Fall is quickly giving
way to winter, if temperature is any indication. Each morning as I walk
from front door to car door, my breath condenses in the cold air to become
visible. In the warmth of summer days, such a fundamental aspect of being
alive is rarely considered, but here, in the cold, I feel like a child
who has witnessed a bit of magic—my breath transformed into a visible cloud,
if only briefly.
As I look around
me, the evidence of cold is visible elsewhere, too. Judging from the rhododendrons,
it must be about 30 degrees. I check the thermometer, and am not far off—it’s
28.
The leaves of rhododendrons respond to cold
by first drooping, then curling up. At temperatures above freezing, the
leaves extend at approximate right angles from the stems.
Rhodendron at 40 degrees F
Just below freezing, the leaves droop downwards,
but remain flattened.
Rhododendron at 28 degrees F
At 25 degrees, or thereabouts, the leaves
droop and curl, and by 20 degrees, they are curled so tightly that they
look like green pencils.
Rhododendron at 23 degrees F
Once the temperature drops below 20, they
can’t curl up much tighter, and only a non-living thermometer will do.
The leaves curl because
they lose water, just as many other plants wilt. Severe droughts also cause
rhododendron leaves to droop and curl. The pores through which the plant
loses water and takes up air are located on the underside of the leaves.
When the leaves curl, these pores are protected, and the evaporation of
additional water is reduced. The curled leaves protect the rhododendron
plant from more water loss.
There are several species
of rhododendrons, only some of which retain their leaves in winter. The
most common is Rhododendron maximum, the rosebay or great-laurel.
It is widely distributed in the Appalachians, from New England south to
Georgia, and is common at low elevations. Deciduous species of rhododendrons
drop their leaves during fall. They are the flame azaleas, among others.
Rhododendrons, azaleas,
blueberries, mountain laurel, dog hobble, sourwood, trailing arbutus, wintergreen,
indian pipe, and many other common plants belong to the Heath family of
plants. This family grows well on the acidic soils of the Appalachians
and prefers the cold winters we experience. They are adapted also to droughts,
by virtue of their leaf curling ability. Most of these plants do equally
well as ornamental varieties and hybrids, but the native species are just
as beautiful.
Rhododendrons grow profusely
along stream banks and in hardwood forests, where they can form a thicket
so dense that it is difficult to walk through. Known as “heath hells” and
other equally picturesque names, countless hikers, hunters, and botanists
have bemoaned the jungle-gym obstacle course they present. Only the sourwoods
grow to tree size; the other heaths are shrubs or understory plants. The
rosebay rhododendron reaches a maximum height of 30 feet, but is rarely
more than 15 feet tall. Ancient rhodies can reach a foot in diameter, but
most are much smaller. These smaller shrubs are commonly used in crafts
and rustic furniture.
Heaths occur in other
parts of the world, too, and one of the best known is the heather that
blankets the Scottish Highlands. The beautiful patchwork of greens, blues,
and burgundies almost certainly contributed to the famous scotch plaids
by which the different clans are identified. Among the heather, those plaids
may also have been effective camouflage. Like so many other artisans, the
Scots took their inspiration from the natural world around them.
Next time you encounter
a rhododendron, estimate the temperature by evaluating the curl of its
leaves. You may surprise yourself with the plant’s accuracy.
copyright 2001 by Jennifer
E. Frick
please do not use images or
text without permission
