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Journal American Rhododendron Society

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Dr. Glen Jamieson ars.editor@gmail.com


Volume 7, Number 3
July 1953

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Native Azaleas in Naturalistic Plantings
By Edward L. Manigault

        The average amateur gardener, especially if he is building a new home, is often puzzled when he considers the type of planting he should follow. A landscape architect, or an expert gardener with many years of experience, could make the proper analysis in short order.
        They know that the answer to the sixty-four-dollar question-"Shall it be formal or informal?"--primarily depends upon the type and scope of the property to be developed. The financial status of the owner, the procurability of plant material, the availability of maintenance labor (if required) and, to some extent, the geographical location are several of the other factors that are germane.
        Unfortunately, however, not all of us are so situated that we can obtain the services of a landscape architect. And there are not too many experienced gardeners from whom we can absorb valuable information at just the time we might need advice. Therefore, a garden encyclopedia plus a few carefully-selected magazines that deal with various aspects of gardening are highly desirable for most of us. From these, we can fairly well determine for ourselves the main facts to guide us in planning our garden not only for the immediate future but also for the many years ahead. We will make some mistakes, but they won't be too hard to rectify.
        Because formal gardens are generally the more difficult to plan, and often the more expensive to maintain, most people favor the informal type-often termed, "the naturalistic planting." It is this type which we wish to discuss, giving particular emphasis to what many consider to be America's most valuable decorative shrub-the native azalea.
        Offering infinite variety of color and a wide range of inflorescence, our wild azalea can be so perfectly blended with other ericaceous plants that it will appear as though Nature had done the work. This is its true role; and thus is it best glorified. And yet it is also possible to make mass plantings of azaleas in similar and supplementary colors without destroying the naturalistic scheme. We find such masses, or stands, in the woods generally in clearings subjected to full sunshine. While such groups in full bloom areas gorgeous as a huge bouquet, they nevertheless do not express the stiff formality of the mass planting in a meticulously-kept bed set off by itself. The reason is obvious. In the woods or old fields, there is the natural blending effect that cannot be had in the formal bed that is groomed to perfection. Breath-taking effects can be created by formal masses of native azaleas; however, they loss a great deal of their natural charm unless they are given a proper setting with background or companion planting. A tapering effect (if only a few ferns) in the edging, is much desired. Thus we see the versatility of our azaleas when they are employed in naturalistic arrangement.
        While there are twenty azaleas native to North America, only nine will definitely thrive in the colder regions. However, three additional species, of limited range, may later be proven satisfactory for such areas. Care must be exercised, therefore, in the selection of any species which we may wish to use in addition to those native to our particular region. At the end of this article, the azaleas are classified according to use in the various climatic zones. (Charts 1 and 2).
        The most satisfactory and successful basic plantings are made with the flora, endemic to a particular region. Sometimes, however, we can supplement with several reliable plants from other areas, or even from foreign countries, if we are sufficiently experienced. Other than a few exotics of long standing on the nursery list, we will discuss only the native stock, particularly that indigenous to the Appalachian Area.
        The main problem for the amateur is the proper grouping of azaleas according to color and time of bloom. (See Chart 1 or 2, according to your area). The early bloomers of Chart 1, for instance, are of the pink-orchid-lavender group. Certain of these sometimes overlap a few individual plants of A. calendulacea, a species in which yellow and orange predominate. Although a clear, pale yellow can be skillfully blended with a pink color scheme, still it is safer to plant the early-flowering species some distance from the yellows.
        The early varieties blend delicately with pink dogwood and with many other flowering trees-crab, cherry, etc., available from nurserymen. Beautiful contrast is offered by a white background of the shadbush and the native dogwood, which bloom in succession and thus last thru the entire group of pink azaleas. Many varieties of dogwood, including dwarf forms, are in commercial cultivation. Both the white form of the Judas tree Circis canadensis alba and the wild magenta form, familiarly called redbud, occasionally bloom with some of the very early azaleas.
