Shade Tolerant RhododendronsShade Tolerant RhododendronsRhododendrons and azaleas, which are among the most popular flowering plants for shade, are commonly thought to be, as a group, amenable to low-light conditions. In fact, all of them need some sun to produce the most profuse flowers, but some need more sun than others. In general, most Azaleas will grow very well if they receive four hours or more of bright sun per day. Rhododendrons will grow nicely in full sun to moderate shade. A few Rhododendron varieties such as 'Caroline', 'Scintillation', Yakushimanum hybrids, 'Hong Kong' and the hardy varieties from Finland must have some shade in midday or the foliage will yellow or even burn - especially during a hot summer. 'P.J.M.' and 'Nova Zembla' are two of the hardiest evergreen types.
Many varieties need shade to prevent lace bug infestations since the natural enemies of lace bugs are not active in sunny areas.
On the other hand, if shade is too dense, it can cause fewer blooms and spindly growth. Dense shade and poor air circulation can also be deadly to Rhododendrons. The combination frequently results in fungus which attacks new plant growth and eats away at the plant branch by branch. The species and hybrids listed here bloom especially well in the minimal sun and bright light of open to medium shade, and two of them, 'Snowlady' and the royal azalea, will even bloom in deep shade. Despite their physical differences, rhododendrons and azaleas belong to the same genus and require the same growing conditions. The rhododendrons are all evergreen; ten of the azaleas are deciduous and one is evergreen. [Return to Top]
'Boule de Neige' means “Ball of Snow” in French. As you might expect, the flowers are white, in perfect rounded trusses, and geometrically proportioned to the leaves. The habit is dome shaped. Leaves are matte green, and the plant’s constitution is tough and very hardy. It grows to a height of 4' and width of 5'. It even blooms well in deep shade.
'Bow Bells' is a perfect mound of pink. The flowers are followed by shiny, copper colored new leaves. As the season progresses, the mound becomes a superb jade green with rose-red bud scales for another show of color. While growth at 10 years is 3', it will become a larger plant, so give it enough space. A site with filtered light is best for ´Bow Bells´. Fertilize lightly, as an excess of fertilizer will cause foliage burn more easily than on most rhododendrons. [Return to Top]
'Elviira' rhododendron is very hardy. It grows to a height of 2' and width of 18" to 24". It grows well in shade. A very low growing rhododendron cultivar. Densely branched, it is covered with flower buds that are hardy to -30F and open bright red. From the group of Marjatta hybrids developed at the University of Helsinki, Finland. [Return to Top]
'King George' is a tall hybrid rhododendron that blooms in mid-spring, producing huge pale pink flower clusters that turn white as they mature. It generally grows 6 feet tall but may reach a height of 12 feet. With rhododendrons, the rule of thumb is that the larger the leaf, the less sun they can handle gracefully. 'King George' and other Loderi rhododendrons are large leaf plants that follow this rule. However, if given enough shade they are also drought tolerant. [Return to Top]
'Nova Zembla' rhododendron has true hardiness in a red. A vigorous plant that has good foliage and will grow in more difficult areas. This hybrid exhibits some outstanding characteristics. Of course, hardiness tops the list. A nice looking contrast with other plants. Extremely showy, red flowers make a real display in the spring.. Dark red flowers in a ball-shaped cluster. Broad, bushy plant. Cold and heat tolerant and sun and shade tolerant. It grows to 5' tall and is hardy. [Return to Top]
'P.J.M'. hybrid rhododendrons. The 'P.J.M.' group of rhododendrons are smaller, growing to a height of 3 to 5 feet tall. Form is rounded and the foliage is leathery and dark green until fall when it turns almost purplish. One of the reasons the 'P.J.M.' group is such a heavy flowerer is that the plant does not set seed. They are very hardy, among the hardiest and most shade tolerant rhododendrons. They include the following:
'Ramapo' is a good dwarf rhododendron. It grows approximately 2 feet tall and 4 feet wide. Flowers are bright violet-pink. 'Ramapo' is hardy to -25°F. Tolerates sun and shade. [Return to Top]
