Laura Dean Bennett
Rhododendron watchers may have noticed that there seems to be a lot of what botanists would call, “organic yellowing” going on with their leaves this fall.
Maybe because their leathery leaves look nothing like what we might think of as evergreen foliage, it’s odd to think of them as evergreen. But they are.
And even evergreens, such as pine and spruce trees, shed some of their needles each fall. Sometimes they drop a few and sometimes they lose a large number of needles.
Shortly before winter, a healthy, mature rhododendron (two to three years old) will have a certain amount of foliage turn yellow and die off.
Not to worry. This is a normal stage of its life cycle and is nothing to be concerned about.
Of course, like any plant, organic yellowing can also occur when the plant is stressed because it’s trying to grow in a location that’s too wet or too dry, has too much sun or it lacks proper nutrients.
Rhododendrons are a genus of more than 1,000 species of flowering plants native to Europe, Asia and North America.
The name Rhododendron comes from the Greek words rhodos, meaning rose, and dendron, meaning tree. They are part of the Ericaceae family, which includes blueberries, cranberries, mountain laurel and azaleas.
Azaleas are close relatives of the rhododendron. All azaleas are rhododendrons, but not all rhododendrons are azaleas.
There are more than 800 species of rhododendron ranging from spreading ground covers a few inches high to 100-foot tall trees. Twenty-four species of rhododendron are native to North America.
Along with azaleas, there are more than 200 hybrid species of this incredible plant, which is one of the most popular plants in the world.
Most of the rhododendron we see here in Pocahontas County is Rhododendron maximum, which is common throughout eastern North America.
Its common names include great rhododendron, American rhododendron and great laurel.
Rhododendron is actually a flowering shrub, or small tree. It produces magnificent blooms of pink, white, purple or red in late spring or early summer and the blooms can last for several weeks.
Another close relative of rhododendron is mountain laurel. They are sometimes confused with each other, the difference mainly being that everything about mountain laurel is smaller than rhododendron.
Mountain laurel’s height is two-to-three feet as opposed to 10-to-20 feet for rhododendron. Leaf length is three-to-four inches compared to four-to-six inches, and mountain laurel has smaller blossoms, too, although their blossoms are similarly colored.
Both grow wild in Pocahontas County.
Rhododendron maximum beat out honeysuckle and wild roses in a poll of West Virginia public school children and was designated the official state flower of West Virginia in 1903.
Rhododendrons are be-loved all over the United States. They are the most popular woody landscape plant in the country, probably because of their spectacular, colorful blooms and their hardy disposition.
All rhododendrons love shade, especially during the hottest part of the day.
They do best if they have morning sun and afternoon shade, or dappled sunlight throughout the day.
Too much sun can scorch the leaves and too little sun can make the plants leggy.
If you have rhododendrons, or pass them on the road on a regular basis, you will have noticed one of their most interesting features – the way their leaves curl up in response to the cold.
Like living thermometers – they curl and uncurl in response to temperature changes.
Many desert plants also have this ability, as do tulips and crocus, which close up at night or on cold, rainy days.
When temperatures are above 40 degrees Fahrenheit Rhododendron leaves are flat, collecting sunlight a lot like solar panels. As the temperature drops to 32 degrees, they begin to droop and curl up.
It’s believed that a lack of water in the stem causes this. Curling starts in earnest when temperatures dip down to 25 degrees. If the temperature drops below 20 degrees, rhododendron leaves are curled up tight.
Their leathery texture protects the leaves, but even so, they would be completely frozen at 18 degrees Fahrenheit. To protect frozen leaf cells from the damage which would occur during a rapid thaw, rhododendron developed the ability to curl its leaves.
As less surface area is exposed to the sun, the ice crystals in the curled leaves thaw more slowly and leaf cell membranes remain intact.
Snow can act as an insulator. If there is a layer of snow on their leaves, they will curl less, or not at all.
It is a fascinating fact that rhododendron leaf curling can occur whether or not the leaf is attached to the plant. Try this experiment: bring a curled leaf inside and see how fast it opens up.
Their leaves regulate their water intake and are designed to release water quickly. To avoid dehydration, they may need to be watered during excessive heat, dry or windy weather and sometimes even in the winter months.
In the correct climate, in a predominantly shady area and in well-drained acidic soil, a rhododendron can live for decades, even up to 100 years. The oldest known rhododendron is estimated to be 131 years old.
Rhododendrons can be carefully pruned to encourage additional growth and more robust blooms. This should be done during the fall, when leaf yellowing is underway.
There is so much to recommend rhododendron as a brilliant addition to almost any landscape. It is as lovely as it is rugged.
With or without their gorgeous blooms, they are showy and adaptable in almost all seasons.
During the summer, blooming rhododendrons provide a glorious show beside their deciduous neighbors in the shady woods.
Later in the year, even in sub-zero weather, their foliage provides a contrast of color – from green to silver-gray – against the spartan winter landscape.
However, as beautiful as they are, it should be noted that, while not all are equally toxic, almost all rhododendron is poisonous to humans, pets and livestock. Ingesting any part of the plant, especially in large quantities, can be potentially fatal.