Bottlebrush, or Callistemon, is a genus of about 30 evergreen flowering trees or shrubs native to Australia and New Caledonia. Popular in gardens around the world, they also work well in car park islands, as hedges or as lawn trees, according to Edward F. Gilman and Dennis G. Watson from the University of Florida IFAS Extension.
Bottlebrush plants vary in size depending upon the species. They have dark grey bark and narrow greyish-brown twigs that bear heavy foliage near the ends of the branches. The dark green, opposite or alternating lance-shaped leaves range from 1 to 3 inches in length. Bottlebrush shrubs and trees produce showy clusters of 2- to 4-inch flowers. The blossoms have tiny, inconspicuous petals with long stamens that grow in clusters around the flower stem, giving the flower a "bottle brush" appearance. Most bottlebrush flowers are red, but some cultivars produce pink, orange, white or yellow flowers. Small woody seed capsules replace the blossoms.
Callistemon citrunus, or red bottlebrush shrubs, grow between 10 and 15 feet tall with a 10- to 15-foot spread. They have thorny, drooping branches, multiple trunks and bright red flowers. Callistemon violaceus, a bottlebrush cultivar, produces purple filaments with yellow tips, while Callistemon pallidus or creamy callistemon yields cream-coloured flowers. The weeping bottlebrush Callistemon viminalis grows between 15 and 20 feet tall with an equal spread; it has an open, drooping crown, light green lance-shaped leaves and vivid red flower spikes.
Most bottlebrush trees and shrubs thrive in United States Department of Agriculture hardiness zones 10 and 11, which includes cities such as Miami, Florida, Honolulu, Hawaii and Victorville, California. They are not usually cold-hardy at temperatures lower than -6.67 degrees C. They prefer full sunlight but can tolerate partial sun. The plants grow best in moist, well-drained soil. Bottlebrushes are generally drought-hardy, but they cannot tolerate full shade. A yearly pruning removes seed capsules and spent flowers and encourages new growth.
Pests, Diseases and Problems
Armoured scales, which are immobile insects covered by a rounded- or oval shell-like body cover, occasionally feed on bottlebrush plants by piercing the stems or foliage and sucking out sap. The Sphaeropsis tumefacens fungus causes twig galls that can detract from a bottlebrush tree's beauty. Plant-parasitic nematodes in the soil can cause mineral deficiencies; the leaves turn yellow or brown and the plant's growth may be stunted. Too much or too little water causes foliage wilting and drop; leaves may also turn brown and fall from sunburn, frost damage, excess salt in the soil, or wind damage.