By Rex D. Pearce, Hendersonville, N.C.
The genus Rhododendron is simply one among the many genera belonging in what is often termed the "Heath" family, or, more technically, the Ericaceae. With just a few doubtful and minor exceptions, the members of this group have woody, persistent stems, and may be classed as shrubs or near-shrubs, save for the few that are of a height and habit that brings them into the class of trees. Most of the members of this interesting group have evergreen foliage; nearly all of them have attractive flowers.
In general, they quite differently prefer acid soil, although some, as Calluna, have a considerable tolerance range in this respect. Many of them have values for horticultural effects that approach, or equal, those of the genus Rhododendron. Others, with smaller, less spectacular flowers, are desirable for under planting, or even as ground covers. Since all of these plants are akin to rhododendron, with roughly the same needs as to soil, exposure, climate and light, these other members of the Ericaceae mostly fit well into any planting scheme with rhododendrons. Many of them have a general likeness to rhododendron in foliage effects; some few of them also in flower form and coloring.
Now it is possible to classify any group of plants in many different ways, depending upon the base or standard that is used. The taxonomist classifies upon a basis of differing or like morphological characters, which is just another way of saying that he works by making comparisons of points of structure and form in the various plants he has under study. The gardener, or landscape planner, more often thinks first of the average height of the plant, since the eventual height is an important factor in deciding where and how the plant should be used, but he must also consider time of bloom, color of flower, adjustability to varying amounts of light and shade, adaptability to his particular soil and drainage conditions, and the like. But one cannot classify plants on half a dozen different bases at once, without confusing even confusion-any more than one can slice a cake in several different directions, and at varying angles and have very much left that is usable, so I shall make only the roughest attempt to present the different kinds in a classified order, following simply an approximate, and sometimes inconsistent, plan of going from the lower kinds to the taller ones. Then as each kind comes up in the story, I shall try to mention the more important characteristics so far as needs, culture, adaptability and planting values are concerned.
I am sorry that I cannot illustrate as I talk, but I do not have slides available, and there would seem small point to bringing in of specimens of the foliage, when, as now, the flowers are out of season. I realize that you will not remember too much of what I give by simply word description, without visual image to help fix the appearance of the kinds in memory, but I shall be happy if I can just bring the realization that the genus Rhododendron does not stand alone, that there are very many other genera, species and cultivars in the same general family group that may well be brought into our gardens along with, and beside, the Rhododendrons and Azaleas. The greater the range of plant materials that we know, the more plastic and expressive will our gardens become.
Since we are considering the general "Heath" family, perhaps our first subgroup should be the plants that are commonly called the Heaths and the Heathers. To many, the word Heather seems the broader term, used by them to include the Heaths also, much as many visitors to our North Carolina mountains, may call the whole complex of ranges and ridges, the "Great Smokies" or again, the "Blue Ridge," but actually Heath and Heather are not interchangeable terms. More precisely, a Heather, is a variety, (cultivar), of the genus Calluna, only. In Calluna the tiny leaves are scale-like, and appressed, or laid closely against the stems, bearing some resemblance in miniature to the leaves of Thuja, the arbor-vitae. There is but one genus of Heather, just Calluna, but there are a rather large number of horticultural varieties, or cultivars, of this genus. There cultivars differ amazingly in appearance. Some make a fine, moss-like, deep green growth to not more than two inches of height. Others may be diffusely branched, or of erect habit, reaching a height of three feet or more. Foliage coloring may be anything from palest green, to rich, dark emerald, and there are forms with foliage that is close to yellow, or again with tones of bronze or purple. Other kinds may be green in summer, but golden, coppery or maroon in winter. Many, though, are one uniform green year through. The flowers are campanulate, individually small, but produced over a long season in early summer in an effective, and almost unbelievable, profusion. Blossoms may be single, or double; colorings running from pink, lilac or rosy red, to purple or pure white. The wild heather of northern Europe shows mostly blossoms of rosy violet, near to purple. The Callunas will grow in full sun, or they will tolerate some thin shade. They like good drainage, and are supposed to prefer light soils, but I find that they also do very well on the red clays common to the Carolina mountains. The smaller kinds of Heather fit the rock garden, or they may be used as edgings, or for cover on bank or terrace. The taller kinds are effective toward the front of mixed shrub plantings, including those of, or with, Azaleas and Rhododendrons, but if positioned too far back among taller woody plants, there is some danger that the relatively slow Heathers may, in time, be overgrown. Calluna ranges through northern and central Europe, and into western Asia, particularly into the higher central plateau of Asia Minor. The typical, or wild form, is often called Scottish Heather, but with equal reason it might be called German, Swedish, Polish, or even Turkish Heather, for it is indigenous to all these countries, and to others.
