Companion Plants for Rhododendrons and Azaleas
J. Patrick Tatum, Terre Haute, IN
Reprinted from Indiana Chapter Newsletter
All of the gardens of the members of our chapter that this author has ever visited contain many different companion plants. However the "sameness" of these plants from one garden to another is rather obvious. This is not really a criticism of the gardens and their owners but nevertheless this state of affairs does not have to exist. Therefore for a number of years I have tried to broaden the diversity of plant material in my garden.
Vaccinium vitis-idaea (Lingonberry) - Heat, cold and sun tolerant. Grows about 1' tall. Stoloniferous. Outstanding foliage plant. Flowers are white and in the fall it will bear small red berries which birds do not seem to like. These berries are edible but should be cooked first. Flowers early.
Vaccinium vitis-idaea minus (Mountain Cranberry). Just a smaller growing form of the species above. Flowers are apple-blossom pink. Slower to flower than the larger growing form. New growth is copper colored and very striking. Heat, cold and sun tolerant. Foliage turns a deep mahogany color during the winter. Strongly stoloniferous. Flowers early. A ground cover.
Vaccinium oxycoccus (Small or European Cranberry). Heat, cold and sun tolerant. Slower to flower but it is evergreen although the foliage turns a deep mahogany color during the winter. Plant stems root themselves as it grows across the ground. Foliage color is not as good as V. vitis-idaea minus. Growth is rather informal. A ground cover.
Vaccinium macrocarpum "Hamilton" (Large or American Cranberry). Heat, cold and sun tolerant. Flowers are apple-blossom pink. Leaves are oval shaped, almost round, but the plant is deciduous. This species is the commercial cranberry of this country but this variety has no agricultural importance. Flowers appear late in Spring, are very small and white with pink stripes. A ground cover.
Calluna vulgaris (Heather). Heat, cold and sun tolerant. Evergreen although some varieties will turn a deep mahogany color in the fall. Comes into bloom about the middle of July and will certainly still be in bloom until Thanksgiving; easily the longest blooming period of any plant this author knows of. Many varieties are available but this author prefers Mrs. R.H. Gray for its outstanding foliage color. Trouble free.
Arctostaphylos uva-ursi (Bearberry). Heat, cold and sun tolerant. The only variety that has succeeded for me is Vulcan's Peak, which has oval, almost round leaves. A ground cover. Stems root as they grow across the ground. This plant is a more dense grower than V. oxycoccus.
Erica tetralix (Heath). Heat, cold and sun tolerant. Easily the best performing species of heath this author has tried. Most varieties of Erica carnea do not have enough heat tolerance for this area. The other species of Erica do not have sufficient cold hardiness.
Gaultheria procumbens (Wintergreen) - Native to much of eastern North America. Heat and cold tolerant and will tolerate at least one-half of a day of full sun in Terre Haute, IN. Ground cover. New growth is copper colored and the new stolons are bright red. Strongly stoloniferous. Flowers are white and the berries are bright red. Trouble free plant. According to the girls in my neighborhood it is my best looking plant, all things considered, which is really saying something since I also grow the Rhododendron Paul R. Bosely and the evergreen azalea May Belle among other things. Outstanding foliage plant.
Kalmia angustifolia (Lambskill or Sheep Laurel). A smaller growing relative of mountain laurel, Kalmia latýfolia. The flowers are dark pink. The form alba does not have white flowers but light pink flowers. Excellent cold tolerance. Slow grower. Blooms late; about the same time as K. latlfolia.
Arcterica nana. A rare plant in cultivation. Extreme cold tolerance and it can tolerate our summers in a shady, cool location. Flowers are white. You have to see it to believe it. Slow grower. A ground cover. Leaves are tiny. Stoloniferous. Early and prolific bloomer.
Bruckenthalia spiculifolia. A close relative of Erica. Heat, cold and sun tolerant. Blooms late May to early June. Flowers are pink. Doesn't stay in bloom as long as Erica or Calluna. Prolific bloomer. Grows about 10" tall but spreads much wider.
