I have a very large rhododendron “bush” outside my kitchen door by my patio. It was here when I moved in 12 years ago and has gotten so tall I can see it out my upstairs bathroom window. It is a beautiful thing, especially when it blooms in May. I am lucky enough to have one in front of my house by my garage, too.
Some days during the winter I look out my window and it looks like this:
I was pretty freaked out the first time I saw this – I was afraid I had neglected to cover it, to protect it from the cold. But after doing some research I found that this phenomenon is called a “thermotropic” reaction and is a natural reaction that helps prevent dehydration under conditions of extreme stress.
In this photo it is covered with snow but it’s not cold enough for the leaves to curl. However they are drooping.
It’s a very accurate temperature indicator, so when I look outside and the leaves look like this, as they do today (18 degrees!), I say “D**n, it’s cold!”