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How Cold is It?

February 10, 2012

How do you know when it’s cold? Like, really cold?

When the rhododendron’s leaves are curled.

curled rhododendron leaves

This is more fun than looking at my thermometer.

rhododendron full

It was 23-degrees Fahrenheit when I took these photos. The leaves open up when the sun warms them.

Here’s a little bit of reading on this thermotropic phenomenon. Interestingly, it’s an indicator of  leaf temperature, not the air temperature. A good explanation for why the leaves relax in sunlight, despite the persistence of low air temperature.

Do you pay attention to rhododendron leaf curling? What other plant phenomenon do you find interesting?

2 Comments leave one →
  1. Rebekah permalink
    January 20, 2013 8:48 pm

    Hello! My 8th grade son is doing a science fair experiment on Rhododendron leaf curl. Thank you for your site and the information. Would you be willing for us to post your photo on his display board? Thank you for your time!

  2. January 21, 2013 12:50 am

    Sure, happy to help. Sounds like an interesting project!


    Sent from my iPhone

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