Smoke bush is a large ornamental shrub or small tree prized for its rich burgundy-red to eggplant-purple foliage in the fall and the subtle ruby and gray flowers in the spring and summer. Known botanically as the genus Cotinus and also commonly as smoketree, smoke bush is considered slow growing and requires little pruning. It is naturally a multitrunked, spreading plant, but the seedlings and young trees can be pruned to resemble a more compact and classic upright tree form.
Prune your seedling smoke bush in the spring after the last threat of frost has passed and through the midsummer. Later pruning may encourage new growth that would be killed by winter temperatures.
Pinch back the tips of any errant young branches that shoot out beyond the general line and natural shape of the canopy. Take the tender branch tip between your thumb and forefinger and use your fingernail to cut and snap the terminal tip off 1/4 inch above a leaf axil. This will preserve the form of the canopy and encourage new side branching and fullness.
Prune away one or more excess trunks that you may not want to grow. Smoke bush will not perform well if all but one or two of the trunks are pruned, but reducing the number of trunks to three or five will not harm the plant. Cut the unwanted trunks down to the crown of the plant at the soil line and remove repeat water sprouts or new shoots as needed.