How cold has it been in Boston lately? Cold enough for the rhododendron leaves to begin to curl. And, cold enough for some of our readers to dig out a post from 2008 to learn about it. So, here's a bit of that readers' choice for those of you who have discovered BostonZest, in more recent times.
Rhododendrons can be used as a natural thermometer, if you learn the signals their leaves are giving you.
This photo (above) was taken mid-winter as the leaves were beginning to tighten into their most protective roll.
Garth Wedemire over at The Amercian Rhododendron Society says, "Leaves of rhododendrons respond to cold by first drooping…then curling up.
- At temperatures above freezing, the leaves extend at approximately right angles from the stems.
- Just below freezing, the leaves droop downwards…but remain flattened.
At 25° or thereabouts…the leaves droop and curl, and by 20°, they are curled so tightly that they look like green pencils. Once the temperature drops below 20°, they can't curl up much tighter, and only a non-living thermometer will do."
Here's the page with Garth Wedemire's article.
Here's what the leaves look like when it is under 20 degrees.
He says this is a defensive reaction designed to prevent moisture loss from the leaves. These plants will show some drooping and curling in extreme heat as well.
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Words: Penny Cherubino
Photography: © 2008 and © 2013 Penny Cherubino
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