The true Heaths, in the limited, precise use of the name, all belong to the genus Erica (from which the wider term Ericaceae comes). In Calluna (Heather), we had but one genus, and but one species, with many cultivars. In Erica (Heath), we have, in contrast, around 500 botanic species in the single genus, and additionally, a liberal bonus of horticultural varieties (cultivars). Further, while the range of Calluna as it grows naturally, is pretty much in contiguous territory (save as it has naturalized in limited areas of North America, South America and New Zealand), the range of the true Heaths, or Ericas, includes not only the territories occupied by Calluna, but also Africa clear to the Cape of Good Hope, beside a wider extension into Asia. In Erica the leaves differ from those of Calluna in that they are tiny spikelets, usually carried at close to right angles with the stems.
Most of the Heaths are summer blooming, but Ericas carnea and mediterraneana flower in winter, displaying pretty pink bells from early January, through April. Even if the plants of these two are covered with snow, all one need do to see their early edition of spring-in-bloom is to shake the snow away. Incidentally, a rather satisfactory hybrid of Ericas carnea and mediterraneana is sometimes offered as Erica x Darleyensis. It is, perhaps, slightly to be preferred for garden planting over either of its parents. Several Erica species may be considered as reasonably winter-hardy in the Carolina mountains. These include Ericas carnea vagans, (Cornish Heath), cinerea (Gray Heath or Bell Heath), tetralix (Cross Heath), mediterraneana (Mediterranean Heath); lusitanica (Portuguese Heath) and stricta (Corsican Heath). The three latter are the taller growers. Erica stricta is slightly less winter-resistant than the others, and should be given a sheltered position. The African Heaths, and particularly the large number of Erica species that are found in the Cape of Good Hope region, are all rather tender. They are sometimes grown in pots, under glass, in the north. In California several of the species are used for commercial cut flower production in the open. The flowers of this Heath group are particularly beautiful.
Getting back to the winter-hardy Heaths, the needs, uses and heights are about as in Calluna, except that Ericas stricta and mediterraneana may eventually reach four feet, and E. lusitanica to ten feet. These taller species may, with discretion in placing, be inter-planted with azaleas and rhododendrons. There is at least one Heath, too tender for our climate, that be comes a full-fledged tree, to fifty feet, forming true forests on the upper slopes of the Ruwenzori massif in Uganda, and above the 10,000 foot line on Mt. Elgon, in Kenya. It is Erica arborea.
Two of the plants that are quite usually known as Heaths, belong to other genera than Erica. The so-called Irish Heath is Daboecia cantabrica, and by human relationship standards it would certainly seem to be at least a first cousin of the true Heaths. It is a beautiful plant, with many graceful branchings set thickly with grass green needles, that are, however, soft to the touch. The flower-bells are rather larger than in other Heaths, typically of a violet-hinting rose. There is a white-flowered form, too, this of a particular loveliness. Daboecia may show winter-burn, or even partial killing, if exposed to winter winds, but given a sheltered position, it does very well here.
The other near-Heath that belongs to a genus distinct from Erica, is Bruckenthalia spiculifolia, the Spike-Heath. It is a delightful plant, growing to twelve inches, the closely packed, soft leaf-needles giving the effect of green fur. In summer it blooms freely, filled with dainty little flower-bells in deep pink. It has not winter-killed with me at any time, either in Philadelphia, or here in the Carolina mountains.
