Last frost date in Alton, IL
The average last frost in Alton is April 4. By April 19 the chance of another 32°F night drops to 1 in 10. The first fall frost usually arrives about November 5, which leaves 214 frost-free days. An early freeze before October 25 happens one year in ten.
- Safe after (10% risk)
- Apr 19
- Average first frost
- Nov 5
- Frost-free season
- 214 days
- Hard freeze (28°F) ends
- Mar 25
No frost in the next 7 nights
National Weather Service forecast, updated Oct 22, 12:57 UTC
- ThuOct 2247°
- FriOct 2346°
- SatOct 2448°
- SunOct 2551°
- MonOct 2650°
- TueOct 2746°
- WedOct 2848°
Planting calendar for Alton
Windows count forward or back from the average frost dates above. Click a crop for dates across Illinois.
TomatoesApr 11–Apr 25
PumpkinsApr 18–May 2
SunflowersApr 4–Apr 25
CucumbersApr 18–Apr 25
CornApr 11–Apr 25
Sweet potatoesApr 25–May 9
WatermelonApr 18–May 2
Green beansApr 11–May 2
ZucchiniApr 11–Apr 25
OkraApr 25–May 9
PeppersApr 18–May 2
BasilApr 11–Apr 25
Butternut squashApr 11–Apr 25
CantaloupeApr 18–May 2
EggplantApr 18–May 2
PotatoesMar 7–Mar 21
OnionsFeb 21–Mar 14
CarrotsMar 14–Apr 18
LettuceMar 21–Apr 11
BroccoliMar 7–Mar 21
BeetsMar 7–Apr 18
PeasFeb 21–Mar 7
CabbageMar 7–Mar 21
RadishesFeb 28–Apr 11
Brussels sproutsMar 21–Apr 4
SpinachFeb 21–Mar 14
CilantroMar 21–Apr 11
KaleMar 7–Mar 21
Collard greensMar 7–Mar 21
TurnipsMar 7–Mar 21
DillApr 4–Apr 18
CeleryApr 11–Apr 18
CauliflowerMar 21–Apr 4
LeeksMar 21–Apr 4
Swiss chardMar 21–Apr 18
ParsleyMar 21–Apr 11
Tulip bulbsOct 22–Nov 26
GarlicOct 15–Nov 19
Daffodil bulbsOct 8–Nov 19
StrawberriesMar 7–Mar 21
AsparagusMar 7–Mar 21Frost probabilities
| Threshold | Spring, 90% chance later | Spring, 50% | Spring, 10% | Fall, 10% chance earlier | Fall, 50% | Fall, 90% |
|---|---|---|---|---|---|---|
| Light frost, 32°F | Mar 18 | Apr 4 | Apr 19 | Oct 25 | Nov 5 | Nov 21 |
| Hard freeze, 28°F | Mar 6 | Mar 25 | Apr 9 | Nov 2 | Nov 16 | Dec 1 |
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 Alton - Melvin Price L&d (USC00110137) sits 2.6 miles from the center of Alton at 405 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 Alton, IL?
The average last frost date in Alton is April 4, based on NOAA 1991–2020 climate normals. There is a 10% chance of frost after April 19.
When is the first frost in Alton?
The first frost in fall usually comes around November 5. One year in ten it arrives before October 25.
How long is the growing season in Alton?
About 214 days between the average last and first frost.
When should I plant tomatoes in Alton?
Plant tomato seedlings outside from April 11 to April 25. Start seeds indoors six to eight weeks earlier.
Nearby in Illinois
- EdwardsvilleApr 4
- Granite CityApr 4
- CollinsvilleApr 8
- O'FallonApr 12
- BellevilleApr 12
- SpringfieldApr 15
- DecaturApr 14
- CarbondaleApr 9
- QuincyApr 8
- PekinApr 16
- BloomingtonApr 25
- East PeoriaApr 16