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Castanospermum australe

Blackbean

Fabaceae Eastern Australia

Attracts Pollinators Container Friendly

SunFull Sun – Part Shade

WaterMedium

HardinessZones 10–11

Overview

Castanospermum australe is a large evergreen tree reaching 25-60 feet (8-18 m) tall and 20-40 feet (6-12 m) wide in cultivation, taller in rainforest, with a dense rounded crown. Leaves are pinnate, 6-18 inches (15-45 cm) long, with 9-15 glossy dark green leaflets. Pea-shaped flowers, 1-1.5 inches (2.5-4 cm) long, open yellow and age through orange to red, borne in short clusters directly on the trunk and older branches in spring and early summer. Large woody pods 4-10 inches (10-25 cm) long follow, each holding three to five rounded seeds 1-1.5 inches (2.5-4 cm) across. The raw seeds contain saponins and the alkaloid castanospermine and are toxic if eaten without lengthy traditional processing. Growth is slow to moderate; trees reach flowering size in 8-12 years. The large pods and seeds drop and can litter paved areas beneath the canopy.

Native Range

Native to coastal eastern Australia from north Queensland to northern New South Wales, with related populations in the Pacific. Grows in subtropical and tropical rainforest, especially along rivers and on alluvial flats in deep, moist soils.

Suggested Uses

Planted as a shade and street tree in parks and large gardens in frost-free climates, spaced 25-40 feet (8-12 m) apart. Used as an indoor foliage plant when young, grown from the large seeds. The size, dropping pods, and toxic seeds limit its use in small or child-used gardens.

How to Identify

Identified by pinnate leaves with 9-15 glossy leaflets and by pea-shaped flowers that open yellow and age orange to red, borne directly on the trunk and main branches. Woody pods 4-10 inches (10-25 cm) long contain large chestnut-like seeds. The cauliflorous flowering and large seeds separate it from other rainforest legumes.

Appearance

Size & Dimensions

Height25' - 60'

Width/Spread20' - 40'

Reaches mature size in approximately 12 years

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~6 weeks

Spring Summer

Flowers in spring and early summer (September to January in its native range). Flowers emerge directly on the trunk and older branches over about four to six weeks. Mature trees flower more heavily, while young trees may not flower for several years.

Detailed Descriptions

Flower Description

yellow aging orange to red

Foliage Description

glossy dark green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 5-8 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 clay

Drainagewell drained

Water & Climate

Water Needs

Medium

Frost Tolerance

tender

Time to Maturity

8-12 years

Care & Maintenance

Care Guide

Grows in full sun to part shade in deep, moist, well-drained soils. Water regularly when young and during dry periods, reflecting its riverside rainforest origins. Tolerates light frost once established, though young growth is damaged by hard frost. Grows slowly and develops a large root system, so it needs space well clear of paving and pipes. Few serious pests occur. The seeds contain castanospermine and saponins and are toxic if eaten raw.

Pruning

Prune in late winter to early spring to remove dead or crossing branches and to shape young trees. Mature trees need little pruning beyond deadwood removal. Heavy cuts into large limbs heal slowly in the dense wood.

Pruning Schedule

winterearly spring