Portage, WI planting zone & frost dates

Portage is in USDA hardiness zone 5a. The last spring frost usually comes around April 28 and the first fall frost around October 10, for a growing season of about 164 days.

USDA hardiness zone5aavg. extreme winter low -20°F to -15°F

Average last spring frostApril 2890% chance of no frost after May 12

Average first fall frostOctober 1010% chance of frost by September 26

Growing season164 daysfrost-free days in an average year

Planting calendar for Portage

Dates are counted from the average last spring frost (April 28) using the typical timing recommended by U.S. extension services. Warm-season crops go out only after the danger of frost has passed and the soil has warmed.

Crop	When
Tomatoes	Start seeds indoors: Mar 3 – Mar 17 Transplant outdoors: May 5 – May 12
Peppers	Start seeds indoors: Feb 17 – Mar 3 Transplant outdoors: May 12 – May 19
Eggplant	Start seeds indoors: Feb 17 – Mar 3 Transplant outdoors: May 12 – May 19
Broccoli	Start seeds indoors: Feb 17 – Mar 3 Transplant outdoors: Mar 31 – Apr 14
Cabbage	Start seeds indoors: Feb 17 – Mar 3 Transplant outdoors: Mar 31 – Apr 14
Onions (sets)	Plant outdoors: Mar 31 – Apr 14
Peas	Sow outdoors: Mar 17 – Mar 31
Spinach	Sow outdoors: Mar 17 – Mar 31
Lettuce	Sow outdoors: Mar 31 – Apr 14
Carrots	Sow outdoors: Mar 31 – Apr 14
Potatoes	Plant outdoors: Mar 31 – Apr 14
Beans	Sow outdoors: May 5 – May 12
Sweet corn	Sow outdoors: May 5 – May 12
Cucumbers	Sow outdoors: May 5 – May 12
Squash & zucchini	Sow outdoors: May 5 – May 12
Basil	Start seeds indoors: Mar 17 – Mar 31 Transplant outdoors: May 5 – May 12

Fall garden: cool-season crops like lettuce, spinach and kale can be sown again around Aug 15 (8 weeks before the average first fall frost on Oct 10).

Useful for zone 5a gardens

Seed starting kit with dome — to start seeds indoors before the last frost
LED grow light for seedlings — stops leggy seedlings
Frost cloth / plant covers — for late spring and early fall frosts
Soil thermometer — warm-season crops need soil above 60°F
Cold frame / mini greenhouse — adds weeks to a short season

As an Amazon Associate, FrostZoneMap earns from qualifying purchases, at no extra cost to you.

Frost risk in detail

	90% chance	50% chance	10% chance
Last 32°F frost in spring is after	Apr 14	Apr 28	May 12
First 32°F frost in fall is before	Oct 23	Oct 10	Sep 26

How to read it: in spring there is a 10% chance of a frost after May 12, so that is a safe date for tender plants. In fall there is a 10% chance of frost before September 26. A hard freeze (28°F) usually ends around April 16.

Hardiness zone by ZIP code in Portage

53901 zone 5a

Nearby cities

Baraboo zone 5a, last frost May 5
Waunakee zone 5a, last frost May 1
Sun Prairie zone 5a, last frost May 1
Middleton zone 5b, last frost Apr 28
Madison zone 5a, last frost May 1
Verona zone 5a, last frost Apr 28
Fitchburg zone 5b, last frost May 1
Oregon zone 5a, last frost May 1

All cities in Wisconsin → · Other zone 5a cities →

Questions

What growing zone is Portage, WI?

Portage is in USDA Plant Hardiness Zone 5a (average extreme winter low -20°F to -15°F), according to the USDA 2023 map.

When is the last frost in Portage?

The average last spring frost (32°F) in Portage is April 28. There is still a 10% chance of frost until May 12.

When can I plant tomatoes in Portage?

Transplant tomatoes outdoors 1–2 weeks after the average last frost: around May 5 – May 12. Start seeds indoors 6–8 weeks before the last frost.

Frost dates: NOAA U.S. Climate Normals 1991–2020, station Portage Wwtp, WI (USC00476718), 2.3 km (1.4 mi) from the city center, elevation 239 m, based on 30 years of records. Hardiness zone: USDA Plant Hardiness Zone Map 2023 for the ZIP code nearest to the city center. Microclimates (valleys, hills, cities, coasts) can be warmer or colder: check the local forecast before planting. How we calculate the data.