Eucalyptus robusta
swamp mahogany
Coastal eastern Australia (Queensland and New South Wales)
Overview
Eucalyptus robusta is a large evergreen tree reaching 65-100 feet (20-30 m) tall with a spreading crown 30-50 feet (9-15 m) wide and a single straight trunk. The bark is thick, soft, and reddish-brown, with a fibrous, deeply furrowed stringybark texture that persists to the smaller branches. Adult leaves are broad and lance-shaped, 4-6.5 inches (10-17 cm) long, dark glossy green above and paler below, with prominent veins. Clusters of 7 to 13 cream-white flowers open from club-shaped buds mainly in autumn and winter, drawing nectar-feeding birds, bats, and insects. Woody capsules are cylindrical to barrel-shaped, about 0.4-0.7 inch (10-18 mm) long, with the valves enclosed near the rim. The species grows naturally in coastal swamps and behind estuaries, tolerating waterlogged and brackish soils that few large trees withstand. Its size, spreading surface roots, and heavy litter of bark and capsules make it suited only to large open sites. It is naturalized and treated as a weed in parts of Florida and Hawaii. Foliage is browsed by koalas within the native range.
Native Range
Eucalyptus robusta is native to the coastal lowlands of eastern Australia, from southeastern Queensland south along New South Wales. It grows in swamp margins, behind coastal dunes, and on the edges of estuaries on heavy or sandy soils that are seasonally waterlogged.Suggested Uses
Used as a shade and shelter tree in large coastal gardens, parks, and on damp or saline sites where other trees fail. Planted in windbreaks and for soil stabilization on swamp margins. Spaced 30-50 feet (9-15 m) apart as a canopy tree.How to Identify
Appearance
Size & Dimensions
Height65' - 100'
Width/Spread30' - 50'
Reaches mature size in approximately 15 years
Bloom Information
Cream-white flowers open mainly in autumn and winter, roughly April to September in the native range, though scattered flowering can occur in other months. The clustered flowers carry abundant nectar and are visited by birds, flying foxes, and insects. Buds may take several months to develop before opening.
Detailed Descriptions
Foliage Description
Dark glossy greenGrowing Conditions
Sun Requirements
Requires 6-12 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
Eucalyptus robusta grows in full sun in a wide range of soils, from heavy waterlogged clay to sand, and tolerates seasonal flooding and brackish conditions. Established trees handle short droughts but grow fastest with steady soil moisture. Cold hardiness is limited to about USDA zones 10-11, with young trees damaged by hard frost. Growth is rapid, often 3-5 feet (0.9-1.5 m) per year when young, so wide spacing is needed away from buildings and paving. Surface roots and falling bark and capsules call for an open site rather than a lawn or patio setting.Pruning
Formative pruning while young can establish a single straight leader and lift the crown for clearance. Mature trees need little pruning beyond removal of dead or damaged limbs. Heavy topping produces weak regrowth and is avoided on established trees.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
winter