As to propagation, all of the Heaths and Heathers, including Daboecia and Bruckenthalia, strike well from summer cuttings. The species may also be grown from winter-sown seeds.
One of the prettier members of the Ericaceae is the Trailing Arbutus, Epigeae repens. It grows here and there through eastern America, and although it is far from being a common plant, and certainly not a common-place plant, I think about everyone has seen it, and knows it. Perhaps because of its rather scanty root system, it resents moving, being difficult to transplant unless handled when very small. With care, though, it is possible to grow it from seed, and a few growers claim to be able to successfully strike it from cuttings. In our area it is a plant of thin woodlands. Further north it grows also among low bushes and scrub-oak in the three American areas that are said to closely resemble the open heath-lands of northern Europe, being the central part of Nantucket Island, and the two odd, elevated expanses in Atlantic County, New Jersey, that are known as the Upper Plains and the Lower Plains. There are but two species of Epigeae, the other, Epigeae asiatica, being native to Japan.
Among other American members of the Ericaceae are two fully hardy, low trailers with pretty, but tiny, flowers, and bright red fruits. Both are valued as ground covers. One of them, Arctostaphylos uva-ursi, is notable first of all, for the oddity of its name. The genus name, Arctostaphylos, comes from the Latin, and translates literally as Bear-berry; the species name uva-ursi, comes from the Greek, and may also be translated as Bear-berry. Then we have the English common name, which is, quite naturally, also Bearberry. Anyway, the Bearberry makes an excellent ground cover for light shade and on light soils. The tiny, pink hinting flowers are followed by brilliant, red berries. The foliage is evergreen. Although I have called it American, the Bearberry is native also to Europe and to Asia, being one of the comparatively few plants with a circumpolar distribution in the wild. Two other circumpolar plants are Lily of the Valley (not of the Ericaceae), and the loiseleuria or Creeping Azalea. To the American Indian, Bearberry was one of the kinnikinnics, meaning only that it was one of the plants that they used for smoking. Another favorite Indian kinnikinnic was made of the dried young leaves of the willow. The other low, America, ground-cover plant referred to above, is Gaultheria procumbens, the Tea-berry, known also as Checker-berry and as Wintergreen. It has little, waxy white flowers, followed by red berries of true wintergreen flavor. However the wintergreen oil of commerce comes from one of the Birch-trees, Bbetula lenta. Both Arctostaphylos and Gaultheria may be grown from seeds sown out of doors in winter; also from summer cuttings. Before we leave Gaultheria, it might be mentioned that there are several other species of it that are desirable for landscape use, as the little Gaultheria trichophylla of the Himalayas, pretty in rock gardens, the taller, blue berried Gaultheria veitchiana of western China, the five-foot Gaultheria antipoda of New Zealand and Tasmania, beside the two or three good, shrubby Gaultheria species of our own west coast.
A pretty little Ericaceous shrub-let, native to our own Carolina mountain tops, as on Roan Mountain, but coming down into the coastal plain further north, is the Box Myrtle, Leiophyllum buxifolium, with dense branchings filled with little evergreen leaves. The flowers are individually small, but so many that they hide the foliage. Through May each plant is a mass of pink-flushed white blossoming in rather a fluffy effect. It varies in height, low, almost prostrate, in the mountains, but reaching 20 inches in the coastal plain. It is a good rock garden plant, or for use among azaleas. The low-land form is more adaptable, and more easily propagated than is the prostrate form of the higher mountains. It may be grown from summer cuttings, or from winter seed-sowings.
