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 15. 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. 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 20 | Mar 11 | Mar 3 | Feb 24 | Feb 17 | Feb 10 | Feb 1 | Jan 19 |
Last 20° | Apr 19 | Apr 8 | Mar 31 | Mar 24 | Mar 18 | Mar 11 | Mar 4 | Feb 25 | Feb 14 |
Last 24° | May 3 | Apr 24 | Apr 17 | Apr 12 | Apr 7 | Apr 2 | Mar 27 | Mar 21 | Mar 12 |
Last 28° | May 19 | May 11 | May 5 | Apr 30 | Apr 26 | Apr 21 | Apr 16 | Apr 11 | Apr 3 |
Last 32° | May 28 | May 22 | May 17 | May 12 | May 8 | May 4 | Apr 30 | Apr 25 | Apr 18 |
Last 36° | Jun 15 | Jun 7 | 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° | Nov 7 | Nov 13 | Nov 18 | Nov 22 | Nov 25 | Nov 29 | Dec 3 | Dec 8 | Dec 14 |
First 20° | Oct 25 | Oct 31 | Nov 4 | Nov 8 | Nov 11 | Nov 15 | Nov 18 | Nov 23 | Nov 29 |
First 24° | Oct 15 | Oct 21 | Oct 25 | Oct 29 | Nov 2 | Nov 5 | Nov 9 | Nov 14 | Nov 20 |
First 28° | Oct 5 | Oct 11 | Oct 16 | Oct 20 | Oct 23 | Oct 27 | Oct 31 | Nov 5 | Nov 11 |
First 32° | Sep 26 | Oct 2 | Oct 6 | Oct 9 | Oct 13 | Oct 16 | Oct 20 | Oct 24 | Oct 30 |
First 36° | Sep 19 | Sep 24 | Sep 27 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 13 | Oct 18 |
Now that you know your frost dates, use our Garden Planting Calendar for Holbrook, AZ 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.