorado. Which ZIP codes are in Colorado comes from the Census ZIP-to-county relation, since a county's federal code begins with its state's. Nothing here is estimated.
This page names no single station for Colorado on purpose. Picking one to represent a state sounds reasonable and is not — the same reason the metro pages refuse it, only more so at this size. Instead every range names the station at each end, so you can check both without either one being made to speak for the state.