The scientific name of the great rhododendron is Rhododendron maximum. It is commonly known as rose bay. This evergreen bush is related to the azalea. It can grow to be 5 to 40 feet tall, depending on how it is pruned. Great rhododendrons have twisty, woody stems that may form a thicket.
The bark of the great rhododendron starts as smooth, reddish brown. It is thin and breaks into scales as it ages. Stout branches start off yellowish-green with reddish brown hairs. As the branches age they turn rusty colored first then gray. As the branches age, they transition from soft and flexible to stiff.
Great rhododendron leaves start as scaly leaf buds on flowerless branches. They unfurl to be a 4- to 10-inch-long oval with rolled edges. They are shining bright green on top and dull-colored underneath. The evergreen leaves have a leathery texture. In winter, the stiff leaves tend to curl up.
Flower buds are large and conical. The buds open in June and display five-lobed, bell-shaped flowers that are 1½ inches across. The blossoms have hairy and spotted throats containing 8 to 12 curved stamens. Great rhododendron flowers are grouped together in clusters that are 5 to 8 inches across. Rose, purple and white flowers bloom until early summer.
Green capsules ½-inch long appear wherever a flower bloomed. These narrow fruits split along five lines and contain several seeds. The seeds are ejected in autumn, but the fruit hangs on to the branches all winter.
Great rhododendrons can be propagated through stem tip cuttings in the early summer. Cuttings grow roots in eight to 12 weeks when the soil temperature is 75 to 80 degrees F. Collect seeds in autumn and sow them in the spring. Germination takes six to eight weeks with daytime temperatures around 86 degrees F and nighttime temperatures of 68 degrees F.