The oleander (Nerium oleander) is a popular, hardy flowering shrub known for its dense foliage and prolific, long-lasting blooms. Originating in the Mediterranean and parts of Asia, this plant thrives in warm climates. Its resilience to heat, drought, and poor soil conditions makes it a favored choice for landscaping and a relatively low-maintenance option for gardeners.
Essential Environmental Needs
Oleanders require a location receiving full sun for optimal flower production, needing a minimum of six to eight hours of direct sunlight daily. Insufficient light can cause the plant to become lanky with fewer, less vibrant flowers. While tolerant of various conditions, the oleander thrives best in well-draining soil, ideally within a slightly acidic to neutral pH range of 6.0 to 7.5.
The plant is susceptible to root rot if left in standing water or consistently soggy soil, making good drainage essential. If planting in heavy clay, amending the soil with organic matter or sand will improve drainage. Once established in the ground, the oleander is drought-tolerant, reflecting its arid native habitat.
Newly planted oleanders need consistent moisture to develop a strong root system, requiring deep watering two to three times per week for the first few months. For established plants, watering should be reduced, allowing the soil to dry out between applications. Container-grown oleanders typically need more frequent watering than those planted in the landscape.
Routine Seasonal Maintenance
Feeding supports robust growth and continuous flowering throughout the growing season. For in-ground plants, a light application of a balanced, slow-release granular fertilizer in early spring is sufficient. Container-grown plants lose nutrients more quickly and benefit from a more frequent feeding schedule, such as an all-purpose granular fertilizer applied every four to six weeks.
Pruning maintains shape, encourages branching, and promotes flowering, as oleanders bloom on new growth. Major pruning is best done immediately after the peak bloom period in late summer or early fall, or in late winter/early spring before new growth begins. Removing spent flower clusters (deadheading) helps stimulate subsequent flushes of blooms.
For shaping, make cuts just above a leaf node with three leaves to encourage bushier growth. Renewal cuts, which remove up to one-third of the oldest stems down to the ground, can rejuvenate an overgrown plant every three to five years. Avoid severe pruning in late fall, as the resulting tender new growth is susceptible to frost damage.
Troubleshooting and Protection
Oleanders can be affected by pests such as the oleander aphid, scale, and mealybugs. Oleander aphids are bright yellow sap-suckers that congregate on new growth and excrete honeydew. This sticky residue often leads to the growth of sooty mold, a black fungus that coats leaves and impedes photosynthesis.
Scale insects appear as small, hard-shelled or cottony bumps on stems and leaves, feeding on sap and weakening the plant. Infestations of these sucking pests can be managed using horticultural oil or insecticidal soap. Apply treatments particularly during the plant’s dormant season or when pests are first observed.
Oleanders tolerate light frost, surviving temperatures down to 15 to 20 degrees Fahrenheit, but they are not fully cold-hardy. In marginal climates, in-ground plants benefit from a thick layer of organic mulch, such as wood chips or straw, applied around the base to insulate the root zone. Container-grown oleanders should be moved to a protected location, like an unheated garage, when temperatures consistently drop below 40 degrees Fahrenheit.
Safety Warning Regarding Toxicity
Every part of the Nerium oleander plant, including the leaves, flowers, stems, and sap, contains potent cardiac glycosides, making it highly poisonous if ingested by humans, pets, or livestock. The toxicity remains even when dried, and smoke from burning oleander debris is also toxic.
Symptoms of poisoning include severe gastrointestinal distress, followed by serious effects on the circulatory system, such as an irregular heart rate, low blood pressure, collapse, or death. Wear protective gloves when handling the plant, especially during pruning, to prevent skin irritation from the sap. Clippings must be disposed of safely and never burned.