Frost Dates: First and last frost dates for Hartford, WI

ℹ️ How to read these charts for the spring

As spring unfolds, the risk of frost gradually decreases each day until your tender plants are finally safe. The probabilities shown in the chart help you make smart decisions about when to plant.

While frost typically forms at 32°F, tender plants can be damaged even when temperatures are slightly higher. Air temperatures are often measured several feet above the ground, but temperatures at plant level can be several degrees colder. Protected areas like porches help by blocking radiational cooling. Given these variables, we consider 36°F the "caution zone" for frost-sensitive plants.

Key dates for your spring planting:

  • By June 14, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around May 27, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before May 16, there's still an 80% risk of frost — too early for tomatoes and other tender plants unless you're prepared to protect them

If the 10-day forecast shows no temperatures below 40°F, you might safely plant earlier than the above dates suggest. Many gardeners watch for this weather window to get a head start on the growing season.

In the Spring
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Last 16° Apr 8 Apr 3 Mar 30 Mar 27 Mar 24 Mar 21 Mar 18 Mar 14 Mar 9
Last 20° Apr 17 Apr 13 Apr 9 Apr 7 Apr 4 Apr 1 Mar 29 Mar 26 Mar 21
Last 24° Apr 27 Apr 22 Apr 19 Apr 16 Apr 13 Apr 10 Apr 7 Apr 4 Mar 30
Last 28° May 12 May 7 May 3 Apr 30 Apr 27 Apr 24 Apr 21 Apr 17 Apr 12
Last 32° May 29 May 23 May 19 May 16 May 12 May 9 May 6 May 2 Apr 26
Last 36° Jun 14 Jun 8 Jun 3 May 31 May 27 May 24 May 20 May 16 May 10

ℹ️ How to read these charts for the fall

As summer ends in Hartford, WI, nighttime temperatures begin to drop, and your risk of frost increases with each passing day. Knowing when to expect frost helps you harvest sensitive crops and extend your growing season with protection methods.

The chart below shows the probability of experiencing specific temperatures on various dates. Here's what this means for your garden:

1
Early warning: Around September 22, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By September 30, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By October 9, there's an 80% chance of seeing 32°F — most tender plants will be damaged without protection
4
Another perspective: You have only a 1 in 5 chance of making it past October 9 without a freezing night

These probabilities help you time your end-of-season harvests and know when to apply protective measures like row covers, cloches, or cold frames to extend your harvest.

In the Fall
Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
First 16° Nov 3 Nov 8 Nov 12 Nov 16 Nov 19 Nov 22 Nov 25 Nov 29 Dec 4
First 20° Oct 21 Oct 26 Oct 29 Nov 1 Nov 4 Nov 7 Nov 10 Nov 13 Nov 18
First 24° Oct 3 Oct 10 Oct 15 Oct 19 Oct 23 Oct 27 Oct 31 Nov 4 Nov 11
First 28° Sep 23 Sep 28 Oct 1 Oct 4 Oct 7 Oct 9 Oct 12 Oct 15 Oct 20
First 32° Sep 18 Sep 22 Sep 25 Sep 28 Sep 30 Oct 3 Oct 5 Oct 9 Oct 13
First 36° Sep 7 Sep 11 Sep 14 Sep 16 Sep 18 Sep 20 Sep 22 Sep 25 Sep 29

📍 Frost Dates for other nearby locations

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Data is provided by the NOAA National Centers for Environmental Information.