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Estimate frost dates by USDA zone with growing season and planting window calculations.
Frost dates are the average dates of the last spring frost and first fall frost for a region, used to determine the growing season length and safe planting windows.
| Zone | Last Spring | First Fall | Season |
|---|---|---|---|
| 3 | May 15 | Sep 15 | 123 days |
| 4 | May 1 | Oct 1 | 153 days |
| 5 | Apr 15 | Oct 15 | 183 days |
| 6 | Apr 1 | Oct 31 | 213 days |
| 7 | Mar 15 | Nov 15 | 245 days |
| 8 | Mar 1 | Nov 30 | 274 days |
| 9 | Feb 15 | Dec 15 | 303 days |
| 10 | Feb 1 | Dec 31 | 333 days |
Formula
Growing Season = First Fall Frost Date − Last Spring Frost DateGrowing Season = Number of frost-free days for outdoor gardening
Last Spring Frost = Average date of last freezing temp (≤0°C) in spring
First Fall Frost = Average date of first freezing temp (≤0°C) in fall
Worked Example
Zone 6 growing season
Did you know? The USDA Plant Hardiness Zone Map was updated in 2023, with about half of the country shifting to a warmer zone compared to the 2012 map (source: USDA ARS).
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Calculate growing season length and planting windows from USDA frost zone data.