Gossypium tomentosum
Hawaiian cotton
Overview
Gossypium tomentosum is an evergreen shrub in the Malvaceae reaching 2-5 feet (0.6-1.5 m) tall and 3-6 feet (0.9-1.8 m) wide, with stems arching outward from a short main trunk. Leaves are 1.5-3 inches (4-8 cm) wide with three to five shallow lobes and a dense coat of short hairs that gives the foliage a gray-green cast. Flowers are yellow, five-petalled, and 1.5-2 inches (4-5 cm) across; they open shortly after sunrise and close by mid-afternoon, lasting a single day. Petals carry no dark basal spot. Fruit is a capsule 0.5-0.8 inch (12-20 mm) long that splits into three valves, releasing seeds wrapped in rusty-brown to tan lint 0.2-0.4 inch (5-10 mm) long, too short to spin into thread. Seeds contain gossypol. Growth runs 12-24 inches (30-60 cm) per year and plants flower in their first or second season. Lifespan in cultivation is 5-10 years, after which stems turn woody and flowering thins. Plants collapse in wet or shaded positions and defoliate under sustained overhead irrigation.
Native Range
Endemic to the Hawaiian Islands, recorded from Kauai, Niihau, Oahu, Molokai, Lanai, Maui, and Kahoolawe. It grows in dry coastal shrubland and lowland dry scrub from sea level to about 400 feet (120 m), usually within a mile (1.6 km) of the shore. Substrates include coral sand, aa lava, and dry clay pans on leeward slopes.Suggested Uses
Planted in coastal and dry native Hawaiian gardens at 4-6 foot (1.2-1.8 m) spacing, and used in dryland restoration on leeward shorelines. Leaves and flowers were processed for green and yellow dyes applied to kapa cloth. The species is held in cotton breeding collections as a source of pest-resistance traits, including the absence of leaf nectaries that lowers populations of some insect pests.How to Identify
Appearance
Size & Dimensions
Height2' - 5'
Width/Spread3' - 6'
Reaches mature size in approximately 3 years
Bloom Information
Flowering runs from April through October, heaviest between June and September. Each flower opens near sunrise and closes by mid-afternoon the same day, so a plant shows a fresh set of flowers daily through peak bloom. Capsules mature 6-9 weeks after flowering and split open across a further 2-3 weeks. Flowering stops during overcast, humid spells lasting more than 10 days.
Detailed Descriptions
Foliage Description
gray-green, densely hairy on both surfacesGrowing Conditions
Sun Requirements
Requires 8-12 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
Care & Maintenance
Care Guide
Seed germinates in 7-21 days once the hard coat is scarified or soaked for 24 hours. Water weekly through the first 6 months, then withhold irrigation; established plants grow on 10-20 inches (250-500 mm) of annual rainfall and rot at the crown under regular watering. Soil must drain freely and carries the species at pH 6.5 to 8.0, including coral sand and calcareous fill. Eight or more hours of direct sun are needed for flowering, and plants in part shade produce elongated stems with few capsules. Aphids, whiteflies, and spider mites colonize new growth in still dry air, and cotton stainer bugs feed on developing capsules. Plants are cut back hard or replaced after 5-10 years as flowering declines.Pruning
Stems are cut back by one third to one half in winter or early spring, producing a flush of new shoots that carry the following season flowers. Plants cut to 12 inches (30 cm) from the ground regrow to full size within 12-18 months. Old capsules are taken off in the same operation, which reduces self-sown seedlings around the base. Unpruned plants open out and turn woody at the base within 4-5 years.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
winterearly spring
Container Growing
✓ Suitable for container growing
Minimum container size: 5 gallons