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