Driving along Central Valley freeways in the spring and summer, I can’t help but notice the oleanders with their beautiful, vibrant colors and grey-green foliage. Oleanders (Nerium oleander) are native or naturalized to a broad area of the earth, where they can alternatively tolerate long seasons of drought and heavy winter rains. In California, miles of these shrubs are planted on median strips. There are estimated to be 25 million oleanders planted along highways and roadsides throughout California.
The name oleander is mentioned as far back as the first century when a Greek physician cited the shrubs as being used by Romans. Because of its durability, oleanders were planted on Galveston Island, Texas, after a hurricane in 1900. Now, Moody Gardens in Galveston hosts the propagation program for the International Oleander Society. New varieties are hybridized and grown on the grounds, a repository for every named variety.
Oleander has formed the subject matter of paintings by famous artists including: Gustav Klimt, who painted “Two Girls with an Oleander” and Vincent van Gogh, who painted his famous “Oleanders” in Arles in 1888.
The oleander shrub is easy to identify. Look for its eight- to 10-inch long lance-shaped, leathery leaves, growing opposite each other on long stems. Leaves are light green and very glossy when young, and become a dull dark grayish green as they mature. The flowers grow in clusters at the end of each branch, one to two inches in diameter, often sweet-scented. The fruit is a long narrow pair of pods, splitting open at maturity to release numerous downy seeds. The shrub is evergreen and can be from five to 20 feet tall at maturity.
Over 400 cultivars have been named, with several flower colors, including white, pink, red, yellow, peach and salmon. Some cultivars are multi-colored, others are double flowered, with large, rose-like blooms and strong fragrance. Several dwarf cultivars have also been developed, offering a more compact form and size for small spaces.
In our area, oleander is a vigorous grower, extensively used as an ornamental plant in parks, along roadsides and in private gardens. It is most commonly grown in its natural shrub form, but can be trained into a small tree with a single trunk. Oleanders bloom from April through October, with the heaviest bloom usually occurring between May and June.
The plant is tolerant of poor soils, intense heat, salt spray, sustained drought, and light frost, making it perfect for our area of high summer temperatures, low rainfall, and relative frost-free winters. As with many drought tolerant plants, it will flower and grow more vigorously with regular water. Although it does not require pruning to thrive and bloom, oleanders can become unruly with age and older branches tend to become gangly. For this reason, gardeners are advised to prune mature shrubs in the autumn to shape and induce lush new growth and flowering for the following spring. Oleanders are relatively disease and pest resistant.
Now, a word of warning. The name oleander most likely comes from a Greek word, meaning “I kill.” Oleanders have historically been considered poisonous plants, especially to humans and animals. The leaves and stems are toxic due to the presence of multiple alkaloids (particularly oleandrin). Poisonings have occurred in animals on farms and dairies from eating dried leaves discarded over fences to feed livestock. It has been estimated that three leaves are enough to kill a horse or cow. Also, dogs chewing sticks from the plant can become intoxicated and die. If you have a young active chewing dog, having this plant in your yard is not a good choice.
Human cases have occurred with people using the straight stalks of oleander to roast marshmallows or hot dogs. Symptoms usually occur several hours after ingesting a toxic dose, and may include dizziness, abdominal pain, and diarrhea. But, don’t let the toxins in the plant worry you unduly. Oleander poisonings in humans are rare. Keep things in perspective —most poisonings in California are due to carbon monoxide. The most commonly ingested poisons for children under six are everyday household products; such as cosmetics, cleaning substances, and pain relievers. Watch young children and pets around oleanders, making sure they do not have access to any parts of the plants.
In the event of suspected ingestion of any part of the oleander plant, contact your doctor, the California Poison Control System, 1-800-222-1222, or 911.
As long as people are aware of its toxicity, oleander is a good choice for certain areas in our gardens because of its versatility, drought resistance, hardiness, and long-blooming beauty.
Due to the shelter-at-home guidelines, the Master Gardeners have canceled all public events for the time being, but their phone lines are still open: 559-684-3325, Tuesdays and Thursdays between 9:30 and 11:30 a.m. Or visit their web site at ucanr.edu/sites/UC_Master_Gardeners.