Frost Dates for Janesville, WI 53546

Last spring frost May 6 · First fall frost October 4 · 151 frost-free days · USDA Zone 5b

Frost probability for 53546

Frost10%50%90%
Spring (last frost)May 21May 6April 21
Fall (first frost)September 21October 4October 17

Dates come from NOAA 1971–2000 freeze probabilities at the nearest reporting station (29.1 km away); the 50% date is the median year.

Frost dates by ZIP code in Janesville, WI

ZIPLast spring frost (50%)First fall frost (50%)Zone
53546May 6October 45b
53545May 2October 35b
53548May 2October 25b

Month by month in Janesville

MonthWhat to do
JanuaryPlan your garden layout and order seeds. Research varieties suited to your frost dates.
FebruaryStart the slowest-growing crops indoors: onions, leeks, and celery (10–12 weeks before last frost).
MarchStart peppers and eggplant indoors 8–10 weeks before your last frost (around May 6). Start tomatoes about two weeks later, 6–8 weeks before last frost.
AprilStart herbs, basil, and squash indoors (4–6 weeks before frost). Direct sow peas, spinach, and lettuce if soil is workable.
MayLast frost around May 6. Transplant cold-hardy crops (broccoli, kale, cabbage). Harden off tomato and pepper seedlings.
JuneFrost has passed. Transplant tomatoes, peppers, and basil outdoors. Direct sow beans, cucumbers, squash, and zucchini.
JulySuccession plant lettuce and greens. Keep beds weeded and watered consistently.
AugustHarvest regularly to encourage production. Monitor for pests and disease.
SeptemberFirst fall frost approaching (around October 4). Transplant fall brassicas. Sow spinach, arugula, and radishes.
OctoberFirst frost around October 4. Harvest tomatoes and peppers before frost. Cover cold-hardy crops with row covers to extend the season.
NovemberHarvest remaining cold-hardy crops: kale, carrots, and beets. Plant garlic bulbs for next year.
DecemberClean up spent plants. Add compost to beds. Rest, review, and plan next year's garden.

What grows in a 151-day season

Frequently Asked Questions

What is the last frost date for Janesville, WI (ZIP 53546)?

The median last spring frost date for Janesville, WI (ZIP code 53546) is around May 6. This is the 50th-percentile date — meaning half of all years see frost end before this date. Use the 10% and 90% dates to understand the full range of risk in your area.

What is the first fall frost date in Janesville, WI?

The median first fall frost date for Janesville, WI is around October 4. Plan to harvest or protect frost-sensitive crops like tomatoes and peppers at least a week before this date to avoid losses.

How long is the growing season in Janesville, WI?

The frost-free growing season in Janesville is about 151 days. This window — from your last spring frost to your first fall frost — is when warm-season vegetables thrive. Cold-hardy crops like kale, spinach, and peas can extend your season by weeks on either side.

What USDA hardiness zone is Janesville, WI?

Based on frost date patterns, Janesville falls approximately in 5b. USDA hardiness zones are determined by average annual minimum winter temperatures and guide both plant selection and planting timing for your location.

When should I start tomatoes indoors in Janesville, WI?

Start tomato seeds indoors 6–8 weeks before your last frost date (around May 6). For Janesville, that's roughly March 11 to March 25. Transplant outdoors 1–2 weeks after your last frost.

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