Rhododendrons

Rhododendrons are one of the most popular flowering shrubs available in the home landscape, and for good reason; they have beautiful striking flowers that are found in rich colors that begin to bloom in early spring and last until early summer.

Rhododendrons are either evergreen or deciduous plants.  Their blooms bear a strong resemblance to Azaleas, in fact, they are in the same family. Rhododendrons can vary greatly in size from dwarf shrubs to over 30 feet tall!  There are 26 species that are native to North America. Rhododendrons are toxic if ingested, so be sure to keep a close eye on pets and children when around the plants.

Culture

Rhododendrons need acidic-based soil to perform well. They prefer some light shade and should be in a place that protects them from direct sun during midday. Too much direct sun and heat can cause leaf wilting and drop. Strong winds and too much direct sunlight will cause poor growth. Soil type should be well drained, moist, with  a Ph of about 5.5.  Be cautious of planting your Rhododendron too close to your home foundation or other cement area as there is often a lot of lime which raises the ph to levels unacceptable for good growth. To confirm, check the soil for the level of acidity/alkalinity. If the soil is too alkaline,  consider planting in another location.

Care

Pruning and pinching young Rhododendrons will help promote full, bushy growth and encourage blooming. Pruning should be done in the early spring. Pruning well-established plants may prevent blooming for the next few years so if you are anxious for those spring blooms each year, you can forego pruning altogether and let your plant take its natural shape. Cold, bitter winters and strong winter winds can severely damage Rhododendrons, so covering for protection is a good idea. You can use burlap, mulch or other organic matter.

Diseases and Pests

Rhododendrons can be susceptible to mealy bugs; applying dormant oil in the winter can prevent these.

Purplish markings on your Rhododendron probably mean powdery mildew that has been  especially found in the Pacific Northwest for the past few years. There are sprays that help solve the problem.

Cultural practices can also prevent mildew such as choosing a location with good circulation and avoiding crowding of plants. The time to control mildew chemically is when the leaves begin to emerge, usually at or just after spring flowering. Apply the sprays, alternating types, at 2-3 week intervals, until the infection period is over. Make sure to completely remove the infected leaves and dispose of to avoid cross-contamination or re-infection.