Bottlebrush Bonsai by Ken Goebel

Bottlebrush (Callistemon) is a genus of 34 species of shrubs in the family Myrtaceae, all of which are native to Australia. This subtropical tree is evergreen with a moderate growth habit, and can grow up to a height of 15 feet, although the trees can be pruned to keep them shorter.

Bottlebrush trees produce numerous spikes of flowers in shades of green, pink, purple, red, white and yellow. The flowers attract bees, butterflies and hummingbirds. Seedlings will bloom in 5 years or less. Bloom is most profuse in the spring and flowers sporadically throughout the summer. The unusual flowers of Bottlebrush are made up of a spike of small blooms with very long stamens and looks like a bottle brush. The flowers appear at the tips of the trees’ drooping stems. The stems continue growing once the blooms fade to prepare for next year’s show. Once the showy blossoms go over, they are replaced by woody seed capsules.

The 2-4 inch long evergreen leaves of the bottlebrush tree are dark green, narrow and leathery. Leaves are linear to lanceolate and are not shed in the winter.

The textured bark gives the tree an old appearance even when it is a few years old. Branches will become brittle and strong winds easily damage or snap them.

There are three species most suitable for bonsai:

Callistemon rigidus – A stiff growing bottlebrush with red blooms and sharp tipped leaves. It will grow to 15 feet tall and 10 feet wide. It is moderately salt tolerant.

Callistemon citrinus - The lemon bottlebrush tree. The name refers not to the flower color which is bright red, but to the scent of the crushed leaves. Callistemon citrinus will reach a height of 12 feet and spread to 9 feet. It has smaller leaves and flowers and its bark has the deepest grooves. Callistemon citrinus 'Little John' is a dwarf sport. It is a slow grower to about 3 feet tall and wide. It is one of the best bottlebrushes to plant as a bonsai. It also differs from the other Callistemon varieties due to its blue-green foliage.

Callistemon viminalis - This is the weeping bottlebrush tree. It grows to a height of 20 feet with an equal spread. Its pendant growth habit makes it attractive even when it isn’t blooming. This variety is commonly seen in Central Florida. Its leaves and flowers are larger than the citrinus. The trunk is much smoother than the citrinus and slower to develop than the rigidus.

Basic Care of Bottlebrush (Callistemon species)

Light: Place your Bottlebrush in full sun to partial shade. Full sun produces more flowers. The plants will tolerate anything except total shade.

Temperature: Bottlebrush grows in a warm climate, and is hardy in zones 9-11. The trees do not tolerate extended periods of cold weather. Protect from any sustained freeze and/or heavy frost. When outdoor temperatures reach 45-50 deg. F or less, the Bottlebrush should be brought indoors. Placement near a south-facing window is best. Other window positions will require supplemental lighting.

Watering: The bottlebrush tree requires moist, well-draining soil during the summer months, and much drier in winter. Cut back on watering during the winter months but do not allow the soil to remain dry for extended periods. Short periods of drought are tolerated. Never let the soil dry out completely.

Feeding: Use a well-balanced, liquid fertilizer at half strength throughout the growing season with a little extra phosphorus in early spring for flowering. Include a sustained-release granular feed year round in the soil.

Pruning and Wiring: Bottlebrush trees are vigorous growers and require heavy pruning after flowering. Cut back at this time and shoots will grow back in a few weeks. It can be severely top pruned to keep the tree at the desired height and shape, but leave some growth on each branch. Finger pinch the new tips year round to maintain the shape. Keep terminal buds cut back to increase ramification. Cut off any damaged, dead or diseased branches. Remove dead flower spikes and fruit clusters.

Older branches that have become woody are very hard to bend and should not be wired. Bottlebrushes are quick growers and younger branches should be wired loosely, allowing wire to stay until the branch becomes woody.

Styles and Forms: Most styles are possible, even full cascade and landscape. They are often multi-trunked. The vimanilis with its weeping habit is best suited for the weeping style.

Propagation: Propagation is either by cuttings taken late in Summer or early Autumn, or from the rounded seeds (sow in Spring near the top of the soil). Propagation from cuttings is generally a more reliable method, particularly if the leaves are removed from the lower half to two-thirds of the

stems. Make cuttings about 3-4 inches long, and wound the lower part of the stem by removing a sliver of bark and treating with a rooting hormone.

Repotting: Spring is best, but repotting can be done into the summer. Roots can be severely cut back in Spring as long as the main root ball is not disturbed. Carefully comb out roots and remove only the largest roots. Larger trees may best be root pruned over two seasons. Once potted the tree will respond quickly to root pruning with a flush of new growth.

Soil: Bottlebrush prefers acidic soil mixtures. An easy solution is the addition of some dried sphagnum moss to the soil blend. Use a well-drained, rich soil. Amend clay soil with rich organic matter and coarse sand. Amend sandy soil with organic matter. Soil pH rating 5-6.

Pests and Diseases: Spider mites and aphids can be a problem with the new flush of spring growth. The worst known pests are Sawfly larvae which are unfortunately rather common. They are a bronze - green color 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 the Bottlebrush, and can be removed by a strong jet of water or treatment with white oil.