As long as freeways have been getting landscaped, oleanders have been contributing their profuse white, pink and red bloom. Heat, exposure and lack of moisture do not seem to bother them. They have become less common recently only because of new diseases that had never before been problematic. The diseases do not necessarily kill all oleanders everywhere, but are serious problems where the nurseries that grow most oleander are located.
The largest oleanders can get more than fifteen feet tall, and can be pruned up as small trees with multiple trunks. Oleander trees with single trunks almost never stand up straight, and do not want to give up their stakes. Because flower clusters develop at the ends of new growth, frequent exterior pruning or shearing inhibits bloom. Dwarf cultivars that are naturally proportionate to their space will bloom better than larger types that need to be pruned for confinement.
Oleander flowers are about an inch or two wide, with five petals, although some have ruffly ‘double’ flowers. Unfortunately, double flowers tend to hang on as they deteriorate after bloom. Some oleanders are slightly fragrant. The name ‘oleander’ is derived from the similarity of their leaves to those of olive trees (‘Olea‘), although oleander leaves can get three times as long.