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Hibiscus arnottianus

Hawaiian white hibiscus

Malvaceae Oahu and Molokai, Hawaiian Islands

Attracts Pollinators Attracts Butterflies Fragrant (light)Container Friendly

SunFull Sun – Part Shade

WaterMedium

HardinessZones 9–11

Overview

Hibiscus arnottianus is an evergreen shrub to small tree 6-30 feet (2-9 m) tall and 6-15 feet (1.8-4.5 m) wide, with smooth gray bark and an upright, open framework. Leaves are ovate to elliptic, 2-6 inches (5-15 cm) long, glossy dark green, with red-tinged veins and petioles and a smooth or shallowly toothed margin. Flowers are white, 4-6 inches (10-15 cm) across, with five broad petals and a staminal column 3-5 inches (7.5-12.5 cm) long that is usually pink to red and projects well past the petal tips. The flowers carry a light scent, a trait absent from most Hibiscus spp. species, which is why this plant appears in the parentage of many scented modern hibiscus hybrids. Each flower opens at dawn and closes by evening, and plants flower through the year with a spring peak. Three subspecies are recognised: subsp. arnottianus spp. in the Waianae Range of Oahu, subsp. punaluuensis spp. in the Koolau Range, and subsp. immaculatus spp. on Molokai, which carries a white staminal column and is listed as endangered. Plants live 10-20 years, and Chinese rose beetle and aphids feed heavily on soft growth in humid gardens.

Native Range

Hibiscus arnottianus is endemic to the Hawaiian Islands and occurs naturally only on Oahu and Molokai. It grows in mesic and wet forest and on gulch slopes between 1,000 and 3,300 feet (300-1,000 m), where annual rainfall runs 60-150 inches (1,500-3,800 mm). Subspecies immaculatus spp. is confined to a small area of northern Molokai.

Suggested Uses

Grown as a specimen shrub, informal hedge, and screen in Hawaiian and subtropical gardens at spacings of 8-10 feet (2.4-3 m). Used in mesic forest restoration on Oahu and Molokai, and in breeding programmes as the source of scent in modern hibiscus hybrids. Container culture in pots of 15 gallons (57 L) or more allows growing under glass outside the tropics.

How to Identify

Flowers are white throughout the petals with a long projecting staminal column that is pink to red in most plants, which separates the species from the yellow-flowered H. brackenridgei and the red-flowered H. kokio. Petals are broad and overlapping, and the column extends 1-2 inches (2.5-5 cm) past the petal tips. Leaves are glossy and hairless with red veins on the underside. A light scent from the open flower is detectable at close range, which no other Hawaiian Hibiscus spp. produces.

Appearance

Size & Dimensions

Height6' - 30'

Width/Spread6' - 15'

Reaches mature size in approximately 6 years

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~52 weeks

Spring Summer Fall Winter

Flowering continues through the year with the heaviest output between February and June. Individual flowers open at dawn and close by evening, lasting a single day, and a mature plant opens 3-15 flowers a day at peak. Capsules ripen over 6-8 weeks and split into five valves releasing hairy brown seeds. Plants begin flowering 2-4 years from seed or 12-18 months from cuttings.

Detailed Descriptions

Flower Description

White with a pink to red staminal column

Foliage Description

Glossy dark green with red-tinged veins

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-10 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.0(Neutral)

357912

Soil Types

loam rocky silt

Drainagewell drained

Water & Climate

Water Needs

Medium

Frost Tolerance

tender

Time to Maturity

2-4 years to flowering size

Care & Maintenance

Care Guide

Hibiscus arnottianus grows in full sun to half shade with 4-10 hours of direct light, in free-draining loam or rocky volcanic soil at pH 5.5-7.0. It requires steady moisture rather than seasonal drought, and 40-100 inches (1,000-2,500 mm) of annual rainfall or the irrigation equivalent maintains flowering. Hardiness runs to USDA zones 9b-11, with foliage damage below 30F (-1C) and root death below 25F (-4C). Balanced fertilizer every 8-10 weeks through the warm season sustains continuous flowering, while high-nitrogen feeding produces leafy growth carrying fewer flowers. Chinese rose beetle skeletonizes leaves overnight in warm wet weather, and aphids, whitefly, and hibiscus erineum mite colonize soft shoots. Plants are renewed every 10-20 years, and grafting onto vigorous rootstock is common practice in humid lowland gardens.

Pruning

Plants are pruned in early spring ahead of the main flush, cutting the previous season growth back by one quarter to one third to hold the framework compact. Flowers form on new wood, so pruning after midsummer removes the following flush. Water shoots from the base are thinned to 3-5 stems. Cuts into wood over 2 inches (5 cm) in diameter regenerate slowly and often die back.

Pruning Schedule

early spring