Jefferson, CO frost dates
Last spring frostJun 15median date
First fall frostSep 9median date
Growing season86 daysfrost-free
Hardiness zone5aZone 5a
How Jefferson compares
- In 8 years out of 10, the last spring frost in Jefferson falls between June 1 and June 30, a 29-day window. The first fall frost falls between August 26 and September 22.
- The median last frost is 35 days later than the Colorado median of May 11.
- Its 86-day growing season is longer than 6% of the 374 Colorado places with a regular frost season (state median 146 days).
- The last frost is 43 days later than the zone 5a median of May 3. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 5a chart.
- The weather station records an average of 236 nights a year at or below 32°F.
- Compared with Castle Rock, CO, 71 km away, the last frost here is 37 days later than there and the growing season is 60 days shorter.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | June 1 |
| 50% (median) | June 15 |
| 10% (safe for tender plants) | June 30 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | August 26 |
| 50% (median) | September 9 |
| 90% (late) | September 22 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Jefferson, CO
Jefferson, CO frost dates — last frost Jun 15, first frost Sep 9, zone 5a. whenisthelastfrost.com
Crop
JFMAMJJASOND
Start indoors: Mar 23 to Apr 6Transplant outside: May 18 to Jun 1
Start indoors: Apr 6 to Apr 20Transplant outside: Jun 29 to Jul 13
Start indoors: Apr 6 to Apr 20Transplant outside: Jun 29 to Jul 13
Start indoors: Apr 20 to May 4Transplant outside: Jun 22 to Jul 6
Start indoors: Apr 20 to May 4Transplant outside: May 25 to Jun 8Sow outdoors: May 18 to Jun 22Plant for fall: Jul 15 to Aug 12
Start indoors: Apr 20 to May 4Transplant outside: May 18 to Jun 1Sow outdoors: May 18 to Jun 1Plant for fall: Jul 1 to Jul 22
Start indoors: Apr 20 to May 4Transplant outside: Jun 1 to Jun 15
Start indoors: Apr 20 to May 4Transplant outside: May 25 to Jun 8
Start indoors: Apr 20 to May 4Transplant outside: Jun 1 to Jun 15
Start indoors: May 4 to May 18Transplant outside: Jul 6 to Jul 20Sow outdoors: Jul 6 to Jul 20
Start indoors: May 4 to May 18Transplant outside: Jun 22 to Jul 6
Sow outdoors: May 4 to May 25
Sow outdoors: May 4 to May 25Plant for fall: Jul 15 to Aug 5
Sow outdoors: May 11 to Jun 22Plant for fall: Jul 29 to Aug 19
Start indoors: May 18 to May 25Transplant outside: Jun 29 to Jul 6Sow outdoors: Jun 22 to Jul 6
Start indoors: May 18 to May 25Sow outdoors: Jun 22 to Jul 6
Start indoors: May 18 to May 25Sow outdoors: Jun 22 to Jul 6
Start indoors: May 18 to May 25Transplant outside: Jun 29 to Jul 13
Sow outdoors: May 25 to Jun 22
Sow outdoors: May 25 to Jun 22
Sow outdoors: May 25 to Jun 15
Sow outdoors: Jun 1 to Jun 29
Sow outdoors: Jun 1 to Jun 22Plant for fall: Jul 15 to Aug 5
Sow outdoors: Jun 22 to Jul 13
Sow outdoors: Jun 22 to Jul 6
Transplant outside: Jun 29 to Jul 20
Plant for fall: Aug 26 to Sep 30
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Jefferson, CO
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Mar 23 – Apr 6 | May 18 – Jun 1 | — | — |
