Callistemon is a word derived from the Greek: ‘kallis’ (beauty) and ‘stemon’, the showy part of the flowers.
Callistemon, commonly called bottlebrush from the shape of the flowers, is an Australian genus of about 25 species. While some are shrubby and others tree-like, they grow in every state bearing a range of colours from red, purplish, pink, green cream and white. The flowers are followed by capsular woody fruit, some persisting for many years.
While all of the species can be grown from seed in spring (select capsules from old wood), cultivars of specific colour are best grown from firm new cuttings taken in late summer and autumn. As callistemon hybridise readily, it can never be guaranteed that the seedlings will be the same as their parent plant.
Most are hardy to light frosts but young plants might need some frost protection for the first year after spring planting.
The plants have proved to be very hardy as they mature and will grow in most well-drained but moist soils – their natural habitat is often alongside the edges of streams or swamps. They respond well to pruning behind the spent flowers annually, a habit which will encourage dense growth and more flowers.
Due to their proven beauty and ease of culture, callistemons are not only used in home gardens but streetscapes, parks and commercial sites. Two species in particular – C. citrinus and C. viminalis – have produced many bird attracting cultivars for gardens.
C. citrinus, the crimson or lemon-scented bottlebrush, is found on central plains and lower mountain slopes from Victoria to central Queensland. A shrub to 3 metres, it is usually on a short trunk with many low branches forming a compact bush.
Some of the most outstanding garden cultivars include: ‘Austraflora Firebrand’, a semi-prostrate crimson brush form 75cm x 2-3m with special value as a ground cover of banks and steep slopes; ‘Mauve Mist’ has prolific crops of lilac- purple brushes ageing to rosy magenta with deeper anthers; ‘Reeves Pink’ is a Victorian cultivar with phlox-pink brushes borne singly or in clusters; ‘Splendens’ 4m x4m with a dense habit and ‘Endeavour’ 2 x 2m are both great hedge plants with brilliant crimson flower spikes for most of the year.
Many of the shrubby forms of C. viminalis have become invaluable garden specimens. ‘Captain Cook’ has a small tree like growth to 2.5m, and red brushes in spring with an additional flush in autumn. ‘Little John’ is a dense rounded shrub to 1.5m, and flowering deep crimson in spring, spasmodically other times.
Applications of slow release fertiliser for native plants in spring and autumn will promote good growth and can result in two flowering periods each year – one near the end and the other about four or five months later.
Because of their beauty and hardiness bottlebrushes, have a wide application in the landscape as well as horticulture. Not only are they decorative street trees but groups of the same or mixed colours offer an outstanding effect in home gardens.
All respond to pruning to make more compact growth, and if scale insects become troublesome, the use of white oil after the bees have gone to bed will be beneficial.