JARS v46n2 - Ericaceous Companion Plants

Ericaceous Companion Plants
Arthur P. Dome
Seattle, Washington
Article based on an illustrated seminar presented at the 11th Annual ARS Western Regional Conference, Olympia, Washington, October 6, 1991

Rhododendrons are ericaceous plants so it is only natural to use other members of the family as companion plants. In addition to species of the Erica and Calluna genera, which are the most widely used, there are many other interesting, desirable and usable plants for us in the Pacific Northwest to consider.
The main thing to consider in keeping these plants happy, as with all plants, is to plant them in the correct situation with proper soil, moisture and light. Generally they do best in a light, lime-free, well drained soil that never dries out, and they should have adequate moisture during the growing season. They like to be out in the open, but most species cannot tolerate the direct, hot afternoon sun especially if it causes the soil to get too hot. Some can, however, tolerate the heat and a few seem to like it, once established for a year or more. The blooming period of the different genera discussed here ranges from spring to early summer, and some will produce varying colored fruit later in the year.
Some of these shrubs can be used as border plants in front of larger rhododendrons or as background plants for some of the lower growing types. Others can earn a place in your garden because they're so floriferous that they can really enhance any size of planting. Some, such as the enkianthus and vacciniums, have forms that develop very fine fall color. Then there are those that are very useful as ground covers, and some of the dwarf species can really make a trough more interesting.
The Andromeda genus is a group of small shrubs that usually like a more moist soil than the other plants we'll be talking about. They should not be allowed to bake in the hot afternoon sun. Different species can grow from 6 to 18 inches tall. Andromeda glaucophylla has glaucous colored foliage and pink blossoms, A. polifolia macrophylla has broader foliage and pink blossoms, A. polifolia 'Kiri-Kamig' form has very narrow leaves and pink blossoms while the A. polifolia alba has typical foliage and white blossoms.
Members of the Arbutus genus can get quite tall and once established can tolerate the hot afternoon sun and a drier soil. Our native Arbutus menziesii is a good example. Arbutus unedo is used more than any other in our garden. It can grow to about 12 feet tall. There is a compact form for those who want a slower growing plant. It has cream colored blossoms and bright orange to red fruit in the fall.

Arcterica nana is a tiny little plant that might get 4 inches high. Some forms are very floriferous with cream colored pieris-like blossoms. They must be protected from the hot afternoon sun.
The genus Arctostaphylos does well in the hot afternoon sun, also once established. The kinnikinnick ( Arctostaphylos uva-ursi ) is very popular as a ground cover, and there are several named selections. It can grow from 6 to 10 inches tall, has pink blossoms and red fruit later on in the year. A. x media forms a shrub about 2 to 3 feet tall and has pink blossoms.
The Cassiope genus on the other hand does best in the open but must be protected from the hot afternoon sun. In our mountains they are known as the "white mountain heather." All cassiopes have white flowers. Cassiope x 'Badenock' is a hybrid that gets about 6 inches tall, C. fastigiata is more upright reaching about 9 inches tall, C. tetragona gets up in the 12 to 18 inch range depending how it is grown and C. lycopodioides is usually prostrate about 2 inches tall with the 'Beatrice Lilley' form being more compact and about 4 inches high.
Daboecia is a very floriferous genus. The Daboecia azorica blooms in April and May, gets about 8 inches tall and has deep crimson blossoms. Daboecia cantabrica can bloom into the late fall and has forms that can grow 24 inches tall. There are white, pink, rose and purple blooming forms. The daboecia can bloom well with about one-third the need for direct sunlight.
The Enkianthus genus is very interesting with its pendant, bell-shaped blossoms that always attract attention. Some of these plants can get up to 10-12 feet tall, and the fall color of the foliage can be outstanding. Different forms of Enkianthus campanulatus have blossoms of white to red, E. cernuus rubens is a very fine deep red blooming species while E. perulatus has interesting white blossoms.

