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