Did you know you can tell the temperature by looking at your rhododendron leaves?
Different species and hybrids curl their leaves at varying temperatures.
Emma Erler, host of Homegrown NH and lead horticulturist with Kirkwood Gardens, says if you pay attention to your thermometer and the temperature at which the leaves on your rhododendron start to curl, you may develop the ability to determine how cold it is outside just by looking at your plant.
To reduce desiccation and winter injury, rhododendrons change their leaf angle and curl to limit water stress. Curled and drooping leaves are less exposed to both the wind and sun, which results in less water loss.
“The roots cannot draw enough water from the frozen soil to make up for the water that is lost through their leaves by transpiration,” Erler says.
In general, this is nothing to worry about, Erler says, especially if you have a hardy species or hybrid such as Rhododendron P.J.M. or Rosebay rhododendron (Rhododendron maximum).
Once the temperatures rise above the freezing mark again, the leaves should uncurl and perk up.
But if your plant does suffer some winter injury, wait to prune until spring when new growth has started, and it is easier to assess the damage to the branches.
Even if a branch looks completely lifeless, it’s possible that dormant buds will break in late spring.
Wait to prune until new leaves are emerging, which may not be until late May or early June.
See you in the garden!
Homegrown New Hampshire is a collaboration between Squam Lakes Natural Science Center and NHPR.
