- Rhododendrons exhibit evergreen or deciduous foliage, depending on the species. Their shiny, oval-shaped, dark-green leaves have smooth margins and vary from 1/2 inch to 8 inches in length. Cultivated rhododendrons usually grow from 3 to 5 feet tall; wild varieties can grow as tall as 35 feet. They produce clusters of blossoms in shades of pink, orange, red, yellow, purple or white. Rounded seed capsules replace the flowers.
- Deciduous rhododendrons are generally more cold-hardy than the evergreen varieties. The Northern Lights azalea hybrids, which are a cross between Rhododendron prinophyllum and Rhododendron x kosteranum, can survive at temperatures below minus 40 degrees F. These cultivars grow to about 6 feet tall. 'Knapp Hill' hybrids are popular garden plants, according to the University of Missouri Extension; they produce pink, orange, cream or yellow flowers. Several evergreen rhododendron cultivars include 'Everestianum,' which yields pinkish-purple blossoms; 'America,' a variety that produces rounded clusters of dark-red blossoms; and 'P.J.M.' hybrids, with its pink or lavender blossoms and small evergreen leaves.
- Rhododendrons prefer humid climates with moderate temperatures and require well-drained acidic soil with a pH level between 4.0 and 5.5. You can add ferrous sulfate, acid peat or sulfur to neutral or alkaline soil to increase the soil's acidity level. Rhododendrons grow best in shady locations and require protection from harsh sunlight. They also have shallow root systems and need frequent watering during the summer. Rhododendrons benefit from an organic mulch to prevent the growth of weeds and retain soil moisture. Plant rhododendrons near buildings or on slopes to protect them from wind damage.
- Mice, deer and rabbits feed on rhododendron shrubs during the winter. Black vine weevils feed on the leaf margins; their larvae feed on its roots. Severely infested plants suffer stunted growth and may eventually wither and die. Rhododendrons planted in poorly drained soil may suffer from phytophthora root rot, also known as rhododendron wilt; diseased roots become mushy and rotten and plants die quickly. Rhododendrons are also susceptible to winter burn, which causes brown, dried leaves, and iron deficiency from incorrect pH levels.
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