How to Prune a PJM Rhododendron
P.J.M. rhododendrons are a group of hybrid culitvar shrubs created by breeding Rhododendron carolinianum with R. dauricum var. sempervirens. According to the University of Connecticut, there are at least seven known culitvars of varying size, spread flower and leaf coloration, but all are considered to be hardy and easy to grow evergreens in the garden. They have a tidy mounding growth habit, blooming in early spring and summer each year and require only light pruning once each year or every few years.
Prune your rhododendron in the summer immediately after the bloom cycle has ended. Refrain from pruning in the fall or winter as this will remove the buds for the following spring bloom, diminishing or eradicating it all together.
Dead head spent flowers on your rhododendron as they die back to encourage fresh bloom and keep the shrub looking fresh and tidy. Pluck the flower heads off with your fingers or trim them off with pruning shears to just 1/4 inch above a leaf node or pair of leaves.
Thin dead, diseased, defoliated or non-flowering branches by cutting the branch on the bias just outside where the problem branch connects to the healthy parent branch or limb.
Reduce the size or spread of the shrub only if necessary by thinning out the longest and oldest branches down to where the meet the parent branch or main trunk. Refrain from shearing off just the tips of the branches, as this destroys the natural form of the plant and inhibits flowering.
Prune Lower Branches Of A Rhododendron
Crawl beneath the rhododendron and look for lower branches you want to remove to achieve the shape you desire. Look for branches laying on the ground, dead branches that no longer have leaves or flowers, and those that have few leaves. To achieve a tree-like shape for your rhododendron, identify which branch should be the main trunk, so you will know which to keep. Cut away the branches with sharp, sanitized pruning shears. Make each cut as close as possible to the adjoining branch, and make the cuts in a direction parallel to the adjoining branch. This prevents the spread of disease in the rhododendron because leaving stubs behind can encourage disease. Sanitize your pruning shears with each new cut you make by dipping them in a solution of household cleaner and water. Wipe them off before cutting the next branch. Commercial household cleaners, such as Lysol or Pine-Sol, are simple to use and the least damaging to tools.
Never remove more than one-third of the rhododendron's living tissue mass in any pruning as this can cause stress on the shrub and induce shock.
- Purdue University: Pruning Ornamental Trees and Shrubs
- University of Connecticut: Rhododendron 'PJM'
- Washington State University: Sterilized Pruning Tools: Nuisance or Necessity?
- North Carolina State University: Pruning Shrubs
- Virginia Cooperative Extension: A Guide To Successful Pruning, Pruning Shrubs
- Virginia Tech: How and When to Prune Rhododendrons
- New York Rhododendron Society: The Art of Pruning
- Henning's Rhododendron & Azalea Pages: Culture: How To Grow
- Puyallup Research and Extension Center, Washington State University: The Myth of Cloroxed Clippers