How the Oleander Attracts Pollinators

Flowers and Seeds

• Oleanders do not produce nectar; they lack the requisite nectar-producing disks to do so. The oleander plant’s showy, hermaphroditic flowers have five free lobes, long tubes and pink corollas. The flower pollen is a sticky aggregate; consequently, a single pollination can fertilize many ovules within a single pollination. Each fruit will contain approximately 180 hairy, water-dispersed seeds. Seeds are frequently shed during the rainy season. Germination into oleander seedlings is fairly rapid; however, seed survival rates tend to be low.

Pollinator Attraction

• Medium-sized oleanders, approximately 6 feet tall and wide, can produce more than 100 inflorescences a year. Each inflorescence will have between three and five lateral branches that can produce between 12 and 40 individual flowers. During peak bloom, as many as 17 individual flowers per inflorescence may open at any one time. Due to the sheer quantity of blooms, oleanders are highly visible to pollinators from far distances.

Pollinators

• An oleander pollinator must be equipped with an extended proboscis, like a butterfly or moth. The oleander hawk moth, in particular, is one of the most important oleander pollinators. As a moth withdraws its tongue, which can get jammed in the narrow spaces among the anther filaments, some of the oleander's sticky pollen will cling to its proboscis. The moth will then transfer this pollen to the next flower.

Pollination Rates

• While oleanders are technically fully self-compatible, automatic self-pollination is prevented by the spatial distance between the anthers and stigmas. Within one study, published by the Botanical Journal of the Linnean Society, only eight insect visits to oleanders were observed over a two-year span. Fruit set of open-pollinated flowers is similarly low. Hand pollination will increase pollination rates in the short run, but it will cause the pods from ovaries pollinated later in the season to abort prematurely.