The Royal Purple Smoke Tree (Cotinus coggygria ‘Royal Purple’) is a deciduous shrub or small tree celebrated for its dense, deep-purple foliage, which provides a striking contrast in the landscape. This cultivar is highly valued for the rich, vibrant color of its leaves. Because the plant naturally tends toward a sprawling, multi-stemmed habit, regular and intentional pruning is necessary to direct its growth and maximize its ornamental characteristics. The specific pruning technique chosen will determine the plant’s final form, size, and leaf color intensity.
Optimal Timing for Pruning
Pruning the Royal Purple Smoke Tree is best performed during the late winter or very early spring when the plant remains completely dormant. In most temperate climates, this window typically spans from January through March, before the appearance of new leaf buds. Performing major cuts during this period minimizes stress on the woody plant because it has not yet expended energy on spring growth.
Pruning while dormant allows the plant to direct its stored energy reserves toward vigorous new growth immediately as temperatures warm. Waiting until the plant has fully woken up can result in sap bleeding from the wounds, which, while generally not harmful, can be messy and indicate energy loss. Pruning later in the season should be avoided, with the exception of removing dead or damaged branches, as summer cuts can stress the plant and expose fresh wounds to pests and disease.
Pruning for Maximum Foliage Color
The deepest, most intense purple coloration on the Royal Purple Smoke Tree occurs on its youngest, newest foliage. To exploit this characteristic, gardeners often employ a technique known as “hard pruning” or coppicing, which sacrifices the plant’s characteristic “smoke” flowers in favor of superior leaf color. This method involves cutting the plant back severely before the start of the growing season to stimulate the production of long, juvenile shoots.
To hard prune, you should cut all stems back to a small framework, typically leaving only 6 to 12 inches of the previous year’s growth above the ground or the main trunk structure. Making these heavy cuts requires sharp, long-handled loppers or a pruning saw to ensure clean, smooth wounds that heal quickly. The robust root system, which remains intact, will then push out several long, cane-like shoots that bear leaves with maximum pigmentation throughout the summer. While this technique prevents the formation of the wispy flower clusters, the resulting abundance of deep purple leaves creates a dramatic, shrub-like focal point in the garden.
Pruning to Maintain Tree Shape
An alternative approach is to prune the Royal Purple Smoke Tree to maintain a single-trunk, standard tree form, which allows the plant to produce its decorative, hazy flower plumes. This method focuses on structural integrity and light canopy maintenance rather than stimulating new, juvenile growth. When training a young plant into this shape, select the strongest, most upright stem to serve as the central leader, removing all competing vertical shoots at the base.
Once the desired height is achieved, pruning shifts to thinning cuts, which are made by removing entire branches back to the main trunk or a larger side branch. This practice opens up the canopy, allowing light and air to penetrate the interior, which discourages disease and promotes healthy, well-spaced branches. Removing any branches that cross or rub against one another prevents wounds that could later become entry points for pathogens. This lighter pruning approach preserves the mature wood necessary for the formation of the flower panicles, the feature that gives the tree its common name.
Post-Pruning Care and Potential Issues
After major pruning, thoroughly clean up all cut branches and debris from around the base of the plant to minimize the risk of fungal or bacterial diseases. Pruning tools should be sanitized with a solution of bleach or rubbing alcohol between plants to prevent the transfer of pathogens. Applying a fresh layer of organic mulch, such as wood chips or shredded bark, over the root zone helps conserve soil moisture and moderate temperature fluctuations.
A common issue following hard pruning is the development of suckers, which are new shoots that emerge directly from the base or roots. These suckers should be removed promptly by tearing them off rather than cutting them, which helps eliminate the latent buds at the base. While the Royal Purple Smoke Tree is generally drought-tolerant, providing initial deep watering after heavy pruning can help support the immediate burst of new growth.