Now that the weather has turned mighty cold, you may notice something strange happening to your Rhododendrons. The leaves on your plants are drooping down and curling up. Is something wrong with these plants?
You are seeing nature at its best. It’s cold, and when certain broadleaved evergreens get cold, they take measures to protect themselves. They practice thermotropism. Much like a human wraps their arms around themselves or animals huddle when cold, rolling up their leaves offers these 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. That is, unless it’s gotten so cold they have dried out completely and died, which can happen even with the hardiest rhododendrons. Moisture loss is what causes most winter injury in plants.
If you want your rhododendrons to look like this in the spring, you'll want to protect them from the winter elements.
Treating your broadleaved evergreens an antitranspirant in fall will help. This water based product seals the leaves and stems so that moisture is not released from them. It’s something to remember for next fall.
Also remember to plant broadleaved evergreens in areas protected from north winds to help prevent leaf desiccation and plant loss.
If you'd like to learn more about tree and plant health, take advantage of a free consultation with a Carpenter Costin arborist.