The Callistemon (Bottlebrush) - a great Australian native
The callistemon belongs to the Myrtaceae or myrtle family and is endemic to Australia. This evergreen shrub has found its way into the hearts of gardeners in several other countries. It gets its common name of 'bottlebrush' because of the multi-stamened, cylindrical brush-like flowers which look for all the world like a bottlebrush.
The plant is ideal as a spectacular screening plant or an ornamental bush. The nectar is attractive to native birds. In the wild, it is found in moist soils in open or woodland sites. It likes warmth, moisture and sunlight.
The callistemon is closely related to the melaleucas which have similarly shaped flower spikes. Currently there are about 34 species of Callistemon. Most occur in the east and south-east of Australia. Two species are found in the south-west of Western Australia and four in New Caledonia. These areas cover a range of climatic conditions from the northern tropics to the more temperate southern regions.
Although they are often found in creek beds or in areas prone to flooding, most will tolerate drought and limited maintenance. Most soils are suitable bar highly alkaline types. A position in full sun will produce the spectacular flowers for which the bottlebrush is loved. If kept fairly dry, it will withstand light frosts or short cold spells in winter.
Flower heads are mostly red but yellow, green, orange and white are seen too. These woody shrubs are rather slow to grow. Large species may eventually reach 15 metres while others remain close to the ground at 0.5 metres so there is a suitable bottlebrush for every situation. The leaves are linear to lanceolate in shape.
The potential of the bottlebrush as a garden specimen was quick to be recognised. It was quickly incorporated into domestic gardens in the early days of Australian European settlement. Joseph Banks introduced the crimson bottlebrush to Kew Gardens in Britain in 1789. Callistemons are also grown in India and are well known in America where they are most suited to zones 9 to 11.
Callistemons will appreciate a monthly feed with a liquid low-phosphorous fertiliser. Many Australian natives react badly to too much phosphorous. In the spring, top-dress by applying fertiliser and mulch around the plant, keeping it back from the trunk. This will help retain the moisture in the soil and reduce the establishment of weeds.
The flower spikes consist of a number of individual flowers and form in spring and summer. The pollen of the flower sits on the tip of a long coloured stalk or filament. These filaments give the flower its colour and distinctive shape.
The flowers produce small woody fruits which form in clusters along the stem. These may be held on the plant for a number of years before opening to disperse hundreds of tiny seeds. Some fruits open after about twelve months; others are stimulated to open by bushfires.
Light pruning can be undertaken to keep the plant in shape. Don't cut back into the middle of the plant where there is little or no foliage. Tip pruning can be done as new growth appears but some flowers may be sacrificed as the next year's flowers will be formed on the end of this growth.
Pruning just behind the flowers as they finish is probably the best method of pruning the callistemon. Older callistemons which seem to be 'tired' can be rejuvenated by cutting back to ground level. This is basically what happens during a bushfire. Such heavy pruning usually invokes a vigorous response. Extra feeding at this time will help.
Propagation from seed is simple. Store the unopened fruits in a warm place in a paper bag until the fine seeds are expelled. Sow in a freely draining mix specially formulated for seed-raising. Because bottlebrush hybridise so easily, use cuttings if you wish to duplicate the parent plant. Take cuttings from semi-mature wood.
The nectar of callistemons is irresistible to insects and birds. The larvae of hepialid moths may use the callistemon as a food plant, burrowing horizontally into the trunk then in a vertical direction towards the ground.
There are now many cultivars and hybrids. Many of the hybrids have either Callistemon viminalis or Callistemon citrinus as a parent.
Callistemon 'Little John' is a dwarf cultivar with attractive blue-green foliage and masses of flowers.
Callistemon viminalis or weeping bottlebrush is widely cultivated. The bright red flower spikes are highly attractive to birds. This variety can be frost tender and grows 5 to 7 metres tall.
Callistemon subulatus only reaches 1 to 3 metres tall and tolerates quite wet conditions. It is a free flowering species with red flower spikes in summer.
The willow bottlebrush, Callistemon salignus, has white papery bark and is quite hardy, although somewhat frost tender in cold climates. The narrow foliage is attractive and the flowers are generally white or with a green tinge although there are pink, red and mauve forms as well. It is a great garden and street tree and reaches 5 to 12 metres.
The alpine bottlebrush or callistemon pityoides is very hardy. It is variable in form with some growing to a compact bush of around a metre high while others form erect shrubs to 2 metres. Yellow blooms are produced in spring and summer. It is frost hardy and tolerates heavy pruning.
Another tough, frost hardy species is the lemon bottlebrush or callistemon pallidus. It tolerates most soil conditions but is best in full sun. The flowers are lemon-coloured and appear in summer. Plants grow to around 3 metres.
The Kingaroy bottlebrush is used as a street tree in Kingaroy, Queensland. It is a good choice for tropical areas as long as there is no risk of frost. It has a weeping habit with lemon-coloured flower spikes.
The crimson bottlebrush, Callistemon citrinus, is often used as one parent of cultivars. It is hardy and responds well to hard pruning. It grows well in wet conditions and should be lightly pruned and fed after flowering.
Callistemon brachyandrus or prickly bottlebrush has prickly leaves and does best in well-drained soils in full sun. It is a great choice for hot, dry areas. The red flower spikes are small but the tips become covered in yellow pollen and are very attractive. It forms a rounded shrub of some 3 metres.
These are only some of the varieties available. Your garden centre representative will be able to suggest more varieties suited to your particular area.