Winter has hit the Valley (and much of the rest of the country) with a vengeance this week. Thanks to a deep trough in the jet stream, bitter cold air has funneled down from Canada and invaded as far south as the Gulf States. Time for us to bundle up in our hats and gloves and warm winter coats! I guess that’s one way to get us in the holiday spirit!
Interestingly enough, plants have their own way of coping with the cold weather. Take Rhododendron for instance – just ’cause I think this is really cool! These broad-leaved evergreens have always intrigued me with their temperature-sensitive leaf movements. In cold hardy species of Rhododendron, the thick, evergreen leaves begin to droop and curl as the temperature approaches freezing, and the colder the temperature, the tighter they curl and the more they droop.
My mom first taught me about this when I was little growing up in New Jersey. We had a lot of beautiful rhododendrons planted in our yard and we always thought it was neat the way the leaves curled up tight and hung down like little green cigars in the winter.
There are several different theories as to why this leaf curling and drooping occurs in rhododendrons but there is no debate that it is temperature related. Many researchers feel that it is a way to protect the leaves from desiccation due to freezing temperatures and drying winter winds. Others believe that it protects delicate cell membranes from damage caused by rapid thawing following a freeze. Their theory is that the curled leaves hanging vertically thaw much slower than flat leaves held horizontally and this protects the cells from freeze damage.
Regardless of the reason, I’m happy just to know that they curl when it’s cold and leave it at that because, as it turns out, you can use the degree of “curl” in the leaf to estimate the outside air temperature – a “rhododendron thermometer”!
I have my very own “rhododendron thermometer” right outside my bedroom window. Every morning when I wake up in the winter, I can get an idea of how cold it is just by looking out the window at my rhododendron.
- If the leaves are curled really tight, I know it’s really cold out, at least 20°F or even colder. That’s how they’ve been this past week! Brrrrr!
- If they are curled just a little, I know it’s not super cold out, maybe just around 30 degrees or so.
- When the temperature is around 40°F or so, the rhododendron leaves just droop a little but are not curled; they don’t usually begin to curl until the temperature drops close to freezing.
- When it’s nice and warm out, the leaves are flat and held horizontally to capture the sun’s rays.
Just some fun plant trivia that might come in handy someday!
Until next time –
Happy Gardening and check your “rhododendron thermometer”!