When to plant in Alton, IL
USDA Zone 7aAlton, Illinois frost dates, USDA zone, and a full-year planting calendar, drawn from the nearest NOAA station and tuned to the local season.
Zone 7a means many perennials and even some tender shrubs overwinter in Alton, while your frost dates still decide when annuals go out.
Frost probability
ALTON - MELVIN PRICE L&D · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Alton’s own odds, recorded at ALTON - MELVIN PRICE L&D.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 1 | Apr 14 | Mar 31 | Oct 12 | Oct 27 | Nov 8 |
| 32°F | Apr 19 | Apr 4 | Mar 18 | Oct 25 | Nov 5 | Nov 21 |
| 28°F | Apr 9 | Mar 25 | Mar 6 | Nov 2 | Nov 16 | Dec 1 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in Alton, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 26 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Alton planting FAQ
When is the last spring frost in Alton, IL?
On average, the last spring frost in Alton is around April 4 (50% probability at 32°F, from 1991–2020 NOAA normals). Wait until after this date to set out tender plants like tomatoes and peppers.
When is the first fall frost in Alton, IL?
In Alton, the first 32°F freeze of fall lands around November 5 on average. Time your last harvests and any season-extension cover before it.
What hardiness zone is Alton in?
Alton is in USDA hardiness zone 7a. In zone 7a, winters are moderate — most common vegetables grow well in season.
How long is the growing season in Alton?
There are roughly 215 frost-free days in Alton (a long growing season), running from the average last frost around April 4 to the first fall frost near November 5.
When should I plant tomatoes in Alton?
In Alton, start tomato seeds indoors around February 7–February 21, then transplant seedlings outdoors around April 11 once the danger of frost has passed.
Never miss a window in Alton
An email when it’s time to start seeds, transplant, and sow — timed to Alton’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Wood River · 8 km
- Godfrey · 8 km
- Spanish Lake · 14 km
- Old Jamestown · 14 km
- Bellefontaine Neighbors · 18 km
- Edwardsville · 19 km
- Florissant · 19 km
- Granite City · 20 km
Frost dates recorded at ALTON - MELVIN PRICE L&D, 4 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Alton, IL — Frost Dates & Zone 7a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00110137. Retrieved from https://blissgarden.com/illinois/alton.