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 29. 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 29, so we don't dare plant that early. We wait a few days and by June 10 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 16 | Apr 9 | Apr 4 | Mar 31 | Mar 27 | Mar 23 | Mar 18 | Mar 13 | Mar 6 |
Last 20° | May 3 | Apr 27 | Apr 22 | Apr 18 | Apr 14 | Apr 10 | Apr 6 | Apr 1 | Mar 25 |
Last 24° | May 10 | May 4 | Apr 30 | Apr 26 | Apr 23 | Apr 20 | Apr 16 | Apr 12 | Apr 6 |
Last 28° | May 24 | May 19 | May 15 | May 12 | May 9 | May 7 | May 4 | Apr 30 | Apr 25 |
Last 32° | Jun 9 | Jun 3 | May 30 | May 27 | May 23 | May 20 | May 16 | May 12 | May 6 |
Last 36° | Jun 29 | Jun 23 | Jun 18 | Jun 14 | Jun 10 | Jun 6 | Jun 2 | May 29 | May 22 |
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 25 | Oct 30 | Nov 2 | Nov 5 | Nov 8 | Nov 10 | Nov 13 | Nov 17 | Nov 21 |
First 20° | Oct 15 | Oct 20 | Oct 24 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 7 | Nov 12 |
First 24° | Oct 1 | Oct 7 | Oct 11 | Oct 15 | Oct 18 | Oct 22 | Oct 25 | Oct 30 | Nov 4 |
First 28° | Sep 19 | Sep 24 | Sep 27 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 17 |
First 32° | Sep 10 | Sep 14 | Sep 18 | Sep 21 | Sep 24 | Sep 26 | Sep 29 | Oct 3 | Oct 8 |
First 36° | Aug 31 | Sep 5 | Sep 9 | Sep 12 | Sep 15 | Sep 18 | Sep 21 | Sep 25 | Sep 30 |
Now that you know your frost dates, use our Garden Planting Calendar for Morgan Power & Light, UT 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.