Oleander

Identification and origin

Nerium oleander belongs to the Apocynaceae, the dogbane family. Its native range runs around the Mediterranean, from Spain and Morocco to Greece and Turkey, then across the Middle East and the Arabian Peninsula to Afghanistan, Pakistan, India and Myanmar. There it grows in streambeds that dry out in summer. Today it is naturalized in many warm regions of the world. The epithet oleander refers to the olive (Olea), whose leaves its own resemble.

It is a rounded, fast-growing evergreen shrub. Its narrow, linear-lanceolate leaves are 4–7 in long and less than 1 in wide; they are opposite or in whorls of three or four, with a prominent midrib. The five-petaled flowers, 1–2 in across and often fragrant, are clustered at the branch tips; they come in pink, white, red, purple, salmon or pale yellow, single or double. The fruits are long pods that split open along one side.

In the ground in mild climates it reaches 5–19.5 ft tall. In containers it usually stays at 4–8 ft. Dwarf cultivars of 2–4 ft exist, such as ‘Petite Pink’ (pale pink) and ‘Petite Salmon’. Popular cultivars include ‘Calypso’ (single, cherry red, very hardy), ‘Hardy Pink’ (better cold tolerance), ‘Sister Agnes’ (pure white), ‘Mrs. Roeding’ (double pink) and ‘Variegatum’, with variegated leaves.

Light

Full sun is essential for good flowering. In part shade the plant stretches, becomes leggy and blooms little. On a balcony or patio, choose the sunniest spot, ideally south-facing and sheltered from wind. While overwintering it needs at least moderate light; a cool, very bright room suits it even better.

Watering

Once established in the ground, oleander is remarkably drought tolerant: it slows down without showing visible damage. In a container the water supply is limited: water regularly during growth and bloom, but let the mix dry out between waterings. Push a finger into the soil: as long as it still feels moist, wait.

While overwintering in a cool spot, the plant uses almost no water: water very sparingly, just enough to keep the root ball from drying out completely.

Potting mix

In the ground, oleander adapts to clay, loam, sand or rocky soil, acidic or alkaline, even poor soil. It also tolerates salt spray and brackish water, which makes it an excellent coastal shrub.

In containers it does best in fertile, well-drained soil: use a peat-free, loam-based mix in a pot with good drainage holes. In the ground, a single feeding a year is enough.

Temperature

Oleander is grown in the ground in USDA zones 8a to 10b. Temperatures at or below 32 °F can damage it. A container plant tolerates some light frost; you can leave it outdoors in fall as long as the thermometer stays above 23 °F, then move it back out as soon as spring weather allows. A short overwintering period suits it best.

For winter there are two options: a cool spot at about 39–48 °F with moderate light and very little water, or a cool, sunny room with reduced watering. In a sunroom or greenhouse, ventilate well.

Repotting

Grow it in a large, well-drained container filled with a fertile, loam-based mix. A plant that has outgrown its winter shelter is better kept in check by pruning than by moving it into ever larger containers. Oleander can also be trained as a standard: a rounded head on a short trunk is common in nurseries and suits containers well.

Whenever you handle it, wear gloves and long sleeves: the sap can irritate some people’s skin.

Pruning

At the end of winter, remove dead wood and branches damaged by frost. Light pruning after flowering, from late summer into fall, improves the shape. Flowers form on the current season’s growth: do not prune after early fall, or you will remove next year’s buds. Under glass, restrictive pruning is done in late winter; the plant tolerates hard pruning if it becomes too large.

Pull out suckers at the base while they are young: they divert the plant’s energy and reduce flowering. Deadhead spent flowers to prevent seed pods. Never burn the prunings: the smoke is toxic.

Propagation

Stem cuttings are one of the recommended methods. Take semi-hardwood cuttings in summer from current-season shoots whose base is starting to firm up; cuttings taken in late summer root well. Air layering, which roots a branch while it is still attached to the parent plant, is done in spring.

Seed is also possible. Wear gloves at every step, because the sap is irritating.

Common problems

• Few flowers: not enough sun, pruning too late that removed the flowering shoots, or too many suckers at the base.
• Dead or damaged branches at winter’s end: frost damage; remove them.
• Scale and mealybugs: waxy clusters or small shells on stems and leaf undersides, often with sooty mold, a black coating that grows on the honeydew.
• Aphids on young shoots, and spider mites under glass.
• Caterpillars: in warm regions where it occurs, the oleander caterpillar can strip a plant in one or two weeks.
• Leaf spot: remove and destroy affected leaves.
• Decline: Armillaria root rot, less often. Oleander is also a high-risk host of the bacterium Xylella fastidiosa: bring in only healthy plants.

A single symptom can have several causes: always consider light, watering, cold exposure and pests together.

Toxicity

Oleander is highly toxic to people as well as to dogs, cats and horses. All parts, fresh or dried, contain cardiac glycosides, including nerioside and oleandroside. Ingestion causes nausea, vomiting, abdominal pain, sometimes bloody diarrhea, dizziness, slowed pulse or irregular heartbeat, dilated pupils and drowsiness, and can be fatal; chewing a leaf or twig once or twice can be enough to send a person to the hospital. In animals, signs include drooling, abdominal pain, diarrhea, colic and depression.

Smoke from burning plant material is also dangerous, and the sap can cause skin reactions. Plant it away from play areas and animals, wear gloves when handling it and, in case of ingestion, contact a poison control center or a veterinarian immediately.