Did you know you can tell the temperature by looking at the way the rhododendron leaves are curled? Rhododendrons are evergreens but that doesn't mean they love the cold weather. They can tolerate it but have learned to adjust by curling their leaves. The tighter the curl, the colder the temperature. These leaves are telling you it is under 20 F. Brrrrrrr... You can get lots more information here.