Castanospermum australe or Moreton Bay chestnut

Care of the tree Castanospermum australe or Moreton Bay chestnut

The genus Castanospermum, family Fabaceae, includes a single species of tree native to Australia: Castanospermum australe.

Common names: Moreton Bay chestnut, Blackbean. This species is native to Australia and to the Pacific islands.

They are evergreen trees that grow fast in their youth and slow when they are established. These rounded crown trees reach 40 meters (131.2 feet) in height in nature; indoors they can be potted for many years before becoming too large; in the garden they do not usually exceed 20 meters (65.6 feet) in height. They are interesting for their bright pinnate leaves that reach 60 cm (1.96 feet) in length. The flowers are yellow and appear in clusters but do not usually bloom indoors. They bloom in summer. The fruits are long pods up to 20 cm (7.87") in length that house seeds the size of chestnuts that are poisonous by ingestion.

They are used as houseplants but make a fantastic shade tree in gardens with tropical and subtropical climates. It's important not to plant it less than 10 meters from buildings, swimming pools or sewers as it develops aggressive roots.

Castanospermum australe needs an illuminated exposure but without direct sun in the central hours of the day; they prefer a location facing east or west. Outdoors it prefers full sun but can live in semi-shade. The winter temperature should not be less than 10 ºC (50 ºF); the ideal temperature of rest is of 15 ºC (59 ºF).

The soil (potted) can be a mixture of garden substrate, coarse sand, peat, and a little lime. Outdoors they prefer well-drained soil with abundant organic matter and slightly clay. Transplant in spring to a pot one size larger when the roots come out from below the container.

Water with lime-free water regularly so that the soil does not dry out but does not flood. The environmental humidity must be medium-high; spray the leaves in summer periodically with lime-free water.

Fertilize in spring and summer once a month with mineral fertilizer.

They tolerate formation pruning in early spring.

They can be attacked by fungi if there is excess watering and by insects if the humidity is too low.

They propagate by seeds sown in spring at about 18-25 ºC (64-77 ºF). When the plants have a couple of leaves they can be transplanted.