These evergreen shrubs or small trees produce lovely red, purple or yellow flowers. The flowers are actually long spikes of tiny flowers with very long stamens, giving these plants the nickname "bottlebrush". The textured bark gives the appearance of an old tree even on a 3-4 year old plant.
Callistemon from the 2005 Australain Plants as Bonsai Exhibition held at the Australian National Botanic Gardens
Callistemon is a genus of around 30 species in the Myrtle family (Myrtaceae). All except four species are endemic to Australia, the others occurring in New Caledonia. Callistemons are commonly known as "bottle brushes" because of the cylindrical, brush-like shape of the flower spike.
A sunny position will usually produce the best flowering but plants will tolerate anything except total shade.
If you can provide cool conditions in winter and a sunny position in summer, these plants will be easy to grow. Some varieties are susceptible to frost damage.
Callistemon Viminalis or Captain Cook from the 2005 Australain Plants as Bonsai Exhibition held at the Australian National Botanic Gardens
Callistemons naturally grow on moist sites, therefore they enjoy a reasonable amount of moisture as bonsai. Daily watering is essential in summer and a shallow tray may be utilised.
They are quite vigorous growers and require heavy pruning after flowering. They can be cut back to bare wood at this time and will back shoot well. Finger pinch the new tips year round to maintain the shape. Most styles are possible even full cascade.
Fertilize heavily in summer and Osmocote or similar year round in the soil.
Potting must be done prior to a growth period just as the buds are swelling. Add a little extra humus or similar for water retention. Bottlebrush are easily collected (Yamadori) and the best time is early Spring prior to the regrowth.
Callistemons can be propagated by seed (sown in Spring) or cuttings (taken late in Summer or early Autumn). Propagation from cuttings is generally a more reliable method particularly if the leaves are removed from the lower half to two-thirds of each sterile. Make cuttings about 75-100 mm in length and wound the lower stem by removing a sliver of bark and treat with a rooting hormone.
Yamadori (collection) is by far the most preferred method however if you can't collect from the wild or a garden, haunt the older nurseries and look for a good stout trunk with movement, as big as you can find, as big as you want. Reduce the tree from whatever height to 20cm or so and within weeks it will be throwing out shoots everywhere so you can develop branching. Within 2 years it will make a credible bonsai.
PESTS OR DISEASES
The worst known pests are Sawfly larvae which are unfortunately rather common. They are a bronze - green colour with a pointed tail and occur in large groups. They can inflict a great deal of damage to the foliage quickly. They should be physically removed either by hand or with a jet of water from a hose. Scale also can affect Callistemon and can be removed by a strong jet of water or treatment with white oil.
Another pest that can be troublesome is webbing caterpillar. These grubs more commonly attack related genera such as Melaleuca and Leptospermum but can cause damage to certain Callistemons (the cultivar C."Little John" seems particularly prone). Again, a jet of water is effective treatment.
A hardy native with beautiful Spring colour and old looking textured bark. C. Little John is my favourite however best success will be achieved using species native to your local area.