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 6. 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 4, so we don't dare plant that early. We wait a few days and by May 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° | Feb 11 | Feb 2 | Jan 26 | Jan 20 | Jan 13 | Jan 2 | -- | -- | -- |
Last 20° | Feb 26 | Feb 14 | Feb 6 | Jan 29 | Jan 21 | Jan 14 | Jan 4 | Dec 21 | -- |
Last 24° | Mar 8 | Feb 27 | Feb 21 | Feb 16 | Feb 11 | Feb 6 | Feb 1 | Jan 26 | Jan 18 |
Last 28° | Apr 24 | Apr 15 | Apr 9 | Apr 4 | Mar 30 | Mar 25 | Mar 19 | Mar 13 | Mar 4 |
Last 32° | May 10 | May 3 | Apr 28 | Apr 24 | Apr 20 | Apr 16 | Apr 11 | Apr 6 | Mar 30 |
Last 36° | Jun 6 | May 30 | May 25 | May 21 | May 17 | May 13 | May 9 | May 4 | Apr 28 |
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 6 | Dec 20 | Dec 31 | Jan 11 | Jan 23 | Feb 9 | -- | -- | -- |
First 20° | Nov 20 | Dec 3 | Dec 12 | Dec 20 | Dec 27 | Jan 4 | Jan 14 | Jan 29 | -- |
First 24° | Oct 29 | Nov 9 | Nov 16 | Nov 23 | Nov 29 | Dec 5 | Dec 11 | Dec 19 | Dec 29 |
First 28° | Oct 17 | Oct 24 | Oct 30 | Nov 4 | Nov 9 | Nov 13 | Nov 18 | Nov 24 | Dec 1 |
First 32° | Sep 26 | Oct 3 | Oct 7 | Oct 11 | Oct 15 | Oct 19 | Oct 23 | Oct 27 | Nov 3 |
First 36° | Sep 9 | Sep 15 | Sep 20 | Sep 23 | Sep 27 | Sep 30 | Oct 4 | Oct 9 | Oct 15 |
Now that you know your frost dates, use our Garden Planting Calendar for Vancouver, 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.