Revised by Joey Williamson, HGIC Hortculture ExtensionAgent, Clemson University, 03/16. Originally prepared by Karen Russ, HGIC Information Specialist, and Bob Polomski, Extension Consumer Horticulturist, Clemson University. New 07/01. Images added 05/09, 01/13, & 10/15
Oleanders (Nerium oleander) are distinctive and beautiful large, flowering shrubs that thrive with little care. They are very heat and drought-tolerant once established, and will grow especially well in seaside gardens, tolerating salt spray and wind. Oleanders generally grow best in the coastal areas of South Carolina. Most cultivars will be damaged or killed by winter cold in the Midlands and Piedmont.
Flowers and buds of a double-flowered, white oleander (Nerium oleander).
Karen Russ, ©2008 HGIC, Clemson Extension
Most cultivars will grow to 8 to 12 feet tall and almost as wide as they are tall. In some protected areas mature plants may reach up to 20 feet tall. Some dwarf cultivars stay as low as 3 to 5 feet.
Oleanders grow at a medium to rapid pace, producing 1 to 2 feet or more of growth per year. Established plants that have been damaged by cold will regrow very quickly from the base.
Oleanders are usually very large, mounded shrubs that take up considerable space in the landscape. Their quick growth rate and thick multi-stemmed habit makes them ideal for use as a screen or informal hedge.
Oleanders flower from early summer until mid-autumn with large clusters of 2-inch single or double blossoms. Colors range from pure white through pale-yellow, peach, salmon and pink to deep burgundy red. Some varieties (mostly doubles) are fragrant.
Flowers and buds of a single-flowered, light pink oleander (Nerium oleander).
Joey Williamson, ©2013 HGIC, Clemson Extension
The leaves are smooth, dark green, thick and leathery. They are long and narrow, usually between 4 and 6 inches long and an inch or less wide. The dwarf cultivars also have smaller leaves. Leaves generally grow in whorls.
Oleander (Nerium oleander) leaves and branch habit.
Karen Russ, ©2008 HGIC, Clemson Extension
Oleanders grow best in full sun and will tolerate even reflected heat from a south or west wall. They will tolerate partial shade, but may have a lanky, open shape.
Oleanders are tolerant of many different soil types, but must have good drainage. They will not do well in wet areas. Oleanders are very drought-tolerant once established, but respond well to occasional deep watering.
Oleanders can be allowed to grow in their natural large mound form, or they can be trained to a small multi-stemmed tree. Since oleanders bloom in summer on new growth, prune them in the early spring. Oleanders will tolerate quite hard spring pruning to remove cold damaged or overgrown wood. Remove dead flower clusters to encourage longer bloom. Cut stem tips off to encourage branching after the flowers are spent, but avoid cutting too late in the fall, as the new growth may not have enough time to harden before frost.
Most oleanders will survive temperatures down to 15 to 20 °F, although their foliage will be damaged. They are typically listed for growing in USDA zones 8b to 10. Even on the coast some winter damage may occur each year. If the tops are killed back by cold, they will recover quickly in spring as long as the roots were not damaged.
Oleander is extremely poisonous*. Eating even small amounts of any part of the plant can make a person or animal severely ill or cause death. Contact of sap with skin may cause irritation. Smoke from burning cuttings can cause severe reactions.
Cold injury on Oleander (Nerium oleander) foliage. New growth has begun in early April.
Joey Williamson, ©2015 HGIC, Clemson Extension
Botryosphaeria dieback, caused by the fungus Botryosphaeria species causes branches and shoots to die and turn blackish brown. The disease is more likely to occur when plants have been subjected to drought stress or damaged by severe freezes. Prune out all affected branches, making sure that no discolored tissue is left in the cross section.
Oleander caterpillars are the most damaging pest of oleanders.
Anne W. Gideon, www.insectimages.org
The oleander caterpillar is the most damaging pest of oleanders. Young oleander caterpillars feed in groups, skeletonizing young shoots. Mature caterpillars are highly visible - up to 2 inches long, orange-red with black tufts of hair. A severe infestation can strip a plant bare of leaves in a few days. While even total defoliation will not kill an established plant, it will weaken it, and may make it more susceptible to other pests. Aphids, mealybugs and scales may also occasionally be problems.
In general, cultivars with thicker, dark green, leathery leaves tend to be hardier to cold. Single flowers usually drop cleanly while spent double flowers may linger unattractively on the plant. On the other hand, most fragrant oleanders have double flowers. Nurseries often sell oleanders by color rather than by name.
*Acute Cardiac Toxicity of Nerium indicum (Oleander) Poisoning. Khan, I. et al. Heart Views, (2010). Oct-Dec. 11(3), 115–116. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3089829/
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