What's a safe temperature for tender plants? When the nightly temperature falls, frost can form, even above 32°, because the air is colder high above the ground and the frost can form up there and then fall down onto your garden and do some damage, even if it's 36° on the ground. So many factors come into play, including wind, concrete, houses, trees and other structures, etc etc etc. Because of all this, you might want to consider 36° as "the danger zone".
In your average springtime, you have a 90% chance that there will be no 36° nights by June 28. In other words, you can pretty much count on being safe from frost by that day. But we want to get those tomatoes in the ground as soon as possible, right? We see that there's still an 80% chance of 36° on May 31, so we don't dare plant that early. We wait a few days and by June 11 we are at the 50/50 point. At this point, we are close and we can start watching the weather forecast. If the upcoming week's forecast doesn't show below 40°, then it's probably okay to risk planting out your plants. If conditions change and a surprise frost does threaten, there's always things you can do to protect plants from frost.
Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
---|---|---|---|---|---|---|---|---|---|
Last 16° | Apr 10 | Apr 2 | Mar 27 | Mar 22 | Mar 18 | Mar 13 | Mar 8 | Mar 3 | Feb 23 |
Last 20° | Apr 22 | Apr 15 | Apr 11 | Apr 7 | Apr 3 | Mar 30 | Mar 26 | Mar 22 | Mar 15 |
Last 24° | May 5 | Apr 30 | Apr 26 | Apr 23 | Apr 20 | Apr 17 | Apr 14 | Apr 10 | Apr 5 |
Last 28° | May 24 | May 18 | May 14 | May 11 | May 7 | May 4 | May 1 | Apr 26 | Apr 21 |
Last 32° | Jun 16 | Jun 9 | Jun 4 | May 31 | May 27 | May 23 | May 19 | May 14 | May 7 |
Last 36° | Jun 28 | Jun 22 | Jun 18 | Jun 14 | Jun 11 | Jun 7 | Jun 4 | May 31 | May 25 |
The charts on this page show the probabilities of receiving a certain temperature on a certain day. Some examples that might help:
Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
---|---|---|---|---|---|---|---|---|---|
First 16° | Oct 21 | Oct 27 | Oct 31 | Nov 4 | Nov 7 | Nov 11 | Nov 14 | Nov 19 | Nov 24 |
First 20° | Oct 7 | Oct 14 | Oct 18 | Oct 22 | Oct 26 | Oct 30 | Nov 2 | Nov 7 | Nov 13 |
First 24° | Sep 26 | Oct 2 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 19 | Oct 23 | Oct 28 |
First 28° | Sep 19 | Sep 23 | Sep 26 | Sep 29 | Oct 2 | Oct 4 | Oct 7 | Oct 10 | Oct 14 |
First 32° | Sep 7 | Sep 11 | Sep 15 | Sep 17 | Sep 20 | Sep 22 | Sep 25 | Sep 28 | Oct 2 |
First 36° | Aug 26 | Aug 31 | Sep 3 | Sep 6 | Sep 9 | Sep 12 | Sep 15 | Sep 18 | Sep 23 |
Now that you know your frost dates, use our Garden Planting Calendar for Idaho Falls, ID to know when to sow and transplant your various vegetable plants!
Data is provided by the NOAA National Centers for Environmental Information. Photography by Garden.org member TBGDN.