When pruning isn't your passion -- and it shouldn't be -- dwarf rhododendrons (Rhododendron spp.) make a smart choice for foundation plantings and other small spaces. Dwarf rhododendrons come in a range of colors, with mature heights from 2 to 5 feet tall, depending on cultivar. The evergreen shrubs only need minor pruning once a year to keep them looking their best, so you can spend your valuable time doing something you really enjoy.
1. About Dwarf Rhododendrons
Dwarf rhododendrons are commonly hybrids. They bloom in the spring with clusters of ruffled flowers, smaller in size and in number per bunch than larger rhododendrons. Cultivars include "Scarlet Wonder" (Rhododendron x "Scarlet Wonder"), which grows 2 feet tall and 3 feet wide in U.S. Department of Agriculture plant hardiness zones 5 through 8, and pink "P.J.M." (Rhododendron x "P.J.M."), which reaches 3 to 5 feet tall and spreads even wider in USDA zones 4 through 8. Aside from hybrids, the species Rhododendron yakushimanum, which grows in USDA zones 5 through 9, reaches 3 feet tall. It has more traditional round flower clusters and cultivars in white, red and pink -- named for Snow White and the Seven Dwarfs.
2. Late Winter to Early Spring
Dwarf rhododendrons bloom in the spring, so any pruning you do in late winter to early spring means sacrificing flowers. Pruning at this time should be in response to a problem, and not an annual event. You can, however, remove any dead or crossing branches, and carefully clip out any flower buds that were blackened by frost -- though only after temperatures are consistently warm. Older dwarf rhododendrons can become leggy, with lose foliage at the base. Late winter to early spring is the time to cut them back to any point -- small-leaf rhododendrons have dormant growth buds all along their stems -- for a rejuvenated plant. After this, though, the plant won't bloom for a season or two.
3. Spring to Late Spring
Once flowers are blooming, feel free to clip back the rare branch that extends farther than you like -- whether it's too tall or too wide -- and take the flowers inside for an arrangement. If the look of the fading flowers bothers you or your plant didn't bloom well, snap off the clusters at the base, being careful not to damage any new growth buds. As growth for next season begins, you can pinch off single growth buds to develop into two buds for a bushier plant. Don't prune your dwarf rhododendron more than 21 days after flowering.
Bypass pruners are sufficient for stems up to 1/2 inch in diameter. You'll need loppers for branches up to 1 1/2 inches wide. Cleaning the blades of pruning tools with household antiseptic cleaner before each use keeps plant diseases and fungus from spreading to your dwarf rhododendron from previously pruned plants. Keep the pruning tools out of reach of children. Rhododendrons are highly toxic if ingested, so avoid planting them where children and pets play unattended. Dispose of clippings where they aren't easily accessed by either.
- The Flowering Shrub Expert; D.G. Hessayon
- Monrovia: Scarlet Wonder Dwarf Rhododendron
- Monrovia: P.J.M. Rhododendron
- National Home Gardening Club: Rhododendrons
- American Rhododendron Association: Pruning and Dead-Heading (Withered Flower Removal)
- The American Rhododendron Association: Rhododendron and Azalea News, Spring 2010
- Centerton Nursery: Pruning and Care of Woody Shrubs Through the Seasons
- University of Tennessee Extension: Best Practices for Pruning Trees, Shrubs and Ground Covers
- University of California Extension: Safe and Poisonous Garden Plants
- Thinkstock/Comstock/Getty Images