Frost Dates: First and last frost dates for Sisters, OR

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 August 2, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around July 23, there's a 50/50 chance of frost — check weather forecasts carefully if planting now
  • Before July 17, 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 1 Apr 20 Apr 12 Apr 5 Mar 30 Mar 24 Mar 17 Mar 9 Feb 26
Last 20° May 20 May 13 May 7 May 3 Apr 28 Apr 24 Apr 19 Apr 13 Apr 6
Last 24° Jun 18 Jun 10 Jun 4 May 30 May 25 May 20 May 15 May 9 May 1
Last 28° Jul 18 Jul 10 Jul 4 Jun 28 Jun 24 Jun 19 Jun 13 Jun 7 May 30
Last 32° Jul 31 Jul 24 Jul 20 Jul 16 Jul 12 Jul 8 Jul 4 Jun 30 Jun 23
Last 36° Aug 2 Jul 29 Jul 27 Jul 25 Jul 23 Jul 21 Jul 19 Jul 17 Jul 13

ℹ️ How to read these charts for the fall

As summer ends in Sisters, OR, 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 17, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By August 27, 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 August 27 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 4 Oct 12 Oct 19 Oct 24 Oct 29 Nov 3 Nov 8 Nov 15 Nov 23
First 20° Sep 24 Sep 30 Oct 4 Oct 8 Oct 11 Oct 15 Oct 19 Oct 23 Oct 29
First 24° Sep 4 Sep 10 Sep 15 Sep 19 Sep 23 Sep 27 Oct 1 Oct 5 Oct 12
First 28° Aug 19 Aug 25 Aug 29 Sep 1 Sep 4 Sep 7 Sep 11 Sep 15 Sep 20
First 32° Aug 2 Aug 7 Aug 11 Aug 14 Aug 17 Aug 20 Aug 24 Aug 27 Sep 2
First 36° Jul 29 Aug 1 Aug 4 Aug 7 Aug 9 Aug 12 Aug 15 Aug 18 Aug 22

📍 Frost Dates for other nearby locations

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