        The azaleas should be planted far enough from the background trees to prevent branches from interfering in later years. Dogwoods are generally low-branched. If branches of deciduous trees are high we can base-plant, where desirable, either with azaleas or with small evergreens and other low-growing material that will thrive in partial shade. A heavy effect is not advisable in all locations, however. Native hemlocks Tsuga canadensis and T. caroliniana can be pruned to grow horizontally, but should be limited to a spread of about three or four feet in locations subjected to heavy snows. Otherwise, the upper branches are apt to break off at the main stem. If we start with small plants, almost any effect can be created by pruning. Certain of the smaller yews, such as Taxus cuspidate nana, T. cuspidate dense, T. canadensis stricta, etc., and the various prostrate types of juniper, like Juniperus horizontalis, J. communis var. depressa, etc., are excellent and are generally in nursery stock. There are many species and varieties of dwarf evergreens from which to select. The local nurseryman can assist you by suggesting those best suited to your region.
        Broad-leaved evergreens, such as the rhododendron and the mountain laurel, can be inter-planted in many ways with the flowering trees, the coniferous evergreens and the azaleas. Thus, even in late summer, after the flowers have disappeared, we can enjoy not only the varied patterns of sunshine and shadow but also the contrasts afforded by the many shades of green and the several types of foliage.
        The majority of the broad-leaved evergreens do best in locations subjected to considerable shade for a part of the day or to very light shade continuously. Dense deciduous trees of ornamental types, and others such as cherry, buckeye, sourwood, beech, certain oaks, etc., can be suitably planted among unprotected rhododendrons, for instance. White ash is superb. Lower branches of such trees must be removed to sufficient height, as the evergreens grow, to admit full sunshine for a portion of the day. Upper branches can be thinned out for additional light. Loosely-branched trees with light foliage-plum, redbud, dogwood (generally), shadbush, sassafras, mountain ash, birch and many others-need practically no pruning, except to keep lower branches out of the way. Their light shade is ideal.
        For best results, do not plant near rhododendrons and azaleas any surface-feeding trees like elms and maples; and stoloniferous types like silver poplar, sumac, ailanthus or Hercules club; or any "drippers", like the lindens, tulip tree or Norway maple that drop honey dew copiously.
        Tall conifers located to the west can be very effective in the winter in shielding the broad-leaved evergreens from the evening sun. In this mixed planting we can readily gain the effects so necessary to informality-the wavy or irregular border and the ever-changing view that keeps beckoning as we walk along. Here is a shallow border that catches the eye for only a brief moment. Then a mass planting that holds the attention while the mind registers its varied degrees of appreciation. Around the curve, we come suddenly upon a group of bright azaleas. They fill a small cove formed by a background of towering rhododendrons and a slow sweep of two species of kalmia that taper toward a long vista. The dense plantings often serve to separate clashing colors of some of the larger azaleas.
        The various species of native rhododendron do not all bloom at the same time-see Charts 1 & 2. Therefore, they should be properly grouped to obviate color conflict with certain late azaleas of Chart 1 and the brilliant hues of Chart 2. This is especially important with respect to Rhododendron catawbiense and R. minus. A popular use of the larger rhododendrons is as a background for smaller azaleas and other flowering shrubs. R. catawbiense and R. maximum, for instance, give a towering contrast of greenery and their extensive growth must be strongly anticipated in the planting scheme. R. minus and R. californicum reach medium height. Most of the other species seldom go above 6 feet in cultivation and can therefore be used for intermediate background, as space fillers, for contour planting or for accent groups. (See Chart 4).
        Another native, Kalmia latifolia, the largest of the laurels, grows to about 10 feet and is often used for background-either alone or intermixed with rhododendrons and/or other evergreens. The low mountain laurel Kalmia augustifolia places well in small areas, since its height is about 2-3 feet. It is a bit more formal than the feathery hemlock, and the small leaves help to vary the general pattern. It has a tendency to become scraggly, however, and needs occasional pruning.
        The hollies offer a wide specific variation in the degree of formality and in climatic adaptability. One which makes a handsome semi-formal background and also serves well for accent is the Chinese holly, Ilex cornuta - especially var. burfordi. Being tolerant of severe pruning, it is therefore valuable as a source of greenery for the house. Its unusual appearance creates much attention. For good compact forms, use the Japanese species Ilex crenata, varieties bullata and rotundifolia.
