On cold winter days, you may notice the leaves of rhododendrons and some other broad-leaf evergreens curling up around the edges. But this doesn’t mean the plants are wilting—wilting is a response to a lack of water. Rather, rhododendron leaves curl in response to cold temperatures, a reaction that is called a thermotropism.
Thermotropic leaf-curling is likely an adaptation that helps to protect the leaves from cold, but researchers are still investigating to better understand exactly how rhododendrons make this movement and how it benefits them. You can see plenty of examples of rhododendrons with curled leaves in the Japanese Hill-and-Pond Garden on cold days. Revisit same plant on warmer day, and you will see their leaves safely unfurled.
