Alton, IL planting zone & frost dates
Alton is in USDA hardiness zone 7a. The last spring frost usually comes around April 4 and the first fall frost around November 5, for a growing season of about 214 days.
Planting calendar for Alton
Dates are counted from the average last spring frost (April 4) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.
| Crop | When |
|---|---|
| Tomatoes | Start seeds indoors: Feb 7 – Feb 21 Transplant outdoors: Apr 11 – Apr 18 |
| Peppers | Start seeds indoors: Jan 24 – Feb 7 Transplant outdoors: Apr 18 – Apr 25 |
| Eggplant | Start seeds indoors: Jan 24 – Feb 7 Transplant outdoors: Apr 18 – Apr 25 |
| Broccoli | Start seeds indoors: Jan 24 – Feb 7 Transplant outdoors: Mar 7 – Mar 21 |
| Cabbage | Start seeds indoors: Jan 24 – Feb 7 Transplant outdoors: Mar 7 – Mar 21 |
| Onions (sets) | Plant outdoors: Mar 7 – Mar 21 |
| Peas | Sow outdoors: Feb 21 – Mar 7 |
| Spinach | Sow outdoors: Feb 21 – Mar 7 |
| Lettuce | Sow outdoors: Mar 7 – Mar 21 |
| Carrots | Sow outdoors: Mar 7 – Mar 21 |
| Potatoes | Plant outdoors: Mar 7 – Mar 21 |
| Beans | Sow outdoors: Apr 11 – Apr 18 |
| Sweet corn | Sow outdoors: Apr 11 – Apr 18 |
| Cucumbers | Sow outdoors: Apr 11 – Apr 18 |
| Squash & zucchini | Sow outdoors: Apr 11 – Apr 18 |
| Basil | Start seeds indoors: Feb 21 – Mar 7 Transplant outdoors: Apr 11 – Apr 18 |
Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Sep 10 (8 weeks before the average first fall frost on Nov 5).
Useful for zone 7a gardens
- Seed starting kit with dome — to start seeds indoors before the last frost
- LED grow light for seedlings — stops leggy seedlings
- Frost cloth / plant covers — for late spring and early fall frosts
- Soil thermometer — warm-season crops need soil above 60°F
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Frost risk in detail
| 90% chance | 50% chance | 10% chance | |
|---|---|---|---|
| Last 32°F frost in spring is after | Mar 18 | Apr 4 | Apr 19 |
| First 32°F frost in fall is before | Nov 21 | Nov 5 | Oct 25 |
How to read it: in spring there is a 10% chance of a frost after April 19, so that is a safe date for tender plants. In fall there is a 10% chance of frost before October 25. A hard freeze (28°F) usually ends around March 25.
Hardiness zone by ZIP code in Alton
- 62002 zone 7a
Nearby cities
- Upper Alton zone 7a, last frost Apr 4
- Godfrey zone 7a, last frost Apr 4
- Wood River zone 7a, last frost Apr 4
- Granite City zone 7a, last frost Apr 1
- Edwardsville zone 7a, last frost Apr 4
- Glen Carbon zone 7a, last frost Apr 4
- East Saint Louis zone 7a, last frost Apr 8
- Collinsville zone 7a, last frost Apr 8
Questions
What growing zone is Alton, IL?
Alton is in USDA Plant Hardiness Zone 7a (average extreme winter low 0°F to 5°F), according to the USDA 2023 map.
When is the last frost in Alton?
The average last spring frost (32°F) in Alton is April 4. There is still a 10% chance of frost until April 19.
When can I plant tomatoes in Alton?
Transplant tomatoes outdoors 1–2 weeks after the average last frost: around Apr 11 – Apr 18. Start seeds indoors 6–8 weeks before the last frost.
Frost dates: NOAA U.S. Climate Normals 1991–2020, station Alton - Melvin Price L&D, IL (USC00110137), 4.0 km (2.5 mi) from the city center, elevation 123 m, based on 25 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.