Colorado Planting Guide & Growing Season
Colorado is in USDA hardiness zone 3b-7a with a growing season of 145 days. The average last spring frost is May 10 and the average first fall frost is Oct 1. Climate data based on Denver.
Growing Conditions in Colorado
How Colorado Compares
Compare Colorado's growing conditions with states that have similar climates.
| State | USDA Zone | Last Frost | First Frost | Season (days) |
|---|---|---|---|---|
| Colorado (CO) | 3b-7a | May 10 | Oct 1 | 145 |
| Alabama (AL) | 7a-8b | Mar 15 | Nov 5 | 235 |
| Alaska (AK) | 1a-7b | May 30 | Sep 5 | 100 |
| Arizona (AZ) | 4b-10b | Mar 1 | Nov 15 | 260 |
| Arkansas (AR) | 6b-8a | Apr 1 | Oct 25 | 210 |
| California (CA) | 4b-11a | Feb 15 | Nov 30 | 290 |
Frequently Asked Questions About Gardening in Colorado
When should I start seeds indoors in Colorado?
In Colorado, the average last frost date is May 10. Start most seeds indoors 6-8 weeks before this date. The USDA hardiness zone for Colorado is 3b-7a, with a growing season of approximately 145 days.
What USDA hardiness zone is Colorado?
Colorado falls in USDA hardiness zones 3b-7a. This affects which perennial plants will survive winter and influences optimal planting times.
When is the first frost in Colorado?
The average first frost date in Colorado is Oct 1. Plan to harvest cold-sensitive crops before this date or protect them with row covers.
How long is the growing season in Colorado?
Colorado has an average growing season of 145 days, from the last frost (May 10) to first frost (Oct 1). This shorter season requires starting many crops indoors and choosing quick-maturing varieties.
Plan Your Garden
Use our seed starting calculator to get personalized planting dates, or browse all states.