Frost dates for 53545Janesville, WI
The average last spring frost in Janesville is April 26 and the average first fall frost is October 15, giving a typical growing season of about 170 days. Dates are based on NOAA 1991-2020 climate normals.
- Average last spring frost
- Apr 26
- Average first fall frost
- Oct 15
- Growing season
- 170 days
Safer after May 11 (1-in-10 risk)
Possible by Oct 1 (1-in-10 risk)
Last frost typically in 181 days
Frost risk by date
NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.
| Temperature | Last spring: 90% / 50% / 10% chance | First fall: 10% / 50% / 90% chance | Growing season (50%) | Years with at least one |
|---|---|---|---|---|
| Light frost (36°F) | Apr 22 · May 6 · May 23 | Sep 22 · Oct 4 · Oct 16 | 149 days | 100% |
| Frost / freeze (32°F) | Apr 13 · Apr 26 · May 11 | Oct 1 · Oct 15 · Oct 27 | 170 days | 100% |
| Hard freeze (28°F) | Apr 2 · Apr 15 · Apr 29 | Oct 12 · Oct 26 · Nov 7 | 193 days | 100% |
Planting calendar for Janesville
Planting windows from the University of Maryland Extension calendar, shifted to your average frost dates. Use them as a starting point and adjust for seed packet instructions and local conditions.
| Crop | Task | Window |
|---|---|---|
| Tomatoes | Start seeds indoors | Mar 26 – Jun 1 |
| Tomatoes | Transplant outdoors | May 12 – Jun 25 |
| Peppers | Start seeds indoors | Mar 26 – Apr 26 |
| Peppers | Transplant outdoors | May 26 – Jun 26 |
| Eggplant | Start seeds indoors | Apr 12 – May 11 |
| Eggplant | Transplant outdoors | May 26 – Jun 26 |
| Cucumbers | Sow outdoors | May 26 – Jul 5 |
| Summer squash | Sow outdoors | May 12 – Jun 26 |
| Winter squash & pumpkins | Sow outdoors | May 26 – Jun 26 |
| Snap beans | Sow outdoors | May 12 – Jul 28 |
| Sweet corn | Sow outdoors | May 12 – Jun 25 |
| Watermelon & cantaloupe | Sow outdoors | May 26 – Jun 26 |
| Okra | Sow outdoors | May 19 – Jun 11 |
| Peas | Sow outdoors (spring) | Mar 26 – May 11 |
| Potatoes | Plant outdoors (spring) | Mar 26 – May 26 |
| Onions | Start seeds indoors (spring) | Feb 12 – Mar 11 |
| Onions | Transplant outdoors (spring) | Apr 12 – May 11 |
| Broccoli | Start seeds indoors (spring) | Mar 8 – Apr 11 |
| Broccoli | Transplant outdoors (spring) | Apr 12 – May 11 |
| Broccoli | Start seeds indoors (fall) | Jun 15 – Jun 25 |
| Broccoli | Transplant outdoors (fall) | Jul 15 – Jul 26 |
| Cabbage | Start seeds indoors (spring) | Feb 26 – Mar 26 |
| Cabbage | Transplant outdoors (spring) | Mar 26 – Apr 26 |
| Cabbage | Start seeds indoors (fall) | Jun 5 – Jul 5 |
| Cabbage | Transplant outdoors (fall) | Jul 5 – Aug 5 |
| Leaf lettuce | Sow outdoors (spring) | Mar 26 – Jun 11 |
| Leaf lettuce | Sow outdoors (fall) | Jul 5 – Aug 21 |
| Spinach | Sow outdoors (spring) | Mar 19 – May 2 |
| Spinach | Sow outdoors (fall) | Jul 22 – Aug 26 |
| Radishes | Sow outdoors (spring) | Mar 26 – May 16 |
| Radishes | Sow outdoors (fall) | Jul 5 – Sep 5 |
| Kale | Sow outdoors (spring) | Apr 12 – May 2 |
| Kale | Sow outdoors (fall) | Jun 28 – Aug 5 |
| Carrots | Sow outdoors (spring) | Apr 26 – Jun 11 |
| Carrots | Sow outdoors (fall) | Jun 5 – Jul 21 |
| Garlic | Plant outdoors (fall) | Oct 5 – Nov 5 |
Where these dates come from
ZIP code 53545 is matched to the NOAA station Afton - Janesville Wwtp, WI, 11.1 km away, at 762 ft elevation (140 ft lower than the ZIP code's center). Nearby stations for comparison:
| Station | Elevation | Avg last frost | Avg first frost |
|---|---|---|---|
| Afton - Janesville Wwtp, WI (used) | 762 ft | Apr 26 | Oct 15 |
| Ft Atkinson, WI | 800 ft | Apr 28 | Oct 13 |
| Stoughton, WI | 840 ft | Apr 30 | Oct 11 |
| Clinton Wwtp, WI | 924 ft | Apr 30 | Oct 10 |
Frost dates near Janesville
- Janesville, WI 53547 · last Apr 26, first Oct 15
- Milton, WI 53563 · last Apr 28, first Oct 13
- Edgerton, WI 53534 · last Apr 30, first Oct 11
- Afton, WI 53501 · last Apr 26, first Oct 15
- Hanover, WI 53542 · last Apr 26, first Oct 15
- Footville, WI 53537 · last Apr 26, first Oct 15
- Avalon, WI 53505 · last Apr 30, first Oct 10
- Beloit, WI 53511 · last May 1, first Oct 12
Frequently asked questions
- When is the last frost in Janesville, WI?
- For ZIP code 53545, the average last spring frost (32°F) is April 26, based on NOAA 1991-2020 climate normals for the Afton - Janesville Wwtp, WI weather station. There is a 1-in-10 chance of a frost after May 11.
- When is the first frost in Janesville, WI?
- The average first fall frost (32°F) is October 15. There is a 1-in-10 chance of frost by October 1, so tender plants are at risk from that point on.
- How long is the growing season in 53545?
- In half of years, the frost-free season (between the last and first 32°F frost) is at least 170 days long.
- Are these frost dates a forecast?
- No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.