Pieris japonica. Heat, cold and sun tolerant. Blooms early. Magnificent foliage plant. Many varieties available including a number of dwarfs. However, the dwarfs are not as cold hardy as the larger growing varieties and are slow to flower, if they flower at all. Every garden should have at least one P. japonica, my personal opinion.
Spirea bullata. Heat, cold and sun tolerant. Deciduous. Flowers are dark pink. Similar to Spirea japonica but much smaller. Blooms off-and-on all summer. Trouble free plant.
Mahonia nervosa. Heat and cold tolerant. Outstanding foliage plant. Slow grower. The winter foliage is a deep mahogany color. Slow to flower; in fact my plant has never flowered since I have had it, about 7 years.
Mahonia repens. Heat and cold tolerant. Even smaller growing than is M. nervosa. Not as good a foliage plant as M. nervosa.
Leucothoe fontanesiana "Nana". Outstanding foliage plant. A rare plant in cultivation. Slow grower. Heat and cold tolerant.
Leucothoe fontanesiana "Girard Rainbow". Outstanding foliage plant. No plant was better named. New foliage progresses through red, copper, yellow and green. Needs to be severely pruned every year or two. Flowers are white. The winter sun can burn the foliage badly. Prolific bloomer. Heat and cold tolerant.
Kalmiopsis leachiana Umpqua Form. A very rare plant in cultivation or the wild. Said to be hard to grow but does well for me. Slow grower.
Mitchella repens (Partridge Berry). Heat and cold tolerant. Ground cover. Stems root as they grow across the ground. Flowers are small, white and star shaped. Berries are red. Doesn't like dense shade.
Ledum groenlandicum (Labrador tea). Leaves are very hairy which gives the plant an unusual effect in the landscape. Heat and cold tolerant but the sun tolerance is untested. It can take one-half of a day of sun here with no trouble. Easy to grow and problem free. A rare plant in cultivation but should be used more. Plant habit is rather informal. Don Paden possesses a large leaved variety of this plant that has to be seen to be believed. Flowers are white.
Ledum palustre. Native to northern Asia. Plant habit is much tighter than L. groenlandicum. The flowers stay in bloom much longer and is a more prolific bloomer. Outstanding foliage plant. Everybody should have one. A trouble-free plant.
Kalmia latifolia (Mountain laurel). Cold tolerant. Outstanding foliage plant but all forms are slow growers. Many forms available. Late bloomer. Does not tolerate direct sunlight well here. Everybody should have at least one.
Pieris phillyreifolia. In its native habit, north Florida, south Georgia and south Alabama, it usually has a vine-like growth habit. It is especially fond of bald-cypress trees. If restricted to its own roots it is a dwarf shrub. Surprisingly cold tolerant but it needs some winter protection. A rare plant in cultivation.
As even the casual reader of this article can see some of the plants mentioned here are not readily available in the local market place. Therefore, I would recommend the nurseries listed below as possible sources.
Greer Gardens, Eugene, OR
The Bovees Nursery, Portland, OR
Siskiyou Rare Plant Nursery, Medford, OR
The Cummins Garden, Marlboro, NJ
Woodlanders, Inc., Aiken, SC
Daystar, Litchfield, ME
If this article has stimulated any curiosity about possibly growing any of these plants a word of warning is in order. Many of these plants are native to areas that have very infertile soil. Therefore nitrogen fertilizer can not be used under any circumstances.
The reader should keep in mind that the author probably has a tremendous advantage over most readers and it is the soil. In my yard the soil is a black sand that has a reasonably high organic content, just about an ideal situation for ericaceous plants. Therefore the drainage is always excellent; I can't ever recall seeing water standing anyplace in my yard for even five minutes.
I maintain a pH of 4 in my flower beds by adding ferrous sulphate twice a year, once in the Spring and once in the Fall. In the Spring I also add superphosphate because it seems to help the plants through the Summer. Phosphate also increases flower bud formation.
I am also a great believer in gypsum, which I add during the summer. Ericaceous plants seem to have a healthy appetite for non-basic calcium. Gypsum seems to improve flower color also.