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 16. 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 9, so we don't dare plant that early. We wait a few days and by May 24 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.
Temperature | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
---|---|---|---|---|---|---|---|---|---|
Last 16° | Feb 3 | Jan 21 | Jan 8 | Dec 24 | -- | -- | -- | -- | -- |
Last 20° | Feb 18 | Feb 5 | Jan 27 | Jan 18 | Jan 10 | Dec 31 | Dec 16 | -- | -- |
Last 24° | Feb 28 | Feb 18 | Feb 12 | Feb 6 | Jan 31 | Jan 26 | Jan 20 | Jan 12 | Jan 1 |
Last 28° | Apr 22 | Apr 9 | Mar 30 | Mar 22 | Mar 14 | Mar 7 | Feb 27 | Feb 17 | Feb 4 |
Last 32° | May 21 | May 13 | May 8 | May 3 | Apr 29 | Apr 24 | Apr 19 | Apr 14 | Apr 6 |
Last 36° | Jun 16 | Jun 8 | Jun 2 | May 28 | May 24 | May 19 | May 14 | May 9 | May 1 |
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° | Dec 14 | Dec 28 | Jan 10 | Jan 27 | -- | -- | -- | -- | -- |
First 20° | Nov 24 | Dec 9 | Dec 19 | Dec 29 | Jan 8 | Jan 19 | Feb 5 | -- | -- |
First 24° | Nov 14 | Nov 24 | Nov 30 | Dec 6 | Dec 11 | Dec 17 | Dec 22 | Dec 30 | Jan 10 |
First 28° | Oct 26 | Nov 4 | Nov 11 | Nov 16 | Nov 22 | Nov 27 | Dec 2 | Dec 9 | Dec 18 |
First 32° | Oct 7 | Oct 13 | Oct 18 | Oct 22 | Oct 26 | Oct 30 | Nov 3 | Nov 8 | Nov 14 |
First 36° | Sep 18 | Sep 25 | Sep 30 | Oct 4 | Oct 8 | Oct 12 | Oct 16 | Oct 21 | Oct 27 |
Data is provided by the NOAA National Centers for Environmental Information.