Monday, February 15, 2010

Thermotropism in Plants

How cold is it outside this morning? Look out the window....perhaps your rhododendron is telling you.
On very cold winter mornings some broadleaf evergreen shrubs, like rhododendron and daphniphyllum in my landscape, droop down and/or curl up. (see photo). This is a specific response by some plants to sub-freezing temperatures, called “thermotropism”.
Scientists do not fully understand the cause of this foliar response. It may have something to do with leaf cell hydration. Thermotropism also may protect leaves during periods of high irradiance by sunlight. It may protect from cold temperature injury during daily thawing and re-freezing inside the leaf of some broadleaf evergreens.
On most days, leaves unfurl to their full natural position by late morning as temps rise above 32 °F (0 °C). Remember to water evergreen shrubs every 2-3 weeks if natural rainfall and snowfall are more than 60% below seasonal averages.


  1. Nice! Now I understand more about what plants do in cold days. The only thing is that what about homeostasis?

  2. is there a hormone responsible for this?