Last frost date in Portsmouth, NH
The average last frost in Portsmouth is May 4. By May 18 the chance of another 32°F night drops to 1 in 10. The first fall frost usually arrives about October 8, which leaves 157 frost-free days. An early freeze before September 27 happens one year in ten.
- Safe after (10% risk)
- May 18
- Average first frost
- Oct 8
- Frost-free season
- 157 days
- Hard freeze (28°F) ends
- Apr 23
Frost likely Fri night, low 29°F
National Weather Service forecast, updated Oct 22, 12:57 UTC
- ThuOct 2235°possible frost
- FriOct 2329°frost
- SatOct 2430°frost
- SunOct 2534°possible frost
- MonOct 2641°
- TueOct 2736°possible frost
- WedOct 2837°
Planting calendar for Portsmouth
Windows count forward or back from the average frost dates above. Click a crop for dates across New Hampshire.
TomatoesMay 11–May 25
PumpkinsMay 18–Jun 1
SunflowersMay 4–May 25
CucumbersMay 18–May 25
CornMay 11–May 25
Sweet potatoesMay 25–Jun 8
WatermelonMay 18–Jun 1
Green beansMay 11–Jun 1
ZucchiniMay 11–May 25
OkraMay 25–Jun 8
PeppersMay 18–Jun 1
BasilMay 11–May 25
Butternut squashMay 11–May 25
CantaloupeMay 18–Jun 1
EggplantMay 18–Jun 1
PotatoesApr 6–Apr 20
OnionsMar 23–Apr 13
CarrotsApr 13–May 18
LettuceApr 20–May 11
BroccoliApr 6–Apr 20
BeetsApr 6–May 18
PeasMar 23–Apr 6
CabbageApr 6–Apr 20
RadishesMar 30–May 11
Brussels sproutsApr 20–May 4
SpinachMar 23–Apr 13
CilantroApr 20–May 11
KaleApr 6–Apr 20
Collard greensApr 6–Apr 20
TurnipsApr 6–Apr 20
DillMay 4–May 18
CeleryMay 11–May 18
CauliflowerApr 20–May 4
LeeksApr 20–May 4
Swiss chardApr 20–May 18
ParsleyApr 20–May 11
Tulip bulbsSep 24–Oct 29
GarlicSep 17–Oct 22
Daffodil bulbsSep 10–Oct 22
StrawberriesApr 6–Apr 20
AsparagusApr 6–Apr 20Frost probabilities
| Threshold | Spring, 90% chance later | Spring, 50% | Spring, 10% | Fall, 10% chance earlier | Fall, 50% | Fall, 90% |
|---|---|---|---|---|---|---|
| Light frost, 32°F | Apr 23 | May 4 | May 18 | Sep 27 | Oct 8 | Oct 24 |
| Hard freeze, 28°F | Apr 7 | Apr 23 | May 7 | Oct 5 | Oct 21 | Nov 5 |
Read the spring 10% column as the date after which only one year in ten still gets frost. That is the safer date for tomatoes, peppers and basil.
Where these numbers come from
NOAA station Greenland (USC00273626) sits 3.6 miles from the center of Portsmouth at 95 feet. Its averages cover 1991 to 2020. Low spots, valleys and open fields can keep getting frost a week or two after the station stops; city centers and lakeshores usually get less of it.
Questions
When is the last frost in Portsmouth, NH?
The average last frost date in Portsmouth is May 4, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after May 18.
When is the first frost in Portsmouth?
The first frost in fall usually comes around October 8. One year in ten it arrives before September 27.
How long is the growing season in Portsmouth?
About 157 days between the average last and first frost.
When should I plant tomatoes in Portsmouth?
Plant tomato seedlings outside from May 11 to May 25. Start seeds indoors six to eight weeks earlier.