When to plant in Janesville, WI
USDA Zone 5bEverything below — frost dates, hardiness zone, and what to plant when in Janesville, Wisconsin — is derived from the closest NOAA station with complete climate normals.
Zone 5b means Janesville sees real winter cold, but a good range of perennials survive; the frost dates above govern when annual vegetables go out.
The average first fall frost in Janesville is now 6 days later than in the 1981–2010 normals. See how frost dates are shifting nationwide →
Frost probability
AFTON - JANESVILLE WWTP · 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 Janesville’s own odds, recorded at AFTON - JANESVILLE WWTP.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 23 | May 6 | Apr 22 | Sep 22 | Oct 4 | Oct 16 |
| 32°F | May 11 | Apr 26 | Apr 13 | Oct 1 | Oct 15 | Oct 27 |
| 28°F | Apr 29 | Apr 15 | Apr 2 | Oct 12 | Oct 26 | Nov 7 |
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 Janesville, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 20 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.
Janesville planting FAQ
When is the last spring frost in Janesville, WI?
Janesville's average last spring frost falls near April 26 — the 50% mark at 32°F in the 1991–2020 normals. Hold tender transplants until the risk has passed, then plant out.
When is the first fall frost in Janesville, WI?
Expect Janesville's first fall frost near October 15 — a 50% chance of 32°F by that date. Bring in or cover tender crops ahead of it.
What hardiness zone is Janesville in?
Janesville is in USDA hardiness zone 5b. In zone 5b, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Janesville?
There are roughly 172 frost-free days in Janesville (a moderate growing season), running from the average last frost around April 26 to the first fall frost near October 15.
When should I plant tomatoes in Janesville?
In Janesville, start tomato seeds indoors around March 1–March 15, then transplant seedlings outdoors around May 3 once the danger of frost has passed.
Never miss a window in Janesville
An email when it’s time to start seeds, transplant, and sow — timed to Janesville’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Beloit · 18 km
- Whitewater · 28 km
- Roscoe · 29 km
- Fort Atkinson · 30 km
- Stoughton · 32 km
- Machesney Park · 35 km
- Loves Park · 39 km
- Elkhorn · 39 km
Frost dates recorded at AFTON - JANESVILLE WWTP, 7 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 Janesville, WI — Frost Dates & Zone 5b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00470045. Retrieved from https://blissgarden.com/wisconsin/janesville.