Last frost date in Boise City, ID
In Boise City, the last spring frost comes around April 24 in an average year. Wait until May 9 if you want 90% odds of no more frost. The first fall frost usually arrives about October 21, which leaves 179 frost-free days. An early freeze before October 5 happens one year in ten.
- Safe after (10% risk)
- May 9
- Average first frost
- Oct 21
- Frost-free season
- 179 days
- Hard freeze (28°F) ends
- Apr 2
Frost possible in low spots Fri night, low 36°F
National Weather Service forecast, updated Oct 22, 12:57 UTC
- ThuOct 2246°
- FriOct 2336°possible frost
- SatOct 2437°
- SunOct 2540°
- MonOct 2639°
- TueOct 2738°
- WedOct 2839°
Planting calendar for Boise City
Windows count forward or back from the average frost dates above. Click a crop for dates across Idaho.
TomatoesMay 1–May 15
PumpkinsMay 8–May 22
SunflowersApr 24–May 15
CucumbersMay 8–May 15
CornMay 1–May 15
Sweet potatoesMay 15–May 29
WatermelonMay 8–May 22
Green beansMay 1–May 22
ZucchiniMay 1–May 15
OkraMay 15–May 29
PeppersMay 8–May 22
BasilMay 1–May 15
Butternut squashMay 1–May 15
CantaloupeMay 8–May 22
EggplantMay 8–May 22
PotatoesMar 27–Apr 10
OnionsMar 13–Apr 3
CarrotsApr 3–May 8
LettuceApr 10–May 1
BroccoliMar 27–Apr 10
BeetsMar 27–May 8
PeasMar 13–Mar 27
CabbageMar 27–Apr 10
RadishesMar 20–May 1
Brussels sproutsApr 10–Apr 24
SpinachMar 13–Apr 3
CilantroApr 10–May 1
KaleMar 27–Apr 10
Collard greensMar 27–Apr 10
TurnipsMar 27–Apr 10
DillApr 24–May 8
CeleryMay 1–May 8
CauliflowerApr 10–Apr 24
LeeksApr 10–Apr 24
Swiss chardApr 10–May 8
ParsleyApr 10–May 1
Tulip bulbsOct 7–Nov 11
GarlicSep 30–Nov 4
Daffodil bulbsSep 23–Nov 4
StrawberriesMar 27–Apr 10
AsparagusMar 27–Apr 10Frost probabilities
| Threshold | Spring, 90% chance later | Spring, 50% | Spring, 10% | Fall, 10% chance earlier | Fall, 50% | Fall, 90% |
|---|---|---|---|---|---|---|
| Light frost, 32°F | Apr 4 | Apr 24 | May 9 | Oct 5 | Oct 21 | Nov 5 |
| Hard freeze, 28°F | Mar 10 | Apr 2 | Apr 25 | Oct 17 | Oct 31 | Nov 19 |
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 Boise Air Terminal (USW00024131) sits 2.2 miles from the center of Boise City at 2,814 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 Boise City, ID?
The average last frost date in Boise City is April 24, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after May 9.
When is the first frost in Boise City?
The first frost in fall usually comes around October 21. One year in ten it arrives before October 5.
How long is the growing season in Boise City?
About 179 days between the average last and first frost.
When should I plant tomatoes in Boise City?
Plant tomato seedlings outside from May 1 to May 15. Start seeds indoors six to eight weeks earlier.