Have you ever wondered why the leaves of your rhododendrons curl up in very cold weather? You may observe that the leaves on your plants are drooping down and curling up. Is something wrong with these plants?
Do not panic. What you are observing is the plant protecting itself. They practice thermotropism. Thermotropism or thermotropic movement is the movement of a plant or part of a plant in response to a change in temperature.
Normally, rhododendron leaves are flat and extend horizontally from the plant, but in the winter, the leaves of some rhododendrons will droop, and they might curl around as if the leaf is giving itself a big hug. Much like when humans wrap their arms around themselves or animals huddle when cold, rolling up their leaves offers protection from cold winds. The inner part of the leaf, where a lot of moisture loss occurs, is hidden from the wind when rolled.
Gardeners claim they can tell the temperature by how their rhododendron leaves appear; the more they roll and droop, the colder it is, until around zero they start to look like green beans hanging from the branches. As it warms again, the leaves unroll and stand up again.
