Mature plants of Aloe castanea may be 3 m tall, characterised by repeated branching near the base of the stem and further up. This plant is literally a small tree in its maturity (SA Tree List No. 28.6).

The rosettes are densely leaved. Leaves may be 1 m long and 10 cm wide. They are glaucous, meaning bluish-green, sometimes pale grey in colour. The leaves are without spots or lines, but they are channelled to the apices. Traditionally the dry leaves at the bottom of the rosettes were removed, burned and the ashes used for keeping weevils from grain (Coates Palgrave, 2002; Reynolds, 1974).