Frost Dates for Castle Rock, CO
In Castle Rock, CO, the average last spring frost is around May 9 and the average first fall frost around Oct 2, for a growing season of about 143 days. For frost-tender plants, wait until May 24, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Castle Rock, CO weather station, 4 miles away, elevation 6,185 ft. Frost can come earlier in low spots and valleys and later near cities and large lakes.
Frost probability by date
Chance of a 32°F frost after the spring date, or before the fall date.
| Chance | Last spring frost | First fall frost |
|---|---|---|
| 10% | May 24 | Sep 17 |
| 20% | May 18 | Sep 23 |
| 30% | May 15 | Sep 27 |
| 40% | May 12 | Sep 30 |
| 50% | May 9 | Oct 2 |
| 60% | May 7 | Oct 5 |
| 70% | May 5 | Oct 8 |
| 80% | May 3 | Oct 12 |
| 90% | Apr 30 | Oct 16 |
Light frost vs. hard freeze
Average (50%) dates for each temperature. Tender plants are damaged at 36°F; most hardy crops survive until 28°F.
| Temperature | Last in spring | First in fall |
|---|---|---|
| Light frost (36°F) | May 21 | Sep 25 |
| Frost / freeze (32°F) | May 9 | Oct 2 |
| Hard freeze (28°F) | May 1 | Oct 12 |
Planting calendar for Castle Rock
Transplant May 16 – May 30
Transplant May 23 – Jun 6
Transplant May 23 – Jun 6
Transplant May 16 – May 30
Sow or transplant May 16 – May 30
Sow or transplant May 16 – May 30
Sow or transplant May 23 – Jun 6
Sow or transplant Apr 11 – Apr 25
Fall sowing Aug 7 – Sep 4
Fall sowing Aug 7 – Aug 28
Fall sowing Jul 24 – Aug 7
Sow or transplant Apr 11 – Apr 25
Fall sowing Jul 24 – Aug 21
Transplant Apr 25 – May 9
Fall sowing Jul 10 – Jul 24
Transplant Apr 18 – May 2
Fall sowing Jul 10 – Jul 24
Fall sowing Jul 10 – Jul 24
Fall sowing Aug 21 – Sep 11
Fall sowing Jul 24 – Aug 7
Plant Apr 11 – Apr 25
Based on the average last frost (May 9) and first frost (Oct 2). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.