Some Thoughts on Growing Evergreen Azaleas

by Sally Perkins

Rhododendron kaempferi in Andover Bird Sanctuary
Picture by S & J Perkins
Rhododendron kaempferi growing in Andover, MA

Evergreen azaleas are one of those pleasant memories I have from my childhood days in Maryland. Anyone could grow evergreen azaleas as long as they were not against the cement foundation that leached lime and caused chlorosis. Most people had mounds of azaleas in various shades of screaming red, shocking pink, and icicle white with the occasional purplish or bicolor effect. Unfortunately, most of the evergreen azaleas do not bloom reliably in Salem, New Hampshire. I have had to be a little more selective (or maybe less so) trying those that have had a modicum of success in warmer areas in Massachusetts. Here is where I listen intensely to the idle chatter at ARS Mass. Chapter Plants For Members work days in Portsmouth, Rhode Island. The 'amateurs' that contribute cuttings, stick cuttings, and pot them up are very knowledgeable beyond any book on the subject. I sometimes feel like a student following and listening to professors at college.

When dealing with marginally hardy plants, site selection is everything. An unhealthy plant is very unlikely to make it through the long New Hampshire winters. Rhododendrons may lose half their roots during a typical winter. A little more protection from sun, wind and freezing and thawing may be the difference between a nice bloom and a brown stick in the ground come spring. For example, the particularly severe summer drought in 1995 resulted in poor root growth during the critical growing season and many flower buds blasted despite a higher minimum temperature than predicted by reference books.

Perhaps because of reduced wind close to the ground, low growing evergreen azaleas seem to do better. 'Michael Hill' is such a plant that acts like a ground cover on a steep hillside. It is a North Tisbury R. nakaharai hybrid from Polly Hill and I have tried a few others North Tisburys but they have not really taken off yet. I do grow the species R. nakaharai in a couple of forms. One that I like is 'Mt. Seven Stars' that stays flat to the ground with red-orange blooms in mid to late June. A more upright plant, almost rose red with a red flare, is 'Bovee's form' from the Oregon nursery of that name blooming in mid-June. The late Dr. Schroeder had a breeding program for hardy evergreen azaleas and we selected from Holly Hills' catalog a few dwarfer hybrids in a variety of colors. 'Holly's Late Pink' is a semi-double low mound blooming in the first week of June. John's favorite Schroeder azalea is 'Dr. James Dipple'(salmon orange) but it put on a poor showing after the drought of `95 and lost some merit in his eyes. 'Moby Dick' with huge white blossoms succumbed to a virus infection but I know other ARS members growing it well. Other Schroeders that have bloomed more or less consistently are 'Margaret Hyatt'(a double lavender), 'Hoosier Peach'(small pink flowers) and 'Lavender Mist'(purple). There are still many evergreen azaleas rated -15 or more that I have not tried.

R. yeodense var.poukhanense seems to be reliable for me. I grow it in half to 3/4 shade so it tends to have an open habit. I have a particularly large flowered purple one that has always performed well (it may be a hybrid). The pink form I have has smaller flowers and always looks misshapen. We moved it to the edge of a wooded area in my neighbor's yard and it looks perfect in that setting. Sometimes you just have to find the right place before a plant really shines. R. yeodense is a garden form with double flowers. I do not have it but I keep an eye out for it anyway. Many of the hardier evergreen azalea hybrids have some R. yeodense var. poukhanense parentage.

R. kiusianum is my current rave in evergreen azaleas and this should keep me busy for many years. The Japanese have been selecting forms so that there is considerable variability especially because of natural hybridization with R. kaempferi. I do not let it bother me that some books rate R. kiusianum zone 7a and -15 in others or that they are almost deciduous here. R. kiusianum is such an endearing species with small leaves and a fine texture that stays low, almost prostrate in form. I do not give them full sun and have been admonished that they would look more compact if I did. It seems to me when I try full sun on young plants they turn into brown sticks in the ground. Blooming in late May, the white form album, 'Komo Kulshan', 'Benisuzume', 'Pink Clusters', and 'Mountain Gem' have all been good.

I must confess that R. kaempferi is a species that if I had more room, I would have more plants. Native to Japan, in zone 5 it is nearly deciduous and like R. kiusianum winters over only the cluster of small, thick summer leaves. Rated the hardiest evergreen azalea, R. kaempferi unfortunately, grows upright 8-10 FEET making it difficult for me to find a space for it on my small property. Better to visit the R. kaempferi collection at the Arnold Arboretum with its impressive display in early to mid-May. Even more color variations with pinks, salmons, and reds occur on the grounds of the Andover Bird Sanctuary in Massachusetts. The redder forms seem to have better fall color which is a bonus here in New England where fall color is so spectacular.

One of John's favorite species is R. semibarbatum. This species is not an evergreen azalea but a collector's plant that is so unique it gets its own section in the Rhododendron genus. This deciduous species is rated zone 7 but varies in hardiness. Our plant was a seedling from the Arnold Arboretum Case Estate Sale and points out that seedlings of a variable species may just turn out to have more hardiness. It blooms in early July with small 3/4 inch white flowers hidden below the fully expanded leaves. Two stamens are very HAIRY and different from the other three (something a botanist finds interesting). It has a nice upright architectural habit. Again fall color makes it special in New England .

For more information Fred Galle's book "Azaleas" is a good reference for both evergreen and deciduous azaleas.

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