Frost dates · USDA zone 5b
Frost dates for Castle Rock, CO
Castle Rock, CO sees its last 32 °F night of spring around May 9 and its first of fall around October 2 — a 143-day freeze-free season in a typical year.
Pick a sauce; the Plan Builder runs this station's dates and hands back the calendar, plant count and gear list.
Freeze odds, by date
| Odds | Last spring freeze after | First fall freeze before |
|---|---|---|
| 9 years in 10 | Apr 30 | Oct 16 |
| Median — 1 year in 2 | May 9 | Oct 2 |
| 1 year in 10 | May 24 | Sep 17 |
The top row is the risky edge: in 9 years of 10 a spring freeze still comes after it, so tender transplants set out then need cover. The bottom row is the cautious date — only 1 year in 10 freezes after it — and the one to plan uncovered tender transplants against. Freeze-free season: 143 days median, at least 124 in 9 years of 10, at least 161 days in 1 year of 10. NOAA ranks season length year by year, so it is not the gap between two rows above. A hard freeze (28 °F) has a median last date of May 1 and first of Oct 12.
Castle Rock planting calendar, 2027
Every row runs from the median last frost (May 9) and median first frost (Oct 2) above, using each cultivar's days to maturity. Same engine as the Plan Builder.
| Crop | Start indoors | Transplant / plant | First harvest | Days |
|---|---|---|---|---|
| Hardneck GarlicSiberian (porcelain hardneck) | — | Oct 15prior fall | Jun 12 | 240 from sow |
| Spanish OnionYellow Sweet Spanish (long-day) | Feb 14 | Apr 11 | Jul 30 | 110 from transplant |
| Mustard greensGarnet Giant (Brassica juncea) | Direct sow | May 9 | Jun 8 | 30 from sow |
| CilantroSlow Bolt (Coriandrum sativum) | Apr 25 | Apr 25 | Jun 9 | 45 from sow |
| Genovese BasilGenovese | Apr 11 | May 23 | Jul 22 | 60 from transplant |
| CayenneLong Slim Cayenne (Capsicum annuum) | Mar 14 | May 16 | Jul 30 | 75 from transplant |
| HabaneroOrange Habanero (Capsicum chinense) | Feb 28 | May 23 | Aug 26 | 95 from transplant |
| JalapeñoEarly Jalapeño (Capsicum annuum) | Mar 14 | May 16 | Jul 30 | 75 from transplant |
| Marconi Red PepperMarconi Red (Capsicum annuum) | Mar 14 | May 16 | Aug 4 | 80 from transplant |
| SerranoSerrano Tampiqueño (Capsicum annuum) | Mar 14 | May 16 | Aug 4 | 80 from transplant |
| Nantes CarrotScarlet Nantes | Apr 25 | Apr 25 | Jul 4 | 70 from sow |
| TomatilloToma Verde | Mar 28 | May 16 | Jul 25 | 70 from transplant |
| Roma TomatoRoma VF (determinate paste) | Mar 28 | May 16 | Jul 30 | 75 from transplant |
| San Marzano TomatoSan Marzano (indeterminate paste) | Mar 28 | May 16 | Aug 4 | 80 from transplant |
Tight means first harvest lands within two weeks of the median first fall frost: start that crop indoors on time or cover it in fall.
What sauce can Castle Rock grow?
Each sauce, scheduled for a Castle Rock container garden: when the first seeds go in and when enough fruit has ripened for one batch.
Castle Rock frost questions
When is the last frost in Castle Rock, CO?
The median last 32 °F freeze at CASTLE ROCK, CO is May 9: half of years see a later one. One year in ten, a freeze still comes after May 24; nine years in ten, it comes after April 30. Source: NOAA NCEI 1991–2020 U.S. Climate Normals.
When is the first frost in Castle Rock, CO?
The median first 32 °F freeze of fall is October 2. One year in ten it arrives before September 17; nine years in ten, before October 16.
How long is the growing season in Castle Rock, CO?
143 days between the last spring and first fall 32 °F freeze in a median year. Nine years in ten the season runs at least 124 days; one year in ten, at least 161 days.
What growing zone is Castle Rock, CO?
USDA hardiness zone 5b, per the 2023 USDA Plant Hardiness Zone Map for ZIP 80109. A zone describes the coldest winter night, not when frost ends, so it is the wrong number for a planting calendar — the frost dates on this page are the right one.
When should I plant tomatoes in Castle Rock, CO?
Start Roma VF (determinate paste) seeds indoors around Mar 28 and transplant around May 16, 1 week after the median last frost. To cut the freeze risk to one year in ten, wait for May 24. First ripe fruit lands around Jul 30.
When should I plant peppers in Castle Rock, CO?
Sow jalapeño indoors on a heat mat around Mar 14; transplant no earlier than May 16, and wait past it until nights hold above 50 °F — that can run weeks later. First green pods around Jul 30.
Nearby in Colorado
- Parkerlast frost May 9
- Centenniallast frost May 5
- Littletonlast frost May 2
- Auroralast frost May 5
- Lakewoodlast frost May 3
- Denverlast frost May 4
All Colorado frost dates → · How frost-date math drives a sowing calendar →