Date: August 20, 1998

Native Evergreen Rhododendrons

Dick Bir
NC State University

Three species of evergreen rhododendron are native to the state of North Carolina. All are easily seen in the mountains but are less common in the Piedmont.

Rhododendron minus exists as two botanical varieties, carolinianum and minus. Both are commonly called Carolina rhododendron while variety carolinianum is sometimes called punctatum or deer tongue laurel in mountain communitites. Minus has the smallest leaves and smallest flowers of the native rhododendron species. Flowers of carolinianum appear the earliest in spring of all native evergreen rhododendron species, often in early April in the Asheville area just as new foliage is expanding on the same plant. Variety minus waits until new growth is fully expanded before flowering, often being in full bloom about Father's Day in the Brevard area. The most common flower color is a pale lavendar pink but darker purples and white forms do exist. The most intensely colored flowers in this species are often at higher elevations while the population surrounding Linville Gorge has a distinctively pink coloration.

Rhododendron catawbiense is probably the most famous of North Carolina's native evergreen rhododendrons due to the incredible annual floral displays along the Blue Ridge Parkway, particularly at Craggy Gardens and in the acres of natural gardens atop Roan Mt. on the Tennessee border. Acres of raspberry sherbert colored flowers have the world believing this is the only color available in this species but it is not. The Catawba rhododendron can display flowers in pale pink as well as white, with a wonderful population found under tall shade trees and nestled among boulders at Hanging Rock State park and another population of purple and pink flowered plants at Pilot Mountain State Park, both in the NC piedmont.

While most abundantly found on or near high mountain balds and the bluffs of places like Grandfather Mountain, R. catawbiense exists in significant native populations well into the NC piedmont with significant groups at Flower Hill east of Raleigh and at the Hunt Arboretum of the NC Botanical Garden in Chapel Hill. The difference, as with so many native shrubs, is that they thrive in full sun in the mountains above an elevation of 3000 ft. but are found in shaded ravines under tall trees or on east or north facing slopes in the warmer Piedmont. Gardeners should pay attention to these differences in natural habitat as evergreen rhododendrons planted on poorly drained soils or in full sun in the NC Piedmont are destined to fail.

Flower time varies with weather and elevation. Plants at lower elevations can be expected to flower around Mothers Day and sometimes before while the Rhododendron Festival in Bakersville, at the base of Roan Mountain, is usually scheduled around Memorial Day with peak bloom atop the mountain often the first week in June but in the cool spring of 1997 peak bloom did not occur until almost July. Fortunately, those planning a trip to see the wild rhododendrons in flower can usually get on the Blue Ridge Parkway in late May and, by the time they reach the top of Mount Mitchell, will have driven through an elevation where Rhododendron catawbiense is at it's peak bloom as well as seeing mountain laurels, flame azaleas and scores of different wildflowers.

Rhododendron maximum is usually the most striking plant of the three NC native evergreen rhododendrons because of it's overall size and the large dark green foliage. Leaves are commonly ten inches long. Many plants are tall enough that I can easily walk through Rhododendron tunnels . . . I am 6 ft. 2 inches tall . . . where they occur near Mount Pisgah and elsewhere throughout the eastern United States. Specimens twenty-five feet tall exist in the upper piedmont and mountains of NC.

Commonly called max or rosebay, this big native rhododendron is almost always found growing in the shade or at the edge of the woods with impressive natural groups along the entrance road to the NC Arboretum in Asheville. Flower color is almost always white, often with a yellow throat on individual flowers. Beautiful pale pink forms are commonly seen in the higher mountains but when these have been transplanted to lower elevations they tend to flower white. The intensity of pink color seems to be due to cooler temperatures.

R. maximum's time of flowering varies due to weather but when max comes into bloom in NC it usually flowers along the entire range within a few days so you could see them in flower in Asheville, fly to New England, and see max in flower in the Berkshires the same week as I have. Regardless of when it flowers, it is almost always starting to flower after R. catawbiense has finished so in the cool spring of 1997 max peaked in late July around Cashiers.

In the garden these natives will perform well if attention is paid to where they grow naturally. To have the best, healthiest plants those gardening anywhere except the highest mountains should plant all of these evergreen species in at least partial shade. Morning sun and afternoon shade are best in the west. High pine shade similar to that favoring azaleas provides the best sun situation as rhododendrons move east in NC.

Good soil drainage is absolutely essential throughout the range but becomes increasingly important in areas where soils are warm for longer periods of time. These warmer soils and poor drainage favor the fungal organism Phytophthora cinnamomi, which causes the root rot which is lethal to these rhododendrons. In addition, those planting evergreen rhododendrons should have their soil tested before planting, add sufficient phosphorus from superphosphate or a natural source to provide for adequate root growth, then dig a wide, shallow planting bed, amend mineral soils with 3 to 4 inches of pine bark mulch by thoroughly mixing the pine bark with the planting soil, plant the rhododendron no deeper than it was growing in the nursery or slightly shallower, mulch with pine needles, bark, shredded leaves or yard compost and do not allow the plants to dry out the first couple of years they are in the soil. In many areas, irrigation will not ever be needed but until a rhododendron is established, moist but not wet soils are best.

Finding these native evergreen rhododendrons in garden centers may be next to impossible in some areas. Therefore, if you want them in your garden you may have to find some descendents from our native wild plants which are sold as hybrids. There is a growing group of rhododendron fanciers that think some of the alleged hybrids are just selections of superior wild plants that were made 50 to 100 years ago and have come to be called hybrids.

The most common substitutes or look alikes for Rhododendron minus are the PJM hybrids which originated at Weston Nurseries in Massachusetts. Ed Mezitt, the father of this line, used natives from the Blue Ridge mountains as some of the parents of his hybrids. 'PJM' itself has darker purple flowers than most of our natives but 'Olga' is more pink while 'Pink Diamond' has rose colored flowers. All of the PJM hybrids do best in the western piedmont and the mountains.

Substitutes for Rhdodendron catawbiense are easy to find in almost any spring garden center. 'Roseum elegans' and 'English Roseum' are the most common but others abound. Substitutes for Rhododendron maximum are easier to find if you are just looking for a white flowered evergreen rhododendron. 'Catawbiense alba' or 'Cat alba' is relatively easy to find but most white flowering hybrids do not have the large foliage or overall size of the native. Fortunately, max is among the easiest of the natives to find available from nurseries. They may not be obvious in your garden center but if you ask your local garden center or landscaper to find some for you, they probably can.

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