        Four other broad-leaved, flowering ericaceous shrubs of considerable importance are two Leucothoes - L. axillaris and L. catesbaei, and the Pieris - P. floribunda and P. japonica. The plants are of general similarity in flower form. The white flowers are borne in long clusters or racemes, pendent except P. floribunda, giving a restful contrast against the leaves. Foliage turns bronze in the fall. The Leucothoes and P. japonica ordinarily grow to about 6 feet, while P. floribunda reaches about 4 feet. Except for tall background, we can choose from among these plants one which will serve for almost any requirement -foundation planting, intermediate background, filler, accent, foreground, border, etc. The white flowers and the unusual foliage can be used to tone down heavy masses of brilliant color. They can separate color extremes in close planting. And they serve well for breaking color continuity. These shrubs deserve more frequent use.
        A very versatile shrub of varying height (4 to 10 ft.) is Mahonia aquifolium, or Oregon Grape. The dwarf form, M. nervosa, is still too difficult to obtain, but its demand will increase rapidly.
        Although the feathery, pendent branches of the hemlock either Tsuga canadensis or T. caroliniana mark it as the most suitable of all native conifers for companion planting with azaleas, nevertheless the more formal spruces should not be denied a place in the overall planting scheme. They can be well employed for occasional sharp accent. They also establish a focal point at the far end of a long vista. They should not be placed alone, as specimen plants, in an informal garden. Those forms with dark green needles makes the best background for the bright-colored variants of Azalea calendulacea. The native black and red spruces especially, and to some extent the Norway spruce, are of this type. They are not quite so formal as the Koster and Colorado blue spruces and some of the other fine species, mainly because their branches are more drooping and they are less compact. Several of the cultivated varieties of dwarf spruce, even though rather formal individually, can serve well in certain close groups.
        There are available many types of evergreens, both broadleaved and coniferous, from which can be selected several that would be suitable for almost any environment or requirement. Only a few of these have been mentioned.
        Spirea vanhouttei, because of its profusion of white bloom, produces a stunning effect when planted as intermediate background for or intermixed with yellow and orange azaleas. Where space is limited, some pruning is necessary. A somewhat objectionable feature, however, is that it is sometimes host to aphides and then must be carefully sprayed.
        The forsythias, universal favorites because of early and showy flowering, are often found in informal plantings with azaleas, even though (with one exception) no azalea blooms at the same time. Their light green leaves supply good contrast and they can be pruned to serve many purposes. In fact, severe pruning (after bloom) is essential to keep this shrub within bounds, as well as to encourage profuse flowering. Several varieties are available.
        There is a vast list of other shrubs that are popular in various parts of the country for mixed planting. You should be familiar with those in your area. Don't plant promiscuously, but study habits of growth and color compatibility. Consult the local nurseryman. To mention a few: deutzia, kolkwitzia, chaenomeles, abelia, hydrangea, winterberry Ilex glabra, certain viburnums and ligustrums, weigelia and many others.
        As the title of this article would suggest, there is no description or charting herein of the hundreds of non-native azaleas and the hybrids from certain species-both deciduous and evergreen-that could be used in a planting scheme to broaden the blooming period. That would be a sizeable discussion in itself. Suffice it to say that in all rhododendron zones of North America, except zones 3 and 7, a large selection of such azaleas, with wide color range, can be successfully grown. In zone 3, selection is small but color range appreciable. Most nurserymen who handle these azaleas can advise you wisely. The same applies to the various hybrid rhododendrons.
        Azaleas are probably the most popular of the native shrubs-and for many reasons. They offer the greatest range of color. They are generally easy to obtain in their respective group areas. They are comparatively tolerant of extremes-full sunshine, exposure to wintry winds and excessive cold. Certain species thrive in a dry, warm climate. With surprisingly little attention they grow well and bloom heavily, although proper care always pays. Responding well to correct fertilizers, they nevertheless prosper without any if roots are mulched and soil kept slightly acid. In short,

