The larger leaves the evergreen rhododendron has, the shadier location will it require. The small-leaved evergreen rhododendrons adapt well, grown in exposed locations, as long as they receive ample moisture. Deciduous rhododendrons feel comfortable growing in open, sunny positions. Although the leaves of Catawba rhododendron (Rhododendron catawbiense) and Rhododendron smirnowii are evergreen and large, they can take quite a lot of sun, provided they get sufficient moisture. In the wild they usually grow on the edges of moist, deciduous forests, in blazing sunshine, yet in damp soil. The native habitat of Rhododendron caucasicum is high in the Caucasus mountains, where large groves flower profusely every year in full sun. The rhododendrons of this species flourish in similar conditions in our gardens, too.
[banner] Several species of rhododendrons (Rhododendron degronianum ssp. yakushimanum, Rhododendron decorum, Rhododendron ponticum, etc.) are native to the areas, where damp and cool period is far longer than the sunny period. The plants of these species feel more comfortable planted in light shade in our climate.
Rhododendrons, which receive sufficient light, grow stronger, set more flower buds, and are less vulnerable to winter freeze, diseases and pests. When grown in full shade, their shoots grow lanky, the leaves become sparse and they flower less. On the other hand, too much sunlight will cause their leaves to turn yellow, and numerous brown spots will appear along the veins and the edges of the leaves.
The evergreen large-leaved rhododendrons are best planted on the north side of buildings, in a sheltered position. The areas on the east and west sides are also suitable, since these locations are shaded for a part of the day. The rhododendrons set the flower buds for the next year in summer. In our climate, this usually occurs in July or August, so plenty of water and sunlight are essential during this period.
To provide rhododendrons with light shade, plant them adjacent to the trees and taller shrubs. Any plants with deep roots make good neighbours for rhododendrons. Large trees with surface roots will inhibit growth of rhododendrons with their shallow roots, and they will go into decline. Rhododendrons dislike being planted near any species of limes, beeches, poplars, bird cherries and maples. Crowns of these large deciduous trees are very dense, which subjects rhododendrons to an unwelcome protection from rain.
Rhododendrons grow well alongside pines, hemlocks, fir, oaks and other deep-rooted trees. Since all rhododendron species need varying light levels, there is a variety to suit any location – sunny, semi-shaded or fully shaded. Evergreen large-leaved rhododendrons will grow well in semi-shade; deciduous varieties with small leaves will tolerate exposed sunny conditions, but prefer cool semi-shade; and deciduous rhododendrons are best planted in open sunny locations, but will adapt to growing in light shade.