When to plant in Castle Pines, CO
USDA Zone 5bEverything below — frost dates, hardiness zone, and what to plant when in Castle Pines, Colorado — is derived from the closest NOAA station with complete climate normals.
Zone 5b means Castle Pines sees real winter cold, but a good range of perennials survive; the frost dates above govern when annual vegetables go out.
Frost probability
CASTLE ROCK · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Castle Pines’s own odds, recorded at CASTLE ROCK.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | Jun 6 | May 21 | May 9 | Sep 11 | Sep 25 | Oct 7 |
| 32°F | May 24 | May 9 | Apr 30 | Sep 17 | Oct 2 | Oct 16 |
| 28°F | May 14 | May 1 | Apr 17 | Sep 26 | Oct 12 | Oct 25 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in Castle Pines, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 12 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Castle Pines planting FAQ
When is the last spring frost in Castle Pines, CO?
On average, the last spring frost in Castle Pines is around May 9 (50% probability at 32°F, from 1991–2020 NOAA normals). Wait until after this date to set out tender plants like tomatoes and peppers.
When is the first fall frost in Castle Pines, CO?
Expect Castle Pines's first fall frost near October 2 — a 50% chance of 32°F by that date. Bring in or cover tender crops ahead of it.
What hardiness zone is Castle Pines in?
Castle Pines is in USDA hardiness zone 5b. In zone 5b, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Castle Pines?
There are roughly 146 frost-free days in Castle Pines (a short growing season), running from the average last frost around May 9 to the first fall frost near October 2.
When should I plant tomatoes in Castle Pines?
In Castle Pines, start tomato seeds indoors around March 14–March 28, then transplant seedlings outdoors around May 16 once the danger of frost has passed.
Never miss a window in Castle Pines
An email when it’s time to start seeds, transplant, and sow — timed to Castle Pines’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Lone Tree · 8 km
- Parker · 9 km
- Castle Rock · 10 km
- The Pinery · 11 km
- Highlands Ranch · 12 km
- Centennial · 14 km
- Cherry Creek · 16 km
- Greenwood Village · 17 km
Frost dates recorded at CASTLE ROCK, 7 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Castle Pines, CO — Frost Dates & Zone 5b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00051401. Retrieved from https://blissgarden.com/colorado/castle-pines.