When to plant in Glen Carbon, IL
USDA Zone 7aEverything below — frost dates, hardiness zone, and what to plant when in Glen Carbon, Illinois — is derived from the closest NOAA station with complete climate normals.
Heads up: the nearest complete-normals station is about 19 km from Glen Carbon, so your yard's frost dates can differ — a low spot or a paved city center can shift them by a week. Zone 7a means many perennials and even some tender shrubs overwinter in Glen Carbon, 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 Glen Carbon’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 Glen Carbon, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 28 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.
Glen Carbon planting FAQ
When is the last spring frost in Glen Carbon, IL?
Plan for the last spring frost in Glen Carbon around April 4 (the date it has a 50% chance of a 32°F freeze). Anything frost-sensitive should go out after it.
When is the first fall frost in Glen Carbon, IL?
In Glen Carbon, 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 Glen Carbon in?
Glen Carbon 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 Glen Carbon?
There are roughly 215 frost-free days in Glen Carbon (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 Glen Carbon?
In Glen Carbon, 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 Glen Carbon
An email when it’s time to start seeds, transplant, and sow — timed to Glen Carbon’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Edwardsville · 4 km
- Troy · 9 km
- Collinsville · 9 km
- Granite City · 13 km
- Wood River · 14 km
- Fairview Heights · 18 km
- O'Fallon · 19 km
- Spanish Lake · 20 km
Frost dates recorded at ALTON - MELVIN PRICE L&D, 19 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 Glen Carbon, IL — Frost Dates & Zone 7a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00110137. Retrieved from https://blissgarden.com/illinois/glen-carbon.