About

Nerium oleander, the oleander, is a shrub or small tree native to the Mediterranean region east to southern Asia, from Morocco and Portugal east to India and Myanmar; the Flora of China also cites it as native in Yunnan in China. It is the only species currently classified in the genus Nerium, belonging to subfamily Apocynoideae of the dogbane family Apocynaceae. It is also cultivated widely in temperate and subtropical areas as an introduced ornamental and landscaping plant.

It is tolerant to both drought and inundation, but not to prolonged frost. It is a highly poisonous plant but its bitterness renders it unpalatable to humans and most animals, so poisoning cases are rare and the general risk for human mortality is low. Ingestion of larger amounts may cause nausea, vomiting, excess salivation, abdominal pain, bloody diarrhoea and irregular heart rhythm.

How to grow it

Beyond the traditional Mediterranean and subtropical range of oleander, the plant can also be cultivated in mild oceanic climates with the appropriate precautions. It is grown without protection in warmer areas in Switzerland, southern and western Germany and southern England and can reach great sizes in London and to a lesser extent in Paris due to the urban heat island effect. This is also the case with North American cities in the Pacific Northwest like Portland, Seattle, and Vancouver. Plants may suffer damage or die back in such marginal climates during severe winter cold but will rebound from the roots.

On the East Coast of the United States, it grows as far north as Virginia Beach, while in California and Texas miles of oleander shrubs are planted on median strips. There are estimated to be 25 million oleanders planted along highways and roadsides throughout the state of California. Because of its durability, oleander was planted prolifically on Galveston Island in Texas after the disastrous Hurricane of 1900.

Safety

Oleander is a poisonous plant—containing the toxic steroidal aglycone, cardenolide-type cardiac glycosides, odorosiside, adigoside, and oleandrin,—especially when consumed in large amounts. These compounds have a narrow therapeutic index and are toxic when ingested. Adverse effects after ingestion include weakness, diarrhoea, nausea, vomiting, headache, stomach pain, and death.

Toxicity studies of animals have concluded that birds and rodents are relatively insensitive to oleander cardiac glycosides. However, other mammals such as dogs and humans, are relatively sensitive to the effects of cardiac glycosides and they typically present clinical manifestations of "glycoside intoxication".

Where it grows

Nerium oleander is either native or naturalised to a broad area from northwest Africa through the Mediterranean region and warmer areas of the Black Sea region, Arabian Peninsula, southern Asia, and as far east as Yunnan in southern parts of China. It can be found in tropical, subtropical, and temperate regions. The plant typically occurs in dry locations with a lot of sun near stream beds where it can alternatively tolerate long seasons of drought and inundation from winter rains.