Frost Dates for Janesville, WI
In Janesville, WI, the average last spring frost is around Apr 26 and the average first fall frost around Oct 15, for a growing season of about 170 days. For frost-tender plants, wait until May 11, when the chance of frost drops to 10%.
Based on NOAA 1991–2020 records from the Afton - Janesville Wwtp, WI weather station, 4 miles away, elevation 762 ft. Frost can come earlier in low spots and valleys and later near cities and large lakes.
Frost probability by date
Chance of a 32°F frost after the spring date, or before the fall date.
| Chance | Last spring frost | First fall frost |
|---|---|---|
| 10% | May 11 | Oct 1 |
| 20% | May 5 | Oct 6 |
| 30% | May 1 | Oct 10 |
| 40% | Apr 29 | Oct 12 |
| 50% | Apr 26 | Oct 15 |
| 60% | Apr 23 | Oct 17 |
| 70% | Apr 20 | Oct 20 |
| 80% | Apr 17 | Oct 23 |
| 90% | Apr 13 | Oct 27 |
Light frost vs. hard freeze
Average (50%) dates for each temperature. Tender plants are damaged at 36°F; most hardy crops survive until 28°F.
| Temperature | Last in spring | First in fall |
|---|---|---|
| Light frost (36°F) | May 6 | Oct 4 |
| Frost / freeze (32°F) | Apr 26 | Oct 15 |
| Hard freeze (28°F) | Apr 15 | Oct 26 |
Planting calendar for Janesville
Transplant May 3 – May 17
Transplant May 10 – May 24
Transplant May 10 – May 24
Transplant May 3 – May 17
Sow or transplant May 3 – May 17
Sow or transplant May 3 – May 17
Sow or transplant May 10 – May 24
Sow or transplant Mar 29 – Apr 12
Fall sowing Aug 20 – Sep 17
Fall sowing Aug 20 – Sep 10
Fall sowing Aug 6 – Aug 20
Sow or transplant Mar 29 – Apr 12
Fall sowing Aug 6 – Sep 3
Transplant Apr 12 – Apr 26
Fall sowing Jul 23 – Aug 6
Transplant Apr 5 – Apr 19
Fall sowing Jul 23 – Aug 6
Fall sowing Jul 23 – Aug 6
Fall sowing Sep 3 – Sep 24
Fall sowing Aug 6 – Aug 20
Plant Mar 29 – Apr 12
Based on the average last frost (Apr 26) and first frost (Oct 15). The dashed lines mark those dates. Seed packets list days to maturity; adjust for your varieties.