How Frost Dates Are Determined
The chart below shows the average dates for the last spring frost and the first fall/winter frost dates for each USDA Hardiness Zone. These dates are typically defined by the day where there’s a 50% chance of being frost-free. If you want to ensure the safety of your plants, you may want to adjust these dates by a full two weeks (forward for spring, backward for fall/winter).
Be aware that within an individual hardiness zone, the dates for first and last frost can significantly vary. Within a single zone, the average dates can vary by as much as a week. If you do not know your planting zone, refer to the official USDA zone map.
Hardiness Zone May Not Always Be Accurate
A more precise way to determine your planting dates is to use one of the many interactive maps that allow you to determine planting dates based on your zip code. Type in your zip code to receive detailed information on average temperatures for your location. Many of these are available, but I have found this one to be the most accurate.
This information is useful both in terms of knowing when to sow seeds as well as figuring out how late in the season you can plant perennials, trees, and shrubs.
General Last and First Frost Dates, by Hardiness Zone
|USDA Zone||Last Frost Date||First Frost Date|
|1||June 1-30||July 1-31|
|2||May 16-31||Aug 1-31|
|3||May 1-15||Sep 1-30|
|4||April 16-30||Oct 1-15|
|5||April 1-15||Oct 16-31|
|6||Mar 16-30||Nov 1-15|
|7||Mar 1-15||Nov 16-30|
|8||Feb 1-28||Dec 1-15|
|9||Jan 1-30||Dec 16-31|
|10||Rare or no Freeze||Rare or no Freeze|