'Snowlady' is a hybrid rhododendron that grows to a height of only 30 inches. It produces an abundance of snowy white flowers and has fuzzy green leaves. [Return to Top]
Rhododendron carolinianum, the Carolina rhododendron, is a native American plant that grows wild in the Blue Ridge Mountains of North Carolina. It is 3 to 6 feet high with a naturally rounded shape and dark green leaves 3 inches long. In mid-spring it is covered with 3-inch clusters of rose-pink flowers. There is also a variety with pure white flowers and lighter green leaves, R. carolinianum 'Album'. It wants bright shade or dappled sunlight, but by no means deep shade. [Return to Top]
Rhododendron catawbiense, the Catawba Rhododendron, is an evergreen shrub that grows to a height of 6 or 10 feet tall and a width of 5 to 8 feet. Though unusual, some cultivars may reach 15 or 20 feet with age. Foliage is dark green and leathery, with oval leaves, lending a course texture to the landscape. Flowers range in color from lilac to rose with green or brown markings in the throat. This plant is very hardy. It is generally dense under ideal conditions, but becomes more open in dense shade. [Return to Top]
Rhododendron calendulaceum, the flame azalea, is a native American species, growing 4 to 6 feet high. It bears clusters of 2-inch clove-scented yellow to red-orange flowers in early summer, when most other azalea species have finished blooming. The leaves are 3 inches long and drop in the fall. Does best with partial shade. [Return to Top]
Rhododendron kuisianum, the Kyushu azalea, is a low-growing Japanese species, only 18 inches high. Its leaves are deciduous when the plant is young but evergreen in maturity, remaining on the plant all winter, though often changing color. In its original form the Kyushu azalea is covered in mid-spring with 8- to 10-inch clusters of lilac pink flowers, but there are many named hybrids derived from this species.
It prefers partial shade. [Return to Top]
Rhododendron schlippenbachii, the royal azalea, is a deciduous species, also of Japanese origin. It has soft green leaves that grow in whorls around the stem and turn yellow, orange and crimson in the fall. Its pink star-shaped flowers bloom in loose clusters in mid-spring and have a delicate fragrance. It needs shade from hot sun. Dappled shade or morning sun/ afternoon shade is necessary to protect the rather thin textured leaves from scorching. [Return to Top]
Other deciduous azaleas: Most deciduous azaleas do well in full sun and frequently are poor bloomers in the shade. "Maid in the Shade" deciduous azaleas is a collection of deciduous azaleas compiled by Transplant Nursery selected to do well in shadier locations. They include:
The larger rhododendrons and azaleas like 'King George' and flame azalea make excellent specimen plants or informal groups in woodland settings, while smaller plants, such as the Carolina rhododendron, flourish in the shade of arbors and trellises. 'Snowlady', and Kyushu azaleas can be used in the foreground of border plantings, and all three are also handsome pot plants for use in tubs or containers on shaded patios and terraces. [Return to Top]
Royal azalea is hardy in Zones 4-8, to -25° F; flame and Kyushu azaleas and Carolina rhododendron in Zones 5-8, to -15° F; and 'King George', 'Snowlady' and R. williamsianum in Zones 7 and 8, to +5° F.
All rhododendrons thrive in a cool, moist, acid soil. Plant them in spring or fall where winter damage is no hazard; otherwise, plant them only in spring, setting the balled-and-burlaped root balls in the soil no deeper than 12 inches. Do not fertilize at the time of planting, as this might injure the roots, but water deeply. Supplemental feeding later is not normally needed, but if a plant appears pale or droopy, apply cottonseed meal or a fertilizer for acid-loving plants around its base in early spring. A year-round mulch of rotted oak leaves will also provide natural nutrients and will help keep the soil cool and moist.
Do not cultivate around the shallow roots of rhododendrons and azaleas, but pinch off their faded flowers to improve bloom the following year. Also, prune out dead, diseased or damaged branches, and cut old branches back to the soil level to encourage new growth.
Rhododendrons may be propagated from stem cuttings of new growth taken in late summer and rooted in a mixture of perlite or vermiculite and peat moss. For deciduous azaleas, cuttings may need bottom warmth of 75° and artificial light to promote root growth.
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