When is it safe to plant?

When is it safe to plant my tender flowers and vegetables? That is a question we hear often at the garden center this time of year. It depends on where you live, of course, as higher elevations and more northern locales have a shorter growing season than lower elevations and more southern locales. And, of course, the weather can vary dramatically from year to year, so really what they are asking is, “What are the odds of getting a frost this time of year”.

Wall-o-waters in snow
Wall o’ Water Plant Protectors

As you can see in the charts below, if you wait until there is less than a 10% chance of a 32 degree frost, you will almost never dare plant. Most of us are willing to take more risk than that or we would never try to garden in east Idaho. Using the 50% chance of a 28 degree frost will lengthen your potential growing season dramatically. Just keep an eye on the weather and be prepared to throw a blanket over things in case of frost. Of course, you can always plant  up to 6 weeks early in Wall o’ Water plant protectors as they will protect into the upper teens.

All data is courtesy the National Climatic Data Center.

St Anthony, ID (Fremont county):

Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Spring 32° Jul 6 Jun 28 Jun 22 Jun 17 Jun 12 Jun 8 Jun 3 May 28 May 19
Spring 28° Jun 14 Jun 8 Jun 3 May 29 May 25 May 21 May 17 May 12 May 5
Spring 24° May 23 May 17 May 14 May 11 May 8 May 5 May 2 Apr 28 Apr 23
Fall 32° Aug 16 Aug 23 Aug 28 Sep 1 Sep 5 Sep 9 Sep 13 Sep 18 Sep 25
Fall 28° Sep 4 Sep 9 Sep 12 Sep 15 Sep 18 Sep 21 Sep 24 Sep 27 Oct 2
Fall 24° Sep 8 Sep 15 Sep 20 Sep 25 Sep 29 Oct 3 Oct 7 Oct 12 Oct 19

Idaho Falls 2 Ese, ID (Bonneville county):

Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Spring 32° Jun 16 Jun 9 Jun 4 May 31 May 27 May 23 May 19 May 14 May 7
Spring 28° May 24 May 18 May 14 May 11 May 7 May 4 May 1 Apr 26 Apr 21
Spring 24° May 5 Apr 30 Apr 26 Apr 23 Apr 20 Apr 17 Apr 14 Apr 10 Apr 5
Fall 32° Sep 7 Sep 11 Sep 15 Sep 17 Sep 20 Sep 22 Sep 25 Sep 28 Oct 2
Fall 28° Sep 19 Sep 23 Sep 26 Sep 29 Oct 2 Oct 4 Oct 7 Oct 10 Oct 14
Fall 24° Sep 26 Oct 2 Oct 6 Oct 9 Oct 12 Oct 15 Oct 19 Oct 23 Oct 28

Blackfoot 2 Ssw, ID (Bingham county):

Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Spring 32° Jun 15 Jun 9 Jun 5 Jun 1 May 28 May 25 May 21 May 16 May 10
Spring 28° May 23 May 17 May 13 May 9 May 6 May 3 Apr 29 Apr 25 Apr 19
Spring 24° May 7 May 1 Apr 27 Apr 24 Apr 21 Apr 18 Apr 15 Apr 11 Apr 5
Fall 32° Sep 2 Sep 8 Sep 11 Sep 15 Sep 18 Sep 21 Sep 24 Sep 28 Oct 4
Fall 28° Sep 15 Sep 20 Sep 24 Sep 28 Oct 1 Oct 4 Oct 7 Oct 11 Oct 16
Fall 24° Sep 23 Sep 29 Oct 3 Oct 7 Oct 10 Oct 14 Oct 18 Oct 22 Oct 28

American Falls 1 Sw, ID (Power county):

Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Spring 32° Jun 6 May 28 May 22 May 17 May 13 May 8 May 3 Apr 27 Apr 19
Spring 28° May 15 May 9 May 4 Apr 30 Apr 26 Apr 22 Apr 18 Apr 13 Apr 7
Spring 24° Apr 28 Apr 20 Apr 15 Apr 10 Apr 6 Apr 2 Mar 28 Mar 23 Mar 15
Fall 32° Sep 12 Sep 18 Sep 22 Sep 26 Sep 29 Oct 2 Oct 6 Oct 10 Oct 16
Fall 28° Sep 24 Sep 30 Oct 4 Oct 8 Oct 12 Oct 15 Oct 19 Oct 24 Oct 30
Fall 24° Oct 6 Oct 13 Oct 17 Oct 21 Oct 25 Oct 28 Oct 31 Nov 5 Nov 11

Grace, ID (Caribou county):

Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Spring 32° Jun 30 Jun 23 Jun 19 Jun 15 Jun 11 Jun 7 Jun 3 May 29 May 23
Spring 28° Jun 11 Jun 3 May 28 May 23 May 19 May 14 May 9 May 4 Apr 26
Spring 24° May 17 May 12 May 8 May 5 May 2 Apr 29 Apr 26 Apr 22 Apr 17
Fall 32° Aug 24 Aug 29 Sep 2 Sep 6 Sep 9 Sep 12 Sep 16 Sep 20 Sep 26
Fall 28° Sep 6 Sep 10 Sep 14 Sep 17 Sep 20 Sep 22 Sep 25 Sep 29 Oct 4
Fall 24° Sep 18 Sep 23 Sep 26 Sep 29 Oct 2 Oct 5 Oct 8 Oct 12 Oct 17

Alta 1 Nw, WY (Near Driggs, ID):

Temperature 10% 20% 30% 40% 50% 60% 70% 80% 90%
Spring 32° Jul 15 Jul 8 Jul 3 Jun 29 Jun 25 Jun 20 Jun 16 Jun 11 Jun 4
Spring 28° Jun 21 Jun 13 Jun 7 Jun 2 May 28 May 23 May 18 May 12 May 4
Spring 24° Jun 4 May 27 May 22 May 17 May 13 May 9 May 4 Apr 29 Apr 21
Fall 32° Aug 16 Aug 23 Aug 28 Sep 1 Sep 5 Sep 9 Sep 13 Sep 18 Sep 25
Fall 28° Sep 1 Sep 6 Sep 10 Sep 13 Sep 16 Sep 19 Sep 23 Sep 27 Oct 2
Fall 24° Sep 10 Sep 16 Sep 20 Sep 24 Sep 27 Sep 30 Oct 4 Oct 8 Oct 14

 

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