The other side is that we don't want to prune frozen plants and crush a frozen cambium cell layer. This will leave a jagged edge that will not heal as quickly and may become infected with a bacteria. This is true with all plants ranging from trees to roses. If it froze last night but warmed up to above freeing by ten in the morning, you are probably safe by two o'clock to prune. You will be able to see the bad cut if it is still frozen.
Another thing to consider is that walking on frozen turf grass, as you prune your shrubs, will shatter the stem and often damage the grass. This will show the following spring.
The good thing about Idaho weather is it never last forever...so we stop in this weather and be ready for the next warm up. There's three months to work with so we just have to be patient.