The gaultherias are a superb group. Some of them spread by underground rhizomes which make them ideal for ground covers. They do well in the shade, but they will bloom better and produce more fruit with the more light they can get. Gaultheria adenothrix is a super plant with dark green foliage, grows about 12 inches tall and has white blossoms a little larger than most and red fruit. Gaultheria cuneata has shiny green foliage with white blossoms and white fruit; C. itoana has small, narrow leaves, grows 6 to 8 inches tall and has white blossoms and white fruit; G. miqueliana is very similar to G. cuneata ; G. nummulariodes nana is a prostrate form growing about 1 inch tall with pinkish blossoms and black fruit; G. procumbens is our native wintergreen growing 3 to 6 inches tall with white blossoms and red fruit; G. shallon is our native salal growing 2 to 6 feet tall with white to pinkish blossoms and dark purple fruit.

Kalmia latifoiia is a very fascinating species with its individual saucer-shaped blossoms producing a kaleidoscope of patterns in varying shades of pink, red and rose. Most of them can tolerate a warmer, more open location. Some of these plants can get 6 to 10 feet tall. Kalmia polifolia is also one of our native kalmias found mostly in wet areas, growing from 1 to 2 feet tall with saucer shaped pinkish-purple blossoms.
The Kalmiopsis leachiana is endemic to certain parts of Oregon and can be quite showy in our garden. It usually grows out in the open up in the mountains, but in my garden it does better if it is protected from the hot afternoon sun. These plants usually grow from about 8 to 12 inches tall with rich pinkish blossoms. There are two forms, the 'Umpqua' form and the 'Curry County' form. There is also a hybrid between the two made by Peter Cox of Scotland named 'Glendoick'.
Ledum glandulosum is a West Coast native that is not used too often in our gardens. It can tolerate the hot sun if the roots are kept moist. It is an upright growing plant that can get 3 to 5 feet tall. Its white blossoms form a truss about 3 inches across.
The Leucothoe davisiae also is not seen too often in our gardens. It has white blossoms similar to the pieris, but the foliage is usually a brighter green. It is an up-right growing plant that can reach between 2 or 3 feet tall.
Loiseleuria procumbens is a little, compact, slow growing plant that won't get much taller than 2 to 3 inches. Better forms can be covered with numerous tiny pink blossoms. Protect it from the hot afternoon sun.
Menziesia ciliicalyx is a deciduous shrub. Its bristly new growth is very interesting. It grows 2 to 3 feet high and the blossoms can vary in color from pink to reddish-purple. The variety M. ciliicalyx purpurea has deeper colored blossoms.

