The Nandina, known commonly as heavenly bamboo (Nandina domestica), is a highly valued evergreen shrub in many landscapes. It is admired for its delicate, lacy foliage that transitions through colors, displaying bronze new growth and bright red tones in fall and winter. This shrub produces clusters of small white flowers that develop into showy, persistent red berries, which contribute to its winter interest. Pruning is necessary to prevent the plant from becoming leggy and overgrown, maintaining its naturally graceful, upright form and overall health. The timing of this maintenance significantly impacts the plant’s appearance and vigor.
The Impact of Summer Pruning
Although you technically can prune Nandina at any time of year, heavy pruning during the active summer growing season is generally discouraged. The plant is under increased stress from high ambient temperatures and actively expending energy for growth. Major cuts force the plant to divert significant resources toward healing wounds and initiating new growth. This added stress can weaken the plant’s overall health and vigor.
A major negative consequence of summer pruning is the reduction or complete loss of the plant’s ornamental berries. Nandina produces small white flowers in the spring and early summer, and these blooms must remain on the plant to mature into the bright red berries seen in autumn and winter. Removing significant cane material in the summer will cut off the developing fruit clusters, eliminating the primary source of winter color and appeal. Minor, cosmetic adjustments, such as snipping a single stray or damaged branch, are acceptable. However, any substantial reduction or shaping should be postponed until a less strenuous season.
Pruning Techniques for Nandina
When pruning Nandina, the technique is far more important than with many other shrubs to preserve the plant’s natural, layered aesthetic. This shrub should never be sheared across the top with hedge trimmers, as this ruins its elegant, upright habit and causes it to become dense and unnatural-looking. Shearing also encourages new growth only at the cut points, resulting in a bushy top with an increasingly bare, leggy base.
The correct method is called “renewal pruning” or “thinning,” which focuses on removing individual canes down to the base of the plant. This technique encourages new, vigorous shoots to sprout from the ground, keeping the shrub full and bushy from the bottom up.
To execute this properly, use a staggered approach known as the “rule of thirds,” removing approximately one-third of the oldest, tallest canes each year. Cut these selected canes all the way back to ground level, using sharp bypass pruners or loppers to make a clean cut.
For a more tiered, natural look, you can modify the rule of thirds by cutting some canes to the ground and others to different heights. For instance, remove one-third of the oldest canes completely, cut another third to about half the plant’s height, and leave the final third untouched. Making the height-reducing cuts just above a leaf node ensures the remaining cane will sprout new foliage from that point. This selective removal of older material allows light and air into the center of the plant while promoting the continuous cycle of new, colorful growth.
Optimal Timing for Major Cane Removal
The ideal time to perform major cane removal or renewal pruning on Nandina is during the late winter or very early spring. Specifically, aim for the period when the plant is fully dormant, just before it begins to push out new growth. This timing is beneficial because the plant is not actively photosynthesizing or under heat stress, minimizing the shock of a significant cut.
Pruning during the dormant season allows the plant to immediately put its energy into producing strong new canes from the base as soon as the weather warms. By cutting canes before the emergence of new leaves and flowers, you ensure that the current year’s blooms, which will become the attractive berries, are not inadvertently removed. This schedule allows the gardener to enjoy the full display of winter berries and ensures the subsequent growth flush is robust and healthy. While a light cleanup can be done in late fall after the foliage has colored, late winter provides the best window to prepare the shrub for the coming growing season.