The name Rhododendron comes from the greek words "rodon" which means "rose" and "dendron" which means "tree", hence Rose Tree. Rhododendron flowers are usually produced in trusses. The family Ericacea, into which the genus Rhododendron falls, also includes heathers, mountain laurels, blueberries and cranberries as well as manzanita, trailing arbutus, madrone, huckleberry, kalmiopsis, sourwood, blueberries and a number of other genus. Rhododendrons are referred to as the King of Shrubs since they are regarded by many as the best flowering evergreen plants for the temperate landscape.

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Rhododendron L.
  • Most people know rhododendrons as big leathery leafed shrubs with round clusters of white, pink, red, or purple blooms.
  • Rhododendron was discovered by The 16th century Flemish botanist, Charles l'Ecluse.
  • Rhododendron was introduced to Britain in 1656 from the European Alps, and so the name Alpine Rose for Rhododendron histrum.
  • Exploration in America came as a result of a partnership between English Quaker Peter Collinson and botanist/farmer John Bartram of Pennsylvania. This led to the importation to England of the American natives, Rhododendron canescens, Rhododendron nudiflorum, and Rhododendron viscosum in 1734, and Rhododendron maximum in 1736.
  • Rhododendron ferrugineum, another species from the European Alps also known as the Alpine Rose, came along in 1752.
  • The Washington State Senate confirmed that the Coast Rhododendron / Pacific Rhododendron (Rhododendron macrophyllum) would be the floral emblem for Washington state.
  • Rhododendron is also the national flower of Nepal, and the state flower of Sikkim in India.
  • All the parts of Rhododendrons are dangerous, especially leaves, showing symptoms of Stomach irritation, abdominal pain, abnormal heart rate and rhythm, convulsions, coma, death. Honey made from the nectar of Rhododendron flowers is also toxic and should not be consumed.
  • The genus Rhododendron includes both Rhododendrons and Azaleas. In this genus, both Rhododendron and Azalea are used as common names. The distinctions that follow are made by gardeners. The Rhododendron plants are usually evergreen and those labeled Azalea plants are deciduous, although there are a few evergreen Azaleas like those in the florist or nursery trade. To the typical gardener, azaleas are conspicuous because they don't have trusses. The exception to this is the Homebush type azaleas which have a very tight ball shaped truss but this type of azalea is deciduous. It should be mentioned that the tropical Vireya rhododendrons don't have a truss either and look more like azaleas but are in general treated as a special class, different from most other rhododendrons and azaleas.
  • Rhododendrons have ten or more stamens, while Azaleas have five.
  • Rhododendrons have large, paddle-shaped leaves and large, bell- or funnel-shaped flowers borne in terminal trusses. Azaleas have small, elliptical leaves and trumpet- or tubular-shaped flowers at the ends of the shoots. Still some rhododendrons, called lepidoes have small leaves and small flowers and some rhododendrons are naturally miniature have miniscule leaves and flowers. It is true that all azaleas have small leaves compared to the large leaved rhododendrons, the elepidotes.
  • Rhododendrons are erect, growing up to 80 feet high, while Azaleas are more twiggy, spreading bushes, usually reaching a height of no more than 8 feet.
  • Both Rhododendrons and Azaleas provide fragrant blossoms in an array of colors - from pure white and light pastels to brilliant orange and gold to purple and red. Some blossoms change color over time or are marked with contrasting colors.

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Never plant a rhododendron deeper than it was originally planted. The roots seldom ever extend more than twelve inches deep. Planting them deeper than twelve inches will prevent them from getting enough air.

  • Plant Rhododendrons in spring or fall.
  • Space plants 2 to 6 feet apart, depending on the expected mature size of the plant.Dig a hole only as deep as the root ball and 2 to 3 times as wide.
  • Rhododendrons need an acidic soil. If your soil is in very poor condition, amend the soil you've removed from the hole with a small amount of compost.
  • Carefully remove the plant from the container and set it in the hole.
  • Fill the hole half full with soil, then water it well to settle the soil and eliminate air pockets.
  • The chief killer of rhododendrons is wet soil. Rhododendrons need moist well drained soil, but not a water logged soil. Rhododendrons seem to thrive in Mediterranean climates where there are long periods with no rain.
  • Apply a layer of compost under the shrub each spring, spreading it out to the dripline (the area under the outermost branches).
  • Add a 2-inch layer of mulch to retain moisture and control weeds, keeping mulch a few inches away from the trunk.
  • Water plants during the summer if rainfall is less than 1 inch per week. In regions with severe winters, protect evergreen rhododendrons in the fall by wrapping burlap around them.
  • Although seldom, rhododendrons need Pruning to remove dead, damaged, or diseased branches anytime. Prune Rhododendrons to reduce height after flowering in spring. Rhododendrons will grow back from old wood.
  • Rhododendrons are not usually prone to insects or diseases. They can develop a condition called chlorosis, which is characterized by yellowing of a leaf between dark green veins. Chlorosis can be caused by malnutrition caused by alkalinity of the soil, potassium deficiency, calcium deficiency, iron deficiency or magnesium deficiency. A combination of acidification with sulfur and iron supplements such as chelated iron or iron sulfate will usually treat this problem. Chlorosis can also be caused by nitrogen toxicity (usually caused by nitrate fertilizers) or other conditions that damage the roots such as root rot, severe cutting of the roots, root weevils or root death caused by extreme amounts of fertilizer.