Gardening in Denver-Aurora-Centennial, CO
This metro spans USDA zones 4a to 6a, so there is no single zone for Denver-Aurora-Centennial, CO and anyone who gives you one is rounding. 61% of its ZIP codes are zone 6a; the rest are not.
Which zone you are in depends where you are
Denver-Aurora-Centennial, CO covers 4 hardiness zones. A guide that gives the metro one zone has picked whichever is largest and rounded everyone else into it — which is fine for the 61% in zone 6a and wrong for the other 39%. Here is the actual split.
| Zone | ZIP codes | Share | |
|---|---|---|---|
| 6a | 81 | 61% | |
| 5b | 45 | 34% | |
| 5a | 6 | 5% | |
| 4a | 1 | 1% |
Zones are published per ZIP code, so yours is exact even though the metro'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 33 stations serving this metro — not an average, and not one station standing in for the rest. Half of years freeze later than a station's own median.
The spread is the point. Even in a metro that is one hardiness zone throughout, its stations disagree about the last spring freeze. Hardiness zone and frost date measure different things — a zone is the average annual coldest night, a freeze date is when the season turns — and a place can be uniform in one and varied in the other. Use the tools below with your own ZIP rather than the ends of this range.
Your growing season
NOAA publishes a growing-season length for each station, and across the 33 stations serving Denver-Aurora-Centennial, CO it runs 71–165 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 65–89 °F , below the 90 °F point where cool-season crops reliably bolt.
When to start seeds in Denver-Aurora-Centennial, CO
Every spring job for 63 crop dates, counted from this metro's own last spring freeze. Each is a range across all 33 stations — the earliest and latest that job falls anywhere in the metro — because no one station speaks for the whole area.
| Crop | Job | When | Offset |
|---|---|---|---|
| Green Onions | Start indoors | March 5 – April 26 | 8 weeks before |
| Peppers | Start indoors | March 5 – April 26 | 8 weeks before |
| Broccoli | Start indoors | March 19 – May 10 | 6 weeks before |
| Cabbage | Start indoors | March 19 – May 10 | 6 weeks before |
| Collards | Start indoors | March 19 – May 10 | 6 weeks before |
| Kale | Start indoors | March 19 – May 10 | 6 weeks before |
| Leaf Lettuce | Start indoors | March 19 – May 10 | 6 weeks before |
| Peas | Direct sow | March 19 – May 10 | 6 weeks before |
| Spinach | Direct sow | March 19 – May 10 | 6 weeks before |
| Sweet Potato | Start indoors | March 19 – May 10 | 6 weeks before |
| Tomatoes | Start indoors | March 19 – May 10 | 6 weeks before |
| Bok Choy | Start indoors | March 26 – May 17 | 5 weeks before |
| Kohlrabi | Start indoors | March 26 – May 17 | 5 weeks before |
| Swiss Chard | Start indoors | March 26 – May 17 | 5 weeks before |
| Arugula | Direct sow | April 2 – May 24 | 4 weeks before |
| Baby Salad Greens | Direct sow | April 2 – May 24 | 4 weeks before |
| Beets | Direct sow | April 2 – May 24 | 4 weeks before |
| Green Onions | Direct sow | April 2 – May 24 | 4 weeks before |
| Mustard Greens | Direct sow | April 2 – May 24 | 4 weeks before |
| Okra | Start indoors | April 2 – May 24 | 4 weeks before |
| Radishes | Direct sow | April 2 – May 24 | 4 weeks before |
| Turnips | Direct sow | April 2 – May 24 | 4 weeks before |
| Cabbage | Set out | April 9 – May 31 | 3 weeks before |
| Carrots | Direct sow | April 9 – May 31 | 3 weeks before |
| Collards | Direct sow | April 9 – May 31 | 3 weeks before |
| Collards | Set out | April 9 – May 31 | 3 weeks before |
| Cucumbers | Start indoors | April 9 – May 31 | 3 weeks before |
| Green Onions | Set out | April 9 – May 31 | 3 weeks before |
| Kale | Direct sow | April 9 – May 31 | 3 weeks before |
| Kale | Set out | April 9 – May 31 | 3 weeks before |
| Kohlrabi | Direct sow | April 9 – May 31 | 3 weeks before |
| Kohlrabi | Set out | April 9 – May 31 | 3 weeks before |
| Leaf Lettuce | Direct sow | April 9 – May 31 | 3 weeks before |
| Pumpkins | Start indoors | April 9 – May 31 | 3 weeks before |
| Summer Squash | Start indoors | April 9 – May 31 | 3 weeks before |
| Winter Squash | Start indoors | April 9 – May 31 | 3 weeks before |
| Zucchini | Start indoors | April 9 – May 31 | 3 weeks before |
| Bok Choy | Direct sow | April 16 – June 7 | 2 weeks before |
| Bok Choy | Set out | April 16 – June 7 | 2 weeks before |
| Broccoli | Set out | April 16 – June 7 | 2 weeks before |
| Cilantro | Direct sow | April 16 – June 7 | 2 weeks before |
| Leaf Lettuce | Set out | April 16 – June 7 | 2 weeks before |
| Swiss Chard | Direct sow | April 16 – June 7 | 2 weeks before |
| Swiss Chard | Set out | April 16 – June 7 | 2 weeks before |
| Dill | Direct sow | April 23 – June 14 | 1 week before |
| Bush Beans | Direct sow | May 7 – June 28 | 1 week after |
| Cucumbers | Set out | May 7 – June 28 | 1 week after |
| Pumpkins | Direct sow | May 7 – June 28 | 1 week after |
| Pumpkins | Set out | May 7 – June 28 | 1 week after |
| Summer Squash | Direct sow | May 7 – June 28 | 1 week after |
| Summer Squash | Set out | May 7 – June 28 | 1 week after |
| Sweet Corn | Direct sow | May 7 – June 28 | 1 week after |
| Tomatoes | Set out | May 7 – June 28 | 1 week after |
| Winter Squash | Direct sow | May 7 – June 28 | 1 week after |
| Winter Squash | Set out | May 7 – June 28 | 1 week after |
| Zucchini | Direct sow | May 7 – June 28 | 1 week after |
| Zucchini | Set out | May 7 – June 28 | 1 week after |
| Cucumbers | Direct sow | May 14 – July 5 | 2 weeks after |
| Okra | Direct sow | May 14 – July 5 | 2 weeks after |
| Okra | Set out | May 14 – July 5 | 2 weeks after |
| Peppers | Set out | May 14 – July 5 | 2 weeks after |
| Southern Peas | Direct sow | May 14 – July 5 | 2 weeks after |
| Sweet Potato | Set out | May 14 – 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 Denver-Aurora-Centennial, CO
Of 74 perennial fruits, nuts, berries, vegetables and herbs, 51 come through the winter in zone 6a and only 34 in zone 4a. That is a different garden at each end of the same metro.
