Care for Rhododendrons & Azaleas
by Don Janssen, Extension Educator
Rhododendrons and azaleas require little care once they are established. A good heavy mulch will conserve moisture and keep down weeds. No cultivation should be done because the shallow, fine roots are easily damaged.
Avoid using general garden fertilizers for rhododendrons, azaleas and other acid-loving plants. Use those specially formulated for acid-loving plants and follow directions. Fertilizers supplying the ammonium form of nitrogen are best.
Fertilization should be done carefully, or the fine, delicate roots close to the soil surface will be damaged. A fertilizer analysis similar to 6-10-4 applied at 2 pounds per 100 square feet to the soil surface is usually adequate.
Fertilizing should be done in May, but do not fertilize after July 1. Late summer fertilization may force new growth that will be killed by the winter.
Soil acidity must be maintained to ensure good growth. If the soil pH is above 5.5, apply iron sulfate or agricultural sulfur to the surface of the soil. The amount to apply will depend on the existing pH, but in all cases apply only a small amount at any one time.
The thickness of the mulch (2-3 inches) must be maintained. As the old mulch decomposes, add new mulch. This is best done in the late fall.
Many rhododendrons have been killed by overwatering in sites where drainage is bad. Check the soil before watering. Avoid excessive irrigation in fall. Plants kept dry in September will tend to harden off and be better prepared for the winter. If the fall has been excessively dry, watering should be done after the first killing frost.
There is little need for pruning azaleas and rhododendrons. If growth becomes excessive, reduce the size with light pruning. It is important to remove the flower stems on rhododendrons as soon as flowering is complete. Failure to do this will reduce flowering the following year. Break out only the dead flower cluster, not the young buds clustered at its base.
The two winter enemies of evergreen rhododendrons and azaleas are sun and cold wind. If hardy types are selected and proper planting locations are chosen, little or no winter protection is needed. If existing varieties show winter damage, provide some protection. Donï¿½t be alarmed when leaves curl and droop on cold days; that is normal.
University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office