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 3. 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 6, so we don't dare plant that early. We wait a few days and by June 17 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 26 | Apr 19 | Apr 14 | Apr 10 | Apr 6 | Apr 2 | Mar 29 | Mar 24 | Mar 17 |
| Last 20° | May 11 | May 6 | May 2 | Apr 28 | Apr 25 | Apr 22 | Apr 19 | Apr 15 | Apr 9 |
| Last 24° | May 23 | May 18 | May 15 | May 12 | May 9 | May 6 | May 3 | Apr 29 | Apr 24 |
| Last 28° | Jun 10 | Jun 4 | May 31 | May 28 | May 24 | May 21 | May 17 | May 13 | May 8 |
| Last 32° | Jun 25 | Jun 19 | Jun 15 | Jun 12 | Jun 8 | Jun 5 | Jun 1 | May 28 | May 22 |
| Last 36° | Jul 3 | Jun 27 | Jun 23 | Jun 20 | Jun 17 | Jun 14 | Jun 10 | Jun 6 | Jun 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° | Oct 18 | Oct 22 | Oct 26 | Oct 28 | Oct 31 | Nov 3 | Nov 6 | Nov 9 | Nov 14 |
| First 20° | Sep 29 | Oct 5 | Oct 10 | Oct 13 | Oct 17 | Oct 20 | Oct 24 | Oct 29 | Nov 4 |
| First 24° | Sep 20 | Sep 25 | Sep 29 | Oct 2 | Oct 5 | Oct 8 | Oct 12 | Oct 15 | Oct 21 |
| First 28° | Sep 12 | Sep 17 | Sep 20 | Sep 22 | Sep 25 | Sep 27 | Sep 30 | Oct 3 | Oct 7 |
| First 32° | Sep 6 | Sep 10 | Sep 13 | Sep 15 | Sep 17 | Sep 19 | Sep 22 | Sep 24 | Sep 28 |
| First 36° | Aug 22 | Aug 27 | Aug 31 | Sep 4 | Sep 7 | Sep 10 | Sep 13 | Sep 17 | Sep 22 |
Now that you know your frost dates, use our Garden Planting Calendar for Circleville, 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.
The Victory Seed Company is family owned and operated, working to help fellow gardeners succeed by selling popular vegetable, herb and flower seeds. Since the 1990s they have been heavily involved with the preservation of rare, open-pollinated, heirloom seeds. Visit them at www.VictorySeeds.com.