| Zone | ZIPs | Survive | Fail for being too warm |
|---|---|---|---|
| 4a | 1 | 34 of 74 | 0 |
| 5a | 6 | 48 of 74 | 0 |
| 5b | 45 | 48 of 74 | 0 |
| 6a | 81 | 51 of 74 | 0 |
The last column is the counterintuitive one, and it is why the totals do not simply rise as the winters get milder. 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.
The 33 stations behind these numbers
Every figure above comes from these, and each is named so you can check it. Distances vary by ZIP code, so the tools report yours rather than this page guessing.
| Station | NOAA ID | Last spring freeze | First fall freeze | Season |
|---|---|---|---|---|
| Bailey, CO | USC00050454 | June 16 | September 8 | 84 days |
| Boulder 14 W, CO | USW00094075 | June 21 | September 2 | 71 days |
| Brighton 3 SE, CO | USC00050950 | May 3 | October 7 | 155 days |
| Byers 5 Ene, CO | USC00051179 | May 13 | October 2 | 142 days |
| Cabin Creek, CO | USC00051186 | June 6 | September 19 | 103 days |
| Castle Rock, CO | USC00051401 | May 9 | October 2 | 143 days |
| Cheesman, CO | USC00051528 | May 17 | October 1 | 135 days |
| Cherry Creek Dam, CO | USC00051547 | May 7 | October 8 | 152 days |
| Coal Creek Canyon, CO | USC00051681 | June 5 | September 16 | 103 days |
| Denver Centennial AP, CO | USW00093067 | May 5 | October 8 | 154 days |
| Denver INTL AP, CO | USW00003017 | May 5 | October 9 | 156 days |
| Denver Water Dept, CO | USC00052223 | April 30 | October 12 | 165 days |
| Denver-Stapleton, CO | USW00023062 | May 4 | October 8 | 156 days |
| Eastonville 2 Nnw, CO | USC00052494 | May 29 | September 21 | 114 days |
| Elizabeth 2Nw, CO | USC00052631 | May 16 | October 2 | 137 days |
| Evergreen, CO | USC00052790 | May 23 | September 22 | 118 days |
| Fairplay S Park Rd, CO | USC00052816 | June 16 | September 9 | 83 days |
| Georgetown, CO | USC00053261 | May 30 | September 19 | 112 days |
| Grant, CO | USC00053530 | June 15 | September 9 | 84 days |
| Karval, CO | USC00054444 | May 9 | October 6 | 149 days |
| Kassler, CO | USC00054452 | May 8 | October 3 | 147 days |
| Lake George 8 SW, CO | USC00054742 | June 2 | September 19 | 108 days |
| Lakewood, CO | USC00054762 | May 3 | October 7 | 155 days |
| Limon Wsmo, CO | USW00093010 | May 21 | September 26 | 127 days |
| Marston Fltr Plt, CO | USC00055402 | May 2 | October 11 | 160 days |
| Matheson 8 SE, CO | USC00055427 | May 12 | October 2 | 141 days |
| Monument, CO | USC00055734 | May 14 | October 1 | 138 days |
| Northglenn, CO | USC00055984 | May 2 | October 11 | 160 days |
| Parker, CO | USC00056323 | May 9 | October 3 | 145 days |
| Ralston Rsvr, CO | USC00056816 | May 3 | October 14 | 161 days |
| Roxborough SP, CO | USC00057249 | May 16 | October 1 | 136 days |
| Strontia Springs Dam, CO | USC00058022 | May 16 | September 29 | 132 days |
| Wheat Ridge 2, CO | USC00058995 | May 5 | October 5 | 151 days |
These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.
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 for all of Denver-Aurora-Centennial, CO at once — zone across 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.
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 are NOAA's 1991–2020 Climate Normals, read from every station whose normals cover a ZIP code in this metro. Nothing here is estimated, and no station stands in for another.
This page names no single station on purpose. Picking one to represent a metro sounds reasonable and is not: the station serving the most ZIP codes is an artifact of where ZIP centroids happen to fall, and it selects a lock on the Monongahela for Pittsburgh and a far southern suburb for Chicago. A range across every station is true; a single cited date for a whole metro is not.