The bottle brush (Callistemon citrinus) is an evergreen shrub that is native to Australia. The shrub is hardy to plant in USDA growing zones 10 to 11, where there is little risk of freezing temperatures. Hummingbirds are attracted to the bright, brush-shaped flowers that hang from the plant. It grows well as both a landscape and container plant.
The bottle brush is an evergreen shrub that has a height and width that ranges in size from 5 to 20 feet. It has dark green foliage and produces fragrant, hanging red flowers. The flowers have the appearance of a cylindrical brush used to clean bottles, and go into bloom from midspring to midsummer.
Bottle brush prefers a well-draining sandy loam or clay loam soil with an acidic pH. Soggy soil promotes root damage. The location should also provide full sunlight, because shade will limit flower production. The soil should be tested to verify it has a pH of 5.5 to 6.5. Ground rock sulfur can be worked into the soil to lower the pH number and make it more acidic.
The bottle brush shrub is considered drought tolerant once it becomes established, but the shrub will perform better when given supplemental water during the hot summer months. Provide the plant with a deep watering to a soil depth of 10 inches when the weekly rainfall amount is less than an inch. Mulch placed over the rootball area of the shrub will assist with soil moisture retention. A balanced fertilizer that is water soluble should be applied each month in the spring and summer season to promote green foliage and flower production. The shrub can be pruned each year in early spring to keep the plant in shrub form.
Bottle brush can be propagated to produce additional plants by taking semi-hardwood cuttings in late summer. Semi-hardwood cuttings are taken from current-year branch growth that is woody and beginning to mature. The cuttings will form roots if you dip the cut end into rooting hormone and stick it into a tray filled with moist rooting medium. The tray should be covered with plastic to create a greenhouse environment and set in a warm location with indirect light until roots are formed.
The bottle brush tree is susceptible to fungus infections when the soil is oversaturated around the root and stem. Gall is an infection that forms wartlike growths on the branches and stems. Shrubs with large galls should be removed and destroyed, because there is no treatment for the disease. Chlorosis is a systemic disease that causes the new leaf growth to turn yellow due to an iron deficiency. The soil can be treated with iron chelate or iron sulfate.