Frost Dates: First and last frost dates for Grand Portage, MN

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 July 8, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around June 21, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before June 10, 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° May 28 May 16 May 6 Apr 28 Apr 21 Apr 14 Apr 6 Mar 27 Mar 14
Last 20° Jun 23 Jun 8 May 29 May 20 May 11 May 3 Apr 24 Apr 14 Mar 30
Last 24° Jul 5 Jun 21 Jun 11 Jun 2 May 25 May 17 May 8 Apr 28 Apr 14
Last 28° Jul 10 Jun 29 Jun 20 Jun 13 Jun 7 May 31 May 24 May 15 May 4
Last 32° Jul 8 Jun 30 Jun 24 Jun 19 Jun 15 Jun 10 Jun 5 May 30 May 22
Last 36° Jul 8 Jul 2 Jun 28 Jun 25 Jun 21 Jun 18 Jun 14 Jun 10 Jun 4

ℹ️ How to read these charts for the fall

As summer ends in Grand Portage, MN, 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 August 7, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By August 26, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By September 15, 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 September 15 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° Oct 27 Oct 31 Nov 3 Nov 5 Nov 7 Nov 10 Nov 12 Nov 15 Nov 19
First 20° Oct 21 Oct 26 Oct 29 Nov 1 Nov 4 Nov 6 Nov 9 Nov 12 Nov 17
First 24° Aug 27 Sep 10 Sep 21 Sep 30 Oct 8 Oct 16 Oct 25 Nov 5 Nov 19
First 28° Aug 3 Aug 16 Aug 26 Sep 3 Sep 11 Sep 18 Sep 26 Oct 6 Oct 19
First 32° Jul 29 Aug 7 Aug 14 Aug 20 Aug 26 Sep 1 Sep 7 Sep 15 Sep 25
First 36° Jul 27 Aug 5 Aug 11 Aug 17 Aug 22 Aug 28 Sep 2 Sep 9 Sep 18

📍 Frost Dates for other nearby locations

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