Smoke tree (Cotinus coggygria) grows as a small tree or shrub. The plant's flower clusters, which are gray or violet in color and wispy, resemble the spiny flower clusters of the bottlebrush tree and give the tree its common name. Topping out at 20 feet in height, smoke tree requires frequent pruning to maintain a tree's structure. Gardeners should prune annually in late winter to early spring, once frost danger passes. The tree grows in hardiness zones 5b to 8.
Check your smoke tree for dead, damaged or diseased limbs, which need to be removed for the health of the tree. Damaged or diseased limbs will look markedly different from healthy limbs. They may bear cankers or growth or appear stunted, discolored or broken. Dead limbs will not move with the wind and will feel hollow.
Clip off dead, diseased and unhealthy wood using anvil pruners for thin cuts and lopping shears for those thicker than 1 inch. Cut all wood back to a healthy lateral branch or cut it off at the base. In between each cut, sanitize your pruning tools by spraying them with disinfectant. This prevents you from accidentally spreading disease to healthy limbs.
Prune off suckers that grow along the trunk or out of old pruning sites. These vegetative shoots will not bear flowers. They sap energy from the smoke tree and can weaken it.
Train the tree by selecting a central leader and removing competing growth, such as offshoots from the central leader or growths of other branches that rival the central leader. Leave one to two offshoots from the central leader and clip off all others. A smoke tree requires frequent trimming to maintain its structure since it tends to be shrubby. Prune off any limbs that detract from the tree's appearance, cutting them off at the base.
Thin out the canopy by removing low-growing or downward-growing branches and branches that compress other limbs. This improves air circulation and keeps the tree healthy.
Clip the tips of branches if they grow too long. Cut then back to a lateral branch. Work one branch at a time and use anvil pruners; do not use hedge clippers.