A low shrub that is rather close to the Azalea section of the genus Rhododendron is the 'Creeping Azalea', Loseleuria procumbens. It has a circumpolar range, at sea-level far north, but climbing to high mountain altitudes toward the southern edge of its range. The growth is low, tufted, semi-creeping; the flowers pink, rather like little azalea blossoms. It is a desirable plant for cool, north-facing rock gardens, and it may be grown from the seeds, which are, however, only occasionally available. Close to Loiseleuria, and to Rhododendron, is the little Rose-shrub, Rhodothamnus chamaecistus. It is a mountain plant, evergreen, rarely going above 9 inches of height. The charming pink flowers remind of those of Kalmia. Try it in peaty soils, among rocks, exposure northern.
The Kalmia reference recalls another low shrub, an even rarer one, Kalmiopsis leacheana, in other words, the "shrub that looks like Kalmia, and so far as blossom effect goes, it assuredly does resemble Kalmia. It is an American plant, native to Oregon, but found there at only a few isolated stations. It is an evergreen, height about 10 inches, the plants spreading slowly by underground runners. The handsome blossoms come in a rich pink. It is of a considerable winter-hardiness. Preferred situation for it would be at an altitude of 2000 feet or above, in well-drained soil. Always it prefers drought to wet feet.
Of the true Kalmias, it is Kalmia latifolia that is by all odds the most important species from the horticultural angle. It is K. latifolia that is known in most areas as 'Laurel' or as Mountain Laurel. The local name among our own mountain-folk is Ivy, but up in the mountains of Pennsylvania it is called Honey-suckle. Here is a good demonstration of the need for use of scientific names as a matter of precision. Kalmia latifolia, at least in the forms with deep pink flowers, is one of the more beautiful of American evergreen shrubs, worthy of far wider use and attention than it now receives. There are several other, lower, Kalmia species, the best being Kalmia angustifolia, with rosy crimson flowers. The Kalmias grow well from seed.
A good shrub for wet, poorly drained places is Chamaedaphne calycalata. It can be rather effective when grown in masses, showing great quantities of little, pure white flowers. I hope that I shall not give you an unpleasant association-reflex for this plant when I mention that the common name for it in at least the northern part of its range, is False-teeth Bush, from the even racemes of pearly white flowers. Chamaedaphne is evergreen, will eventually reach three feet, and will even grow and bloom in places where water stands over the roots part of the season.
Among the taller shrubs in the Ericaceae, my choice for first beauty, after rhododendron of course, would waver between Enkianthus and Pieris. Of the Enkianthus species, E. campanulatus is the easiest to come by, and if perhaps E. cernuus may equal it in ornamental value, I am quite certain it cannot surpass it. The flowers of Enkianthus campanulatus are carried as clusters of little bells, yellow to pale orange, striped and veined red. It is deciduous, but the leaves turn deep red before they fall. Enkianthus campanulatus grows to ten or fifteen feet, or sometimes even higher. In our area it is safely winter-hardy. Usually it is grown from seed.
In Pieris, as with Shortia, Epigeae and many other genera, there seems to have been two main, and balancing, centers of dispersal, one in southeastern North America, the other in southeastern Asia. The Pieris species most widely planted, P. japonica, is marked by its name as being of the orient. It becomes a tall shrub of particular grace and elegance of form, the evergreen foliage bronze-toned in winter. In spring it carries a wealth of white blossoming in drooping panicles. Another Pieris of equal worth for planting use, an American species this time, is Pieris floribunda. Compared with P. japonica, it is not quite as tall, and the great panicles of handsome white blossoms are carried erect, rather than nodding. The foliage is evergreen, the blooming season early, and it may be considered a fully hardy and adaptable species. These two Pierises will fit very well into any planned scheme of Rhododendron planting. There are several other good Pieris species. One that is a particular favorite of my own is Pieris mariana. Unlike the others, P. mariana is fully deciduous, the clustered flowers appearing in early spring before the leaves. The blossoms are larger than in the other Pieris species, the petals thick and crispy as though cast from wax. The flowers are white, with just a hint of pink suffusion. All the Pierises grow well from seed; also from summer greenwood cuttings.