| Peppers Warning: Your frost-free season is about 86 days, which is tight for peppers (75+ days). Choose early varieties and use transplants or row covers. | Apr 6 – Apr 20 | Jun 29 – Jul 13 | — | — |
| Eggplant Warning: Your frost-free season is about 86 days, which is tight for eggplant (75+ days). Choose early varieties and use transplants or row covers. | Apr 6 – Apr 20 | Jun 29 – Jul 13 | — | — |
| Tomatoes | Apr 20 – May 4 | Jun 22 – Jul 6 | — | — |
| Lettuce | Apr 20 – May 4 | May 25 – Jun 8 | May 18 – Jun 22 | Jul 15 – Aug 12 |
| Kale | Apr 20 – May 4 | May 18 – Jun 1 | May 18 – Jun 1 | Jul 1 – Jul 22 |
| Broccoli | Apr 20 – May 4 | Jun 1 – Jun 15 | — | — |
| Cabbage | Apr 20 – May 4 | May 25 – Jun 8 | — | — |
| Cauliflower | Apr 20 – May 4 | Jun 1 – Jun 15 | — | — |
| Okra | May 4 – May 18 | Jul 6 – Jul 20 | Jul 6 – Jul 20 | — |
| Basil | May 4 – May 18 | Jun 22 – Jul 6 | — | — |
| Peas | — | — | May 4 – May 25 | — |
| Spinach | — | — | May 4 – May 25 | Jul 15 – Aug 5 |
| Radishes | — | — | May 11 – Jun 22 | Jul 29 – Aug 19 |
| Cucumbers | May 18 – May 25 | Jun 29 – Jul 6 | Jun 22 – Jul 6 | — |
| Zucchini & Summer Squash | May 18 – May 25 | — | Jun 22 – Jul 6 | — |
| Winter Squash & Pumpkins Warning: Your frost-free season is about 86 days, which is tight for winter squash & pumpkins (100+ days). Choose early varieties and use transplants or row covers. | May 18 – May 25 | — | Jun 22 – Jul 6 | — |
| Melons & Watermelon Warning: Your frost-free season is about 86 days, which is tight for melons & watermelon (85+ days). Choose early varieties and use transplants or row covers. | May 18 – May 25 | Jun 29 – Jul 13 | — | — |
| Carrots | — | — | May 25 – Jun 22 | — |
| Beets | — | — | May 25 – Jun 22 | — |
| Potatoes | — | — | May 25 – Jun 15 | — |
| Swiss Chard | — | — | Jun 1 – Jun 29 | — |
| Cilantro | — | — | Jun 1 – Jun 22 | Jul 15 – Aug 5 |
| Green Beans | — | — | Jun 22 – Jul 13 | — |
| Sweet Corn Warning: Your frost-free season is about 86 days, which is tight for sweet corn (80+ days). Choose early varieties and use transplants or row covers. | — | — | Jun 22 – Jul 6 | — |
| Sweet Potatoes Warning: Your frost-free season is about 86 days, which is tight for sweet potatoes (100+ days). Choose early varieties and use transplants or row covers. | — | Jun 29 – Jul 20 | — | — |
| Garlic | — | — | — | Aug 26 – Sep 30 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Grant, CO weather station, 21 km away (elevation 8,675 ft (2,644 m)).
Frost dates near Jefferson
- Como Jun 16 · Sep 9
- Shawnee Jun 16 · Sep 8
- Grant Jun 15 · Sep 9
- Bailey Jun 16 · Sep 8
- Fairplay Jun 16 · Sep 9
- Alma Jun 16 · Sep 9
- Pine Jun 16 · Sep 8
- Lake George Jun 2 · Sep 19
- Breckenridge frost any month
- Buffalo Creek May 16 · Sep 29
Frequently asked questions
When is the last frost in Jefferson, CO?
The median last spring frost in Jefferson, CO is June 15. There is still about a 10% chance of frost after June 30, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Jefferson, CO?
The median first fall frost is September 9, with about a 10% chance of frost before August 26.
How long is the growing season in Jefferson, CO?
About 86 days between the median last spring frost and first fall frost.
What planting zone is Jefferson, CO?
Jefferson, CO is in USDA hardiness zone 5a.