Frost Dates: First and last frost dates for Boise Lucky Peak Dam, ID

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 13, 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° Mar 3 Feb 23 Feb 17 Feb 12 Feb 8 Feb 3 Jan 29 Jan 23 Jan 15
Last 20° Mar 24 Mar 16 Mar 9 Mar 4 Feb 27 Feb 23 Feb 17 Feb 11 Feb 3
Last 24° Apr 22 Apr 12 Apr 4 Mar 29 Mar 23 Mar 18 Mar 12 Mar 4 Feb 22
Last 28° Apr 30 Apr 24 Apr 19 Apr 16 Apr 12 Apr 9 Apr 5 Apr 1 Mar 26
Last 32° May 22 May 16 May 12 May 8 May 5 May 1 Apr 28 Apr 23 Apr 17
Last 36° Jun 13 Jun 7 Jun 3 May 30 May 27 May 24 May 20 May 16 May 10

ℹ️ How to read these charts for the fall

As summer ends in Boise Lucky Peak Dam, ID, 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 28, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By October 8, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By October 18, 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 18 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 7 Nov 15 Nov 21 Nov 26 Nov 30 Dec 5 Dec 10 Dec 16 Dec 24
First 20° Oct 21 Oct 29 Nov 4 Nov 9 Nov 14 Nov 19 Nov 24 Nov 30 Dec 9
First 24° Oct 15 Oct 22 Oct 27 Oct 31 Nov 4 Nov 8 Nov 12 Nov 16 Nov 23
First 28° Oct 8 Oct 14 Oct 18 Oct 21 Oct 24 Oct 28 Oct 31 Nov 4 Nov 10
First 32° Sep 23 Sep 28 Oct 2 Oct 5 Oct 8 Oct 11 Oct 14 Oct 18 Oct 23
First 36° Sep 10 Sep 15 Sep 19 Sep 22 Sep 26 Sep 29 Oct 2 Oct 6 Oct 11

📍 Frost Dates for other nearby locations

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