There are many species of small trees and shrubs that are referred to as "bottle brush," several of which are native to the United States. These plants are called bottle brushes because they have flowers that look like the bristly scrub brush used to clean drinking glasses. The only true genus of bottle brush shrubs and trees is callistemon, which is native to Australia. These small trees and shrubs are evergreen with fragrant, bristly flowers that bloom from July to August. Hardy in zones 9 and above, bottle brush shrubs attract hummingbirds, bees and butterflies. Bottle brush shrubs bloom on new growth, so they can be pruned in spring and again after flowering.
Prune in spring after new growth starts by tip pruning or cutting 2 to 3 inches back into the branches. Make the cut just above a strong bud. Tip pruning allows you to shape your bottle brush and encourages branching, creating a bushier shrub with more flowers. If you like the shape of your shrub, skip this step.
Deadhead bottle brush shrubs in late August after flowers have faded. Make cuts just behind the flower spikes. Deadheading removes seed pods, allowing your plant to concentrate on putting out new growth which will increase flowering the following year. Deadheading will also keep your shrub bushy and full.
Cut bottle brush shrubs back to the ground in spring after you see new growth. Older shrubs that have few flowers or are starting to look ragged benefit from this rejuvenation pruning. Use a pruning saw to cut branches as close to the ground as you can. The shrub will re-grow from its roots more vigorous than before.
Apply 2 to 3 inches of compost or a low-phosphorus commercial fertilizer like 10-5-10 after a rejuvenation pruning. The compost or fertilizer will help kick-start new growth.