Plumeria trees normally lose their leaves and go dormant in response to short days, so plumeria growers have very few blossoms to sell during the winter.

Treatment with ethephon, a chemical used to ripen fruit, stimulates plumeria flowers to develop early, providing blossoms for winter lei.

Normally, plumeria trees lose their leaves and go dormant as the autumn days grow shorter. The flower buds that start to form during the long days of summer do not appear until the midwinter days warm and lengthen. CTAHR horticulturist Richard Criley has found that ethephon, a chemical used by the pineapple industry to stimulate flowering and ripen fruits uniformly, can induce plumeria trees to flower early, producing blossoms for the winter tourist season.

When ethephon is applied to a plumeria tree in September or October, it breaks down to form a non-toxic gas that causes the leaves to fall from the tree. Leaves are the “eyes” of a plant—the organs that allow it to perceive light—so a leafless, ethephon-treated plumeria tree is unable to sense the shortening day lengths and fails to go dormant. If the nights are warm enough, generally above 65°F, the plant begins to regrow. Not all shoots yield flower buds in response to treatment, but enough flowers are produced to harvest for lei. The common yellow plumeria popular with commercial growers responds well to ethephon, and the resulting winter flowers equal spring blossoms in size and quality. The treatment does not prevent spring flowering, since buds continue to push out even after the initial flush of bloom.

The timing of the ethephon treatment is important. Apply it too early, and only flower stalks are produced, not flowers. Apply it too late, and flower production misses the peak visitor arrival period. Couple a well-timed application with mild nighttime temperatures, though, and growers can overcome plumeria’s tendency to take the winter off, giving vacationers a hint of year-round summer.

For more information about Hawaii’s plumeria, you can download the free publication Plumeria in Hawaii . A more in-depth treatment of lei flowers and foliage is offered in Growing plants for Hawaiian lei -- 85 plants for gardens, conservation, and business . For questions about the research discussed in this story, please contact Dr. Richard Criley at criley@hawaii.edu.