Robert Furniss, Portland, OR
Reprinted from Portland Newsletter
Rhododendrons need company - some for shade and protection from wind, some for diversity of form and texture, and some for off-season color and interest.
Companions the world around may be good or bad. In some situations the good may turn bad, and vice versa. None is perfect. So it is with plants associated with rhododendrons. Selecting and maintaining the right combination in a particular garden is an exercise in ingenuity.
Companion plants should: Fit the site and the purpose, thrive under conditions favorable for rhododendrons, and provide contrasting texture or color. They should not compete excessively for food or moisture, nor in beauty during the blooming season. They should not harbor insects nor diseases that spread to rhododendrons.
The home gardener's need for companions for rhododendrons is different from that of gardeners in parks, arboreta, and large estates. On a city lot space is at a premium. The city gardener must think small. Here are some suggestions from one who has.
Go easy on ground covers that compete with shallow-rooted rhododendrons and require frequent meticulous care. Judicious use of Gaultheria, Juniperus, kinnikinnic, hardy cyclamen, and a few others is sufficient for a pleasing effect in well-mulched beds.
For interplanting or nearby grouping, Corylopsis, Enkianthus, Euonymus, Garrya, Hamamelis, Kalmia, Oxydendrum, Pieris and Vaccinium all contain good shrubby species.
To provide light shade or variety, the following small trees and large shrubs are useful: Acer circinatum, A. palmatum, Cercidiphyllum, Chamaecyparis obtusa, Corpus kousa, Cupressus bakeri, Halesia caroling, Magnolia, Nyssa sylvatica, Pinus contorta, Stewartia, Styrax japonicus and Tsuga mertensiana.
Some words of caution. Douglas fir and western red cedar compete heavily for moisture and light. White birch roots are invasive and the leaves harbor aphids that weep honeydew. Ornamental cherries sucker profusely and host caterpillars that spread to rhododendrons. Maples often die of Verticillium wilt. Magnolias have massive root systems and cast dense shade.