Pernettyas are a fine group for a sunny location, once established, as they do not need the amount of moisture that the rest of these plant do. Pernettya mucronata is the species mostly grown in our area, reaching up to 5 to 6 feet tall, and has white blossoms. Happy, mature plants can be covered with white or pink to deep purple fruit in the late summer and fall depending upon the species. Pernettya pumila grows about 4 inches tall with white blossoms. My plants have never set fruit. Pernettya empetrifolia is similar to the P. pumila but has larger leaves and grows to about 6 inches tall. It has produced white fruit in my garden.
Phylliopsis is one of the group of intergeneric hybrids ( Kalmiopsis leachiana x Phyllodoce breweri ). There are two of them: P. x 'Copelia' and P. x hillieri 'Pinnochio', both growing between 9 and 12 inches high. The foliage of the 'Copelia' resembles that of the phyllodoce more than the 'Pinnochio' does. They both have rich pink blossoms. Again, protect them from the hot afternoon sun.
Phyllothamnus erectus is another intergeneric hybrid ( Phyllodoce empetriformis x Rhodothamnus chamaecistus ). It is a nice little plant that can grow up to about 12 inches tall, has pinkish blossoms and must be protected from the hot afternoon sun.
The genus Phyllodoce is very desireable group of plants. Our mountain heath, Phyllodoce empetriformis is familiar to all of us. With the phyllodoce one can have a selection of white, yellow and most shades of pink to rose colored blossoms depending upon the species. In our gardens different species usually grow from 4 to 12 inches high, and I have seen P. empetriformis about 24 inches high in the mountains. They also must be protected from the hot afternoon sun. Phyllodoce aleutica grows about 8 inches tall and has yellow to greenish-yellow blossoms; P. breweri can get up to 12 inches tall and has very interesting pink saucer-shaped blossoms; P. caerulea grows to about 8 to 10 inches tall and has lavender-pink blossoms that seem to turn darker as they get older; P. empetriformis usually gets about 12 inches tall in our gardens and has pink to rose colored blossoms; P. glanduliflora has yellow flowers and seems to be an easier plant to grow in our gardens than P. aleutica and can grow 10 to 12 inches tall; P. nipponoica is a real little jewel from Japan growing 8 to 10 inches and has white blossoms; P. x 'Flora Slack' is a hybrid growing to about 8 inches with pale white urn shaped blossoms; P. x 'Fred Stoker' is another hybrid growing to about 10 inches with pinkish-lavender blossoms.
Pieris is a variable genus with dwarf forms as well as those that can get quite tall. The larger growing forms can do quite well in the open but the color of the foliage is not as deep a green. I find the dwarf forms do better if they can be protected from the hot afternoon sun. Pieris formosa var. forestii is a spectacular one with its salmon to flame colored new growth. Pieris japonica is an upright growing shrub that can get up to 10 feet tall and produces numerous drooping racemes of white blossoms. Pieris japonica 'Bisbee Dwarf' is a compact, slow growing plant that gets to about 12 to 15 inches tall. Its new growth is an orangish-red and its blossoms are white. Pieris japonica pygmaea has small, very narrow leaves and may get 12 inches tall and has drooping clusters of white blossoms.
Rhodothamnus chamaecistus is another nice little slow growing plant that is very difficult to grow. It can get as high as 12 inches, has pink saucer-shaped blossoms and should be kept out of the hot afternoon sun.
The genus Vaccinium is a very useful group of plants with some prostrate forms to some that can get 7-8 feet tall. Some of the deciduous species can have very fine fall foliage color. The prostrate and dwarf forms are the most popular. Many of these plants can spread by underground rhizomes, which enhances their desirability as ground covers. They can tolerate quite a bit of sunlight if the soil can be kept moist. In this situation you can get more blossoms and fruit, but the color of the foliage will be poor. Vaccinium crassifolium 'Well's Delight' is a fine selection from the North Carolina State University. It has good foliage and grows to about 8 inches tall. The blossoms vary from white to pink, and it has dark purple fruit. Vaccinium macrocarpon 'Hamilton' is a real dwarf shrublet that has very dark green foliage. It may get about 4 inches high and has rosy-pink blossoms and red fruit. Vaccinium moupinense grows to about 12 inches tall and has mahogany-red blossoms. It is supposed to have purple-black fruit but mine has never set any. Vaccinium nummularia is a very interesting plant with small, round shiny leaves with the stems covered with fine bristles. It can get 12 to 18 inches tall and has numerous pinkish colored blossoms. In the winter '90-'91 mine was cut to the ground, but it is coming back from the roots. Vaccinium ovatum is our native evergreen huckleberry in the Pacific Northwest that can get up to 3 to 5 feet tall, but a pair of pruners can keep it where you want it. It has white to pinkish blossoms and deep purple fruit. Vaccinium vitis-idaea grows 6 to 12 inches tall and develops into an ideal ground cover. It has white to pinkish colored blossoms and can produce numerous bright red fruits. Vaccinium vitis-idaea minor is a slower growing, dwarf form that rarely gets over 3 to 4 inches high.

Art Dome has been a member of the ARS since 1952. He is a past ARS director and past president of the Seattle Chapter, He is currently a director of the Rhododendron Species Foundation and serves as judge at rhododendron shows. He enjoys photographing flowers and plants wherever he travels.