Plumeria Culture, A companion article to The Moragne Plumerias
Published April 01, 1991
While the Moragne hybrids are limited in availability outside of Hawaii, seeds, and cuttings of many other plumerias can be obtained through various mail-order catalogs and botanical gardens. Visitors to Hawaii often carry home cuttings of plumeria to remind them of their tropical vacations. The University of Hawaii receives many inquires about caring for these plants when they are taken to more northern climates.
It is important to remember that wild plumeria was found in hot, dry areas, often in poor soil, and on rocky limestone cliffs. While they respond readily to water and fertilizer, an overabundance of either tends to cause leggy growth with few flower clusters. Another problem with overwatering is the loss of roots due to the lack of air in the growing medium. For container culture, a well-drained medium is very important, and water should be applied only when the soil seems dry.
Plumeria growers in Hawaii often feed them year-round with a 10-30-10 fertilizer, believing that the extra phosphorous helps promote flower productivity. Recent research by horticulturists at the university has suggested that there is some validity to this practice, as trees fed with higher analysis phosphorus fertilizer had more growing points and slightly more flower clusters than trees given 10-10-10 or 10-20-10 fertilizer. Their rates of feeding were from one to four pounds of fertilizer per tree per year, based on tree size, and four applications (roughly a quarter pound of fertilizer per inch of trunk diameter up to four inches, spread under the drip line).
In northern areas with short growing seasons, the most important feedings will be the early and late ones. The spring feeding will help to develop the flower clusters and vegetative growth, while the late summer feeding, which should be low in nitrogen, will aid in setting the flower buds for the next year. Both organic and inorganic fertilizers are satisfactory.
In their native habitat, plumerias probably shed their leaves during a long dry spell, releafing when there is sufficient water. Regular and frequent deep irrigations promote long shoots. Thus, container culture is a balancing act between the grower’s goal of a perfect leafy, floriferous plant and the plumeria’s tendency to keep growing or to shed leaves and go dormant.
For good flowering, light and temperature are probably most important than water. The trees flourish in full sunlight and set few buds when shaded by taller trees or buildings. Very little growth or flowering occurs once the temperatures drop into the sixties and lower. Leaf retention, on the other hand, is more a matter of day length than temperature; growth decreases, too, as the days become shorter.
Plumeria fanciers in cold climates simply allow their plants to defoliate and go dormant in the fall. Then they bring them indoors, either bare-rooted or still in pots, and store them in a protected place-a garage, basement, or attic-where they won’t freeze. In March or April, they repot them if needed and once the danger of frost is past, they set the plants out to enjoy an early bloom. Growth and flowering are rapid with the return of temperatures to the seventies and eighties in spring and summer. They will grow and flower happily throughout the warm summer and fall months.
Those who want to attempt William Moragne’s method of cross-fertilizing plumeria will know within a month if they have a “take”; swellings should appear in two lobes at the base of the flower. The seed pods require six to nine months to mature, and eleven months to split open naturally.
Good seed is plump when squeezed lightly. Each has a little papery wing that enables seed dispersal by wind. If dried slightly and stored in good condition, they may remain viable for up to a year, but it is best to sow them immediately for a high germination percentage.
Seeds should be sown shallowly or stuck into the medium with the wind protruding. They should germinate in two to three weeks. Seedlings can be transplanted as soon as their stems have thickened and true leaves appear. Plumeria fanciers have observed flowering within a year, but more often it takes two to five years. For the last of his hybrid seedlings to bloom, William Moragne waited eighteen years.