First and Last Frost Dates by State
When is the last spring frost? When does the first fall frost arrive? These dates determine your growing season and are essential for gardeners and farmers across the US.
What is a Frost Date?
Frost occurs when air temperatures drop to 32°F (0°C) or below. The "last spring frost date" is the average date of the final freeze in spring, after which tender plants can safely be planted outdoors. The "first fall frost date" is the average date of the season's first freeze, marking the end of the frost-free growing season.
How Frost Dates Are Calculated
Frost dates are statistical - they represent the date with a 50% probability of frost. Gardeners often use the 10% probability date (safer for tender plants) or the 90% probability date (more aggressive). This site calculates frost dates from monthly average lows: if the average low drops below 35°F, frost is possible; below 28°F, frost is likely.
Growing Season Length by Region
| Region | Last Spring Frost | First Fall Frost | Growing Season |
|---|---|---|---|
| Deep South (FL, GA, AL) | February 15 - March 15 | November 15 - December 1 | 270-300 days |
| Mid-Atlantic | April 1-15 | October 15-31 | 180-210 days |
| Midwest (IA, IL) | April 15-30 | October 1-15 | 155-175 days |
| Upper Midwest (MN, ND) | May 1-15 | September 15-30 | 120-145 days |
| Mountain West (CO, WY) | May 15 - June 1 | September 1-15 | 100-120 days |
| Pacific Northwest | March 15 - April 1 | October 31 - November 15 | 220-240 days |
Year-Round Frost-Free Zones
Southern Florida (Miami, Fort Lauderdale), Hawaii, and the extreme southern portions of Texas and California rarely or never experience frost. These areas can grow tropical plants year-round and have continuous growing seasons.
Microclimates Matter
Frost dates vary significantly within a single county. Cold air settles in valleys and low spots - a garden at the bottom of a slope may freeze 2-3 weeks earlier in fall than one at the top. Urban areas are typically warmer than surrounding rural areas due to the urban heat island effect.