Frost dates for Boulder, CO
When the last spring frost and first fall frost usually come, and when to plant, from 30 years of NOAA weather records.
Last spring frost
May 6
typical year
Safe to plant
May 18
frost is over in 9 of 10 years
First fall frost
October 5
typical year
Growing season
151 days
frost-free, typical year
Frost watch this week
Tonight's and the next six nights' lows from the National Weather Service forecast for the station's location. Frost: 32°F or colder. Possible frost: 33–36°F, mostly in low spots on clear, still nights.
When to plant
Counted from this page's frost dates. Warm-season crops wait for the safe-to-plant date.
| Crop | Start indoors | Plant outside | Fall planting |
|---|---|---|---|
| Cool-season crops | |||
| Peas | – | Apr 8 – 22 | – |
| Spinach | – | Mar 25 – Apr 15 | Aug 10 – 24 |
| Lettuce | – | Apr 8 – 29 | Aug 10 – 24 |
| Radishes | – | Apr 8 – May 20 | Aug 24 – Sep 7 |
| Onions | – | Apr 8 – 22 | – |
| Potatoes | – | Apr 15 – 29 | – |
| Carrots | – | Apr 15 – May 6 | Jul 13 – 27 |
| Beets | – | Apr 8 – 22 | Jul 27 – Aug 10 |
| Kale | Feb 25 – Mar 11 | Apr 8 – 22 | Jul 27 – Aug 10 |
| Broccoli | Feb 25 – Mar 11 | Apr 22 – May 6 | Jul 27 – Aug 10 |
| Cabbage | Feb 11 – 25 | Apr 8 – 22 | Jul 27 – Aug 10 |
| Garlic | – | – | Aug 24 – Sep 14 |
| Warm-season crops | |||
| Tomatoes | Mar 23 – Apr 6 | May 18 – Jun 1 | – |
| Peppers | Mar 16 – 30 | May 25 – Jun 8 | – |
| Cucumbers | – | May 18 – Jun 8 | – |
| Zucchini | – | May 18 – Jun 15 | – |
| Pumpkins | – | May 18 – Jun 8 | – |
| Green beans | – | May 18 – Jul 27 | – |
| Sweet corn | – | May 18 – Jun 15 | – |
| Basil | Apr 13 – 27 | May 25 – Jun 1 | – |
Onions: from sets. Green beans: until 10 weeks before the first fall frost. Garlic: harvest next summer.
The year at a glance
Start indoors Plant outside Fall planting
The chance of frost, by date
| 1 year in 10 | Half of years | 9 years in 10 | |
|---|---|---|---|
| Spring frost after | May 18 | May 6 | April 24 |
| Fall frost before | September 21 | October 5 | October 18 |
Frost here means 32°F or colder. Read across: in 1 year in 10, spring frost carries on past the first date, which is why that date is the safe-to-plant date.
Hard freeze (28°F)
A hard freeze kills most garden plants, even hardy ones. The last one in spring usually comes around April 27 (May 10 in a late year), and the first one in fall around October 15.
Towns that use these dates
This is the nearest NOAA station with frost records for 3 towns.
Boulder, Louisville, Superior
Where these dates come from
NOAA weather station BOULDER, CO US (USC00050848), 1991–2020 climate normals. It's the nearest station for 8 zip codes, all within 9 miles:
80026, 80027, 80301, 80302, 80303, 80304, 80305, 80310
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.