Oleander is a large flowering shrub or small tree that makes an effective screen or attractive specimen plant. From late spring through fall, fragrant white, yellow, pink or red single or double flowers cover this easy-care perennial. Oleander grows quickly, eventually reaching 10 to 20 feet tall and 10 to 12 feet wide.
Oleander requires temperatures above -6.67 degrees Celsius to grow well. The shrub can survive temperatures down to -9.44 to -6.66C, but foliar damage occurs. Temperatures below -15C kill the plant. Frost-damaged oleanders recover quickly in the spring, if the roots sustained no damage.
Plant oleander in a full-sun location that receives reflected heat from a south- or west-facing wall. The plant grows in partial shade but becomes leggy and produces few flowers. Oleander tolerates just about any soil type, as long as it is well-drained.
Watering and Feeding
Although oleander is drought tolerant and requires little water once established, the plant does best with a monthly soaking during the spring and summer months. Oleander tolerates overhead watering and salt spray. While oleander grows satisfactorily without fertilising, the plant grows more vigorously if fed with an all-purpose fertiliser every two months.
Oleander allowed to grow naturally forms a large mound. The plant tolerates hard pruning to control its size and shape its form. Before spring growth begins, cut the oleander's oldest stems to the ground and prevent bushiness at the base of the plant by pulling up suckers. Severely cut back especially rangy plants in early spring before new growth begins. Encourage rapid re-blooming throughout the season by removing dead flower clusters promptly.
Oleander is susceptible to pests such as the oleander caterpillar, a 2-inch-long orange-red, hairy black insect that feeds on leaves and can defoliate a plant within a few days. Leaf loss won't kill oleander, but it does weaken the plant and can make it more prone to other pests such as scale insects, aphids and mealybugs. Effective treatment for the oleander caterpillar is Bacillus thuringiensis (Bt) variety kurstaki. Other pests can be controlled with horticultural oils and insecticidal soaps.
Diseases that attack oleander include Botryosphaeria dieback. Caused by a fungus, this condition causes branches and shoots to die back and blacken. It is especially prevalent in plants that have experienced drought stress or freeze damage. Cut out all infected plant parts. Leaf scorch is a serious bacterial disease caused by the glassy-winged sharpshooter. Infected plants brown and die quickly, and there is no known cure. Cutting out infected plant parts seems to slow the progress of the disease.
All oleander plant parts are extremely toxic. Children have been poisoned by leaves and twigs. The plant's sap causes skin inflammation. Avoid burning pruned plant parts, as the smoke causes severe irritation to the lungs.