Now there are a lot of other good Ericaceous plants that have their place in landscape planting. If you want a hardy tree, there is Sourwood, Oxydendrum arboreum, famed for its honey, with little white flowers carried in gracefully spreading, plumelike panicles, attractive both in bloom and in seed. The deciduous foliage becomes a burning scarlet before it falls.
Then there is Leucothoe catesbaei, an evergreen shrub to six feet, with racemes of pretty white flowers. The foliage is so attractive that it is cut for commercial use in the florist trade. A splendid shrub of all-round decorative value, it is desirable for massing or foil use in planting planning. Although other Leucothoe species are good, too, L. catesbaei is perhaps the best of the group.
Circumpolar distribution does not always mean about the north pole, for at the other end of the earth we find the Pernettyas in their several species, in southern Argentina and Chile, and again in New Zealand and Tasmania. Perhaps the easiest of them, and fortunately also the best of them, is Pernettya mucronata, from lower Patagonia to the Straits of Magellan, and beyond, into Tierra de Fuego. It's an evergreen Heath-cousin, with shining prickle-tipped leaves, and, in summer, longhanging, beautifully colored berries that may be pink, red, crimson, lilac, violet or white. Pernettya is a shrub of truly first-rank quality, in the 25 to 35 inch height range. Plant it with heather, with azaleas, or near the lower rhododendrons. As with the hollies, the sexes are separated, the plants male or female, and this must be taken into consideration if you expect a display of the showy berries. When the plants are grown from seed, you will, of course, have a proportion of each sex. Any particularly desirable clone may be propagated vegetatively, by layering.
For the specialist there are several delightful, smaller members of the Ericaceae, plants for the cool rock garden. All are highly desirable, but also all, with one possible exception, are rather hard to grow. They include the several species of Cassiope and of Phyllodoce. One species of the latter, Phyllodoce empetriformis, might be attempted. It is a dwarf, (to 6 inches), heather-like plant with glossy green foliage, and clusters of beautiful, deep pink bells at the ends of the stems. It is of fullest winter-hardiness, and, in general, it is less exacting in its requirements than are the other Phyllodoces and Cassiopes.
Native to the piedmont and upper coastal plain of the American southeast are three reasonably hardy, and rather good shrubs as yet rarely seen in gardens or in landscape plantings. Of the three, Elliottia racemosa is perhaps the most sought after not because it is the horticulturally best of them, but rather because it is the rarest, both in the wild and in nurseries. It is deciduous, white-flowered, and will, where it is happy, reach a height of 15 feet in time. It increases by stolons. Elliottia is well worth planting, but it is hard to get, being a far rarer plant than the Shortia galacifolia of which so much is made. At one time, all wild stands were supposed to have disappeared, but it is now believed that there are stations for it still known to a few. The second of these less-known southeastern shrubs is Zenobia pulverulenta, deciduous or semi-deciduous, with handsome racemes of fragrant white flowers, these coming before the new leaves appear. The foliage is a powdery, glaucous blue-gray. Zenobia will reach about four feet. The third of the southeastern shrubs, Befaria racemosa, is evergreen, and reaches six feet. It is a showy long-bloomer, with quite large white flowers that hint of pink.
I should not close without at least mentioning Vaccinium, and Gaylussiaca. The latter is the huckleberry. Vaccinium covers, among its many species, the true Blueberries, the Cranberries, the Sparkle-berry, the Dangle-berry, and the European Whortle-berry. Prime consideration of the horticulturist with these two genera has been with, and because of, their mostly cinium covers, among its many species, have some ornamental value, and the High-bush Blueberry, Vaccinium corymbosum, is definitely well worthy of ornamental planting use.
Now there are many other genera and species in the great Heath family, to which rhododendron belongs, but there is neither room nor time to consider them here. I do want to mention, though, Ledum, Lyonia and Andromeda, all good landscape shrubs. One of the Ledums, by the way, is called Labrador Tea because the leaves of it are supposed to have been one of the substitutes used for tea by the colonists during the American Revolution. Despite the "Labrador" part of its common name, Ledum groenlandicum ranges, in the wild, as far south as Pennsylvania.