A newly planted weeping bottlebrush trees (Callistemon viminalis) probably looks more like columnar shrub than a weeping tree, but don't despair. It just needs some time and an occasional pruning. If you don't shape it, it will grow into a large shrub. Prune it a little each year and it will gradually grow into a showy tree with long, gracefully weeping branches and bottlebrush flowers.
Use hand pruners for branches smaller than 1 inch in diameter and loppers for branches between 1 and 3 inches in diameter. Always use sharp pruners or loppers. Use bypass pruners rather than anvil pruners. Bypass pruners make a cleaner cut while anvil pruners tend to crush and damage stems. Dull blades will tear the bark, leaving the weeping bottlebrush vulnerable to diseases and insects.
Sterilize the pruners or loppers before using them. Soak them in household disinfectant for five minutes. Rinse the disinfectant off with clear water. It can damage the tree.
When to Prune
Prune the weeping bottlebrush tree in summer after it finishes blooming. Do not prune it in fall. New stems the plant produces after pruning may not harden before winter, resulting in frost and freeze damage.
Changing a Shrub into a Tree
Begin pruning the weeping bottlebrush tree the third year after planting. Young trees need all of their branches to produce energy while they are getting established. Cut off all of the branches on the lower one-fourth of the tree to reveal the trunk. Make the cuts parallel with the tree trunk and about 1/4 inch beyond the branch collar. Additional lower branches can be removed in subsequent years to reveal more trunk and raise the canopy. Never remove more than one-fourth of the tree's branches at one time.
Prune off all of the flowers as they fade. If you miss a few flowers, they will form seed pods. Remove them right away. Make the cut into the branch behind the flower and 1/4 inch above a growth bud or set of leaves. Removing flowers before they form seeds helps the plant produce more flowers next year.
Remove dead and diseased branches at any time of year as soon as you notice them. If only part of the branch is diseased or dead, you don't have to remove the entire branch, only the part affected. Make the pruning cut into the healthy part of the branch 1/4 inch beyond a growth bud or set of leaves.
Disinfect the pruners or loppers between cuts when pruning out diseased branches to help prevent spreading the disease to a healthy branch.
Removing Frost and Freeze Damage
Weeping bottlebrush grows in the warm climates of U.S. Department of Agriculture plant hardiness zones 9 through 11. The tree can suffer frost or freeze damage even when it is growing within these zones if hard frosts or late freezes occur after it begins to put on new spring growth.
Wait until after the weeping bottlebrush tree blooms to remove frost-damaged branches. This will give the tree time to recover and prevent the removal of branches that were not as badly damaged as they first appeared. Make pruning cuts into healthy wood beyond the damaged area 1/4 inch above a growth bud or set of leaves.