Frost Dates: First and last frost dates for Swan Falls P H, 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 May 26, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around May 6, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before April 23, 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 6 Feb 22 Feb 13 Feb 5 Jan 30 Jan 23 Jan 15 Jan 7 Dec 26
Last 20° Mar 17 Mar 7 Feb 28 Feb 21 Feb 16 Feb 10 Feb 4 Jan 28 Jan 18
Last 24° Mar 30 Mar 20 Mar 13 Mar 7 Mar 1 Feb 24 Feb 18 Feb 11 Feb 1
Last 28° Apr 23 Apr 14 Apr 8 Apr 3 Mar 29 Mar 24 Mar 18 Mar 12 Mar 3
Last 32° May 20 May 10 May 3 Apr 27 Apr 21 Apr 15 Apr 9 Apr 2 Mar 23
Last 36° May 26 May 19 May 14 May 10 May 6 May 2 Apr 28 Apr 23 Apr 17

ℹ️ How to read these charts for the fall

As summer ends in Swan Falls P H, 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 October 9, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By October 20, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By October 30, 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 30 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 17 Nov 27 Dec 4 Dec 10 Dec 16 Dec 22 Dec 28 Jan 5 Jan 17
First 20° Nov 8 Nov 15 Nov 20 Nov 25 Nov 29 Dec 3 Dec 8 Dec 13 Dec 22
First 24° Oct 24 Nov 1 Nov 6 Nov 11 Nov 15 Nov 20 Nov 24 Nov 30 Dec 7
First 28° Oct 11 Oct 19 Oct 24 Oct 28 Nov 1 Nov 5 Nov 10 Nov 15 Nov 22
First 32° Oct 3 Oct 9 Oct 13 Oct 16 Oct 20 Oct 23 Oct 26 Oct 30 Nov 5
First 36° Sep 21 Sep 27 Oct 1 Oct 4 Oct 8 Oct 11 Oct 15 Oct 19 Oct 24

📍 Frost Dates for other nearby locations

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