Rhododendron That Doesn’t Flower

Question

There’s 10 years I moved to my house, and two huge evergreen rhododendrons (that are becoming a pain to to trim) siding the front door only produced 1 flower each, in May of 2017 as the photo shows, weirdly at the same time and in the same position in the round, 7-8 feet tall plants. What are they missing? Something in the soil, lack of sunlight? They seem to be thriving as is, they grow too fast already. The whole front yard is shaded by large trees, there’s very little sun getting through in the afternoon.

Answer 1

All rhododendrons and azaleas will grow well in light shade. Most rhododendrons including the Carolina rhododendron will bloom more abundantly in full sun if the soil is kept moist, but sunscald and winter desiccation problems may cause foliage and bud problems. More sun stimulates flowering and but may trigger lace bug infestations. In hot climates or in windy places partial shade is usually mandatory. Also, full sunlight tends to bleach the flowers. In cold climates, most rhododendrons do better on the north side of a building or on a northwest slope where they receive summer sun but protection from the winter sun. All rhododendrons and azaleas need some sun for best flowering but in general require partial shade. These requirements vary between varieties and also vary in different climatic zones. Re blooming… this could be a failure to set flower buds or failure to open the flower buds. Failure to set flower buds may be a sign of too much health and vigor in a plant. One solution my be to prune the roots by cutting around the plant with a spade or moving the plant. This will check foliage growth and encourage production of flower buds. Application of nitrogen rich fertilizers is the main cause of vigor which suppresses flower bud production. Deadheading flowers as soon as they wilt can promote flower bud production. Too much shade, a cool wet summer, or inadequate phosphorus or potassium in the soil may also suppress flower bud production. There are a number of other reasons for a lack of flowers. The effect of each variable depends upon the variety of the plant: pruning after they produced flower buds a few weeks after they stop opening blooms in spring; some rhododendrons that come from the seed of a hybrid plant will look good but will never produce flowers or will produce very poor flowers; cold weather killed the buds (the buds turn brown); some rhododendrons need full sun to bloom and others can take fairly dense shade; more shade produces tall spindly foliage and less flowers. You can usually tell when the plant has ever bloomed. A rhododendron that has bloomed will have the seed pods on it unless it has been dead-headed. If dead-headed too late after blooming, new flower buds can be damaged.