How to Prune & Care for a Rhododendron

You'll find over 10,000 varieties of rhododendron.

With over 10,000 registered varieties of rhododendron, from large-leaved to dwarf shrubs, you'll find one for every climate in the world, but they all need similar care. Both the evergreen and deciduous rhododendron need little pruning in early spring, and only to maintain their size, encourage blooming and remove dead, broken and diseased twigs. But they have specific requirements in other areas, including fertilization, irrigation and winterization, that you must meet for them to continue to reward you with their showy blooms.

Things You'll Need

• Shears
• Compost
• Agricultural sulfur
• Iron sulfate
• 6-10-4 fertilizer
• Mulch
• Water
• Burlap

Instructions

Pruning

1. Pinch the tips of young shrubs to make them bushy.

2. Cut long branches on a mature plant back to a side branch. Use this method to train your shrub into the shape you want it to have.

3. Remove the flower stems when the blooms fade. Take out the dead flower cluster without disturbing the young buds already at its base, ready for next year.

Additional Care

1. Choose a planting site with afternoon shade in an area protected from the wind, such as a slope.

2. Mix a 4-inch layer of compost with the topsoil to a depth of 1 foot. Rhododendrons need rich soil that also drains well. Root rot occurs if their roots stand in water.

3. Take a sample of your soil to your extension office for a pH test. Rhododendron bushes need acidic soil with a pH of 5.0 to 5.5.

4. Amend the soil's pH if necessary. Use either agricultural sulfur or iron sulfate to lower its pH. The amount of amendment will depend on your soil's exact pH.

5. Apply a 6-10-4 fertilizer to the soil as the rhododendron's buds swell in early spring. Use 2 pounds per 100 square feet. Water thoroughly and keep the plant moist through the growing season.

6. Mulch your rhododendron's root area to conserve moisture and reduce weeds in the growing season. In winter, mulch it to protect the roots from the freezing weather.

7. Winterize your shrub. Withhold water in September so it can harden off for the winter. Water it again in late November. Cover your rhododendron with burlap to protect it from the cold and wind.

8. Treat diseases as soon as you notice them. Rhododendrons are susceptible to scorch and chlorosis.

9. Control pests. Ask your local extension office for help identifying and finding a solution for bug infestations.

References

• "Sunset Western Garden Book"; Kathleen Norris Brenzel; 2001
• University of Missouri Extension: Growing Azaleas and Rhododendrons

Resources

• Oregon State Extension: Azalea and Rhododendron Care and Culture