Frost Dates: First and last frost dates for Prospect, 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 July 16, you have a 90% chance of being frost-free — this is your "safe date" for planting tender crops
  • Around June 24, 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° Mar 1 Feb 15 Feb 4 Jan 25 Jan 16 Jan 6 Dec 25 Dec 8 --
Last 20° Mar 18 Mar 4 Feb 23 Feb 14 Feb 7 Jan 30 Jan 21 Jan 11 Dec 26
Last 24° Apr 22 Apr 10 Apr 2 Mar 26 Mar 19 Mar 13 Mar 6 Feb 25 Feb 14
Last 28° May 26 May 18 May 12 May 8 May 3 Apr 28 Apr 23 Apr 18 Apr 10
Last 32° Jun 19 Jun 13 Jun 8 Jun 4 May 31 May 27 May 23 May 18 May 12
Last 36° Jul 16 Jul 8 Jul 3 Jun 28 Jun 24 Jun 20 Jun 15 Jun 10 Jun 2

ℹ️ How to read these charts for the fall

As summer ends in Prospect, 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 September 14, there's a 20% chance of 32°F — start monitoring forecasts and have plant covers ready
2
Decision time: By September 25, there's a 50% chance of frost — harvest tomatoes, peppers, and other tender crops or prepare protection
3
Last chance: By October 7, 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 7 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 Dec 2 Dec 13 Dec 23 Jan 1 Jan 12 Jan 25 Feb 18 --
First 20° Nov 9 Nov 20 Nov 28 Dec 4 Dec 11 Dec 17 Dec 24 Jan 1 Jan 15
First 24° Oct 25 Nov 3 Nov 10 Nov 16 Nov 22 Nov 28 Dec 4 Dec 11 Dec 21
First 28° Sep 25 Oct 2 Oct 7 Oct 12 Oct 16 Oct 20 Oct 25 Oct 30 Nov 7
First 32° Sep 8 Sep 14 Sep 18 Sep 22 Sep 25 Sep 29 Oct 2 Oct 7 Oct 13
First 36° Aug 14 Aug 22 Aug 27 Aug 31 Sep 4 Sep 9 Sep 13 Sep 18 Sep 25

📍 Frost Dates for other nearby locations

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