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