The rhododendron has strict cultivation requirements. When first planted, proper site selection and subsequent care of the plant will ensure blossoming. With more then 700 rhododendron varieties and thousands of cultivars, a gardener has a diverse range of choices in flower color, shrub sizes and flowering times. Once established the plant is hardy and tolerant of weather fluctuations.
Rhododendrons grow best in partial shade but will tolerate full sunlight. Planting areas that offer full shade will cause the shrub to not bloom and attain only weak growth. Avoid early morning sunlight in cold regions where the ground often freezes. The sunlight will heat up the water on the plant's foliage and buds. This causes desiccation to occur because of the roots' inability to supply the plant with water. The small, forming flower buds will dry up and fall from the shrub or blossoming will be severely limited.
The rhododendron prefers acidic soil with a pH of 4.5 to 6.0. Soil high in humus supplies much-needed nutrients to the shrub. Adding organic matter such as compost, aged manure or peat moss benefits the rhododendron at the time of planting.
The rhododendron is susceptible to windy locations. The brittle stems will often break and the shrub will be defoliated in heavy winds. Often blossoming will be limited as the delicate flowers are torn from the plant. Choose a sheltered location to plant the rhododendron. Against a building or fence-line is ideal. Choose a north, east or west building side to plant against. Avoid planting under eaves where a steady runoff of water will damage the plant and flowers. Standing water can also make the root system of the rhododendron rot.
Bud formation begins during the summer and fall months and continues through winter on the old wood of the shrub. The months of March, April and May are the peak months for rhododendron shrubs to flower. Shrubs planted the previous year will easily flower during this time period for the first time.
Once flowering ceases, the rhododendron will benefit from prompt removal of the flower heads. Clip or snap them and discard. Removal helps to prevent the plant from forming an abundance of seeds. If the shrub forms excessive amounts of seeds. the following years flowering will be severely limited.