White Harbor Labs › Frost Dates › States › New Hampshire
Frost Dates in New Hampshire
First and last frost dates across New Hampshire, computed from 16 NOAA weather stations (1991–2020 climate normals). Your exact date depends on your city and microclimate — use the ZIP lookup on the main tool for a station-specific answer.
Last spring frost
May 12
statewide median · range Apr 21–May 31
First fall frost
Oct 2
statewide median · range Sep 21–Oct 19
Growing season
143 days
median · range 112–180
Stations used
16
NOAA 1991–2020 normals
Frost dates by city
Median dates from the nearest NOAA station to each city. The "cautious" date is the 10% spring value — planting after it means only a ~10% chance of a later frost.
| City | Nearest station | Last spring frost | First fall frost | Growing season | Safe transplant |
|---|---|---|---|---|---|
| Manchester | Manchester Ap · 4 mi | Apr 21 (cautious: May 6) | Oct 19 | 180 days | May 5 |
| Nashua | Lowell (MA) · 11 mi | Apr 30 (cautious: May 10) | Oct 10 | 164 days | May 14 |
| Concord | Concord Asos · 2 mi | May 8 (cautious: May 22) | Oct 3 | 146 days | May 22 |
How frost varies across New Hampshire
Spring frost timing spans about 40 days across the state. Manchester in southern New Hampshire typically sees its last spring frost around April 21, while Colebrook in northern New Hampshire doesn't clear frost until about May 31. Within any city, low spots and valleys run colder than the station average; areas near buildings and pavement run warmer.
When to plant in New Hampshire
As a rule of thumb, cool-season crops (lettuce, peas, spinach) can go in 2–4 weeks before your last spring frost; warm-season transplants (tomatoes, peppers) should wait about 2 weeks after it — around May 26 for the statewide median. Check your city's row above rather than the statewide median: a 40-day statewide spread makes the city-level date the one that matters.
These are climate normals (what's typical), not forecasts. For the current year, watch the 10-day forecast around your planting date.
How this is computed
Statewide medians are the median of the 16 NOAA stations' median frost dates — half the stations run earlier, half later. City rows use the nearest station with 30-year freeze records. Dates are 32°F freeze probabilities from NOAA NCEI 1991–2020 U.S. Climate Normals; nothing is estimated or interpolated.
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Frequently asked questions
When is the last frost date in New Hampshire?
The statewide median last spring frost is May 12, but it ranges from April 21 to May 31 depending on where in the state you are. Use your city's row in the table above, or the ZIP lookup on the main tool, for a station-specific date.
When can I plant tomatoes outside in New Hampshire?
Warm-season transplants like tomatoes should wait about two weeks after your last spring frost — around May 26 for the statewide median. Your city may differ by weeks; check the "safe transplant" column in the city table.
How long is the growing season in New Hampshire?
The median growing season across 16 NOAA stations is 143 days, ranging from 112 to 180 days by location.
Why do frost dates vary so much within New Hampshire?
Frost timing follows latitude, elevation, and local terrain. Across New Hampshire, last spring frost dates span about 40 days — from around April 21 near Manchester to May 31 near Colebrook. Microclimates (low spots, valleys, urban heat) shift dates further at the garden level.
Where does this data come from?
All frost dates are computed from the NOAA National Centers for Environmental Information 1991–2020 U.S. Climate Normals freeze data (public domain), using each station's 32°F freeze probability statistics. No dates are estimated or interpolated.