Landscape March 2014 L-23

Expanding Tree Diversity in Hawai‘i’s Landscapes: Na‘u, Nanu; Forest ; Gardenia brighamii

John Edward Montoya1, Richard Criley1, and Alberto Ricordi1 1Department of Tropical and Soil Sciences

he Hawaiian gardenia is one of three native garde- nia species and is federally listed as endangered. ItT is a small tree, up to 20 feet tall and 10–15 feet in diameter, with fragrant white flowers and attractive, glossy foliage. Being native to dry forest habitats, this beautiful, fragrant tree is an excellent choice for any landscape with relatively xeric conditions.

Recommended Use in Landscapes • Leeward side of all Hawaiian islands • Lower elevations with xeric conditions • Commercially and in residential areas as hedging, screening, to provide shade or accents, or used as a container plant

Distribution • Native to dry forests on all main Hawaiian islands but now extinct on Kaua‘i and extremely rare on the other islands • Elevation range: 1,000–2,000 feet • Precipitation range: 0–50 in.

Propagation Techniques • Propagated from seed, cutting, and air-layering • Germination can be expected in 1 to 8 months. • Cuttings can be slow to root, taking up to a year. Take cuttings from hard- and semi-hardwood material; use rooting powder No. 16. • Air layering is best done in spring or summer. Roots begin to appear after approximately 4 months; use rooting powder No. 16.

Published by the College of Tropical Agriculture and Human Resources (CTAHR) and issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in co- operation with the U.S. Department of Agriculture, under the Director/Dean, Cooperative Extension Service/CTAHR, University of Hawai‘i at Mānoa, Honolulu, Hawai‘i 96822. Copyright 2011, University of Hawai‘i. For reproduction and use permission, contact the CTAHR Office of Communication Services, ocs@ctahr..edu, 808-956-7036. The university is an equal opportunity/affirmative action institution providing programs and services to the people of Hawai‘i without regard to race, sex, gender identity and expression, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or status as a covered veteran. Find CTAHR publications at www.ctahr.hawaii.edu/freepubs. UH–CTAHR Expanding Tree Diversity in Hawai‘i’s Landscapes: Na‘u, Nanu L-23 — Mar. 2014

Cultural Requirements and Tolerance • Prune to develop tree form • Full sun and supplemental watering promote flowering • Water until established in landscape • Accepts arid conditions • Grows well in a wide range of well-drained soils • Drought and wind tolerant

Flower and Fruit Characteristics • Flowers are strongly fragrant (some say a slight smell of coconut). • Blooms sporadically year round. • Fruits are ping-pong ball sized.

Leaf Characteristics • Glossy, medium to dark green • Medium sized, simple, oval • Opposite arrangement • Thick with a smooth texture • Deciduous

Advantages for Use in Landscapes • Native • Long-lived (at least 15 years) • Thrives in full sun and partial shade • Requires little water • Minimum pruning required • No messy fruits • Fragrant flowers

Disadvantages for Use in Landscapes • Susceptible to ants, aphids, green coffee scale, black twig borer, thrips, mealybugs, and spider mites, but typically does not need treatment • Slow growing • Requires pruning to maintain tree form

Acknowledgements The authors thank Amanda Birnbaum for the many photographs she contributed to this publication.

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