CHART 1. NATIVE RHODODENDRONS & AZALEAS - Color Compatibility and Zonal Use
Symbol No. Rhododendrons
(Cold hardy)
Hardiness Approx. Blooming Period
Upper Appalachian Area
(Upper Zone 4)
Thrives in
Rhododendron
Zone*
carolinianum AA Mid May 3, 4, 5
  (rose, rosy-pink, rosy-purple)      

2

carolinianum album

AA

Mid May

3, 4, 5
  (white)      

3

catawbiense

AA

Late May-June

3, 4, 5
  (orchid, rose-pink, purplish rose)     6 in part

4

minus

AA

June-July

3, 4, 5
  (magenta-pink, purplish-rose)      
5 maximum AA Late June-July 3, 4, 5, 6
  (white to light pink)      
Plant with
Rhododendron
Symbol No.
Azaleas
(Cold hardy)
Hardiness Approx. Blooming Period
Upper Appalachian Area
(Upper Zone 4)
Thrives in
Rhododendron
Zones*
1, 2, 3, 4, 5 canadensis AA Late April-May 3, 4, 5
  (lavender-pink)      
1, 2, 3, 4, 5, vaseyi AA Late April-May 3, 4, 5, 6, 8
6, 7, 8 (shell-pink)      
(Chart 2)        
1, 2, 3, 4, 5, 6 atlantica A April-May 3, 4, 5, 6 in part
(Chart 2) (white & pink)      
1, 2, 3, 4, 5, 6 nudiflora AA Early May 3, 4, 5, 6, 8 in part
7, 8 (pink)      
(Chart 2)        
1, 2, 3, 4, 5, 6 rosea AA Early May 3, 4 5, 6, 8
7, 8 (rose-pink)      
(Chart 2)        
(1), 2, (3), (4) calendulacea AA Late May 3, 4, 8
5, 7, (8), (yellow, orange, red)   Late June  
(Chart 2)        
1, 2, 3, 4 cumberlandense A or AA June-July 3, 4, 5, 6 in part
5, 6, 7, 8 (deep red, scarlet, orange)      
(Chart 2)        
1, 2, 3, 4, arborescens AA Mid June 3, 4, 5, 6, 8

5, 6, 7, 8

(white & pinkish)      
(Chart 2)        
1, 2, 3, 4, 5 viscosa AA June-July 3, 4, 5, 6, 8
5, 6, 7, 8 (white)      
(Chart 2)        
 Will vary according to severity of change in climatic conditions.
* With minor exceptions, endemic to bold zones only (right column). See "Lone designations."
+ No bloom overlap with rhododendron No. 4 in some environments.
(1) (3) (4) (8)  With calendulaceum of clear red, clear or pale yellow only.
3 4 6 8  With cumberlandense of deep red only.
 
CHART 2. NATIVE RHODODENDRONS & AZALEAS - Color Compatibility and Zonal Use
Symbol No. Rhododendrons
(mild climate)
Indicated
Hardiness Approx. Blooming
Period in Zones
Indicated
Thrives in
Rhododendron
Zone*
6 chapmanii
(rose-pink)
C Early May (6) 6
7 albiflorum
(white)
C July (8) 7, 8
8 californicum
(pink or rosy purple)
B Mid-May, Mid-June (8) 6, 8, lower 5
Plant with
Rhododendron
Symbol No.
Azaleas
(mild climate)
Hardiness Approx. Blooming
Period in Zones
Indicated
Thrives in
Rhododendron
Zone*
3, 4, 5, 6, 8
(Chart 1)
canescens
(pinkish and white)
C Late Jan.
Feb-Mar-Apr. (6)
6, lower 5
(3), 5, (6)
(Chart 1)
austrina
(cream, yellow, orange)
C Mid-March, Apr. (6) 6, lower 5 in part
3, 5, 6, 8
(Chart 1)
alabamensis
(principally white)
C April-May (6) 6, 5 in part
3, 5, 6, 8
(Chart 1)
oblongifolia
(white)
C April-May (6) 6
1, 2, 3, 4, 5, 6 (Chart 1) speciosa+
(scarlet, bright red)
B April-May (6) 6, 5 in part
2, 5
(Chart 1)
fastigifolia
(scarlet)
B May-June (6) 6, 4, 5 in part
7, 8 occidentalis (white, rarely pinkish) (yellowish blotch upper lobe) C May-June-July (8) 8, 6 in part
1, 2, 3, 4, 5 6, 8 (Chart 1) furbishi
(pink)
B or A## June (6) 4, 6, 5 in part
ã ã
1, 2, 3, 4, 5, 6 (Chart 1)
bakeri
(yellow, orange-scarlet)
B or A## June-July (6) 4, 6, 5 in part
3, 5, 6, 8
(Chart 1)
serrulata
(white or flushed)
C June-July-Aug (6) 6, lower 5 in part
v
1, 2, 3, 4, 5, 6 (Chart 1)
prunifolia
(crimson-orange-yellow)
B or A## July-August (6) 3, 5, 6, 4 in part
# Will vary according to severity of change in climatic conditions.
* With minor exceptions, endemic to underlined zones only (right column. See Zone designations.
^ ^ ^ ^
1, 3, 4, 6 With speciosa of bright red only.
(3), (6) With austrina of light yellow and cream only
## Hardiness not thoroughly established in Zones 3 and 4.
v
4 With prunifolia of crimson or pale, clear yellow only.
ã ã
3 4 With bakeri or pale, clear yellow only.
+ No bloom overlap with rhododendron No. 4 in most environments.

        Deciduous azaleas are thoroughly dependable and are adaptable to many adverse environments. Start with just a few, using proper companion plantings, and you will soon become so interested in azaleas that you will have them in your garden for the rest of your life. Arlington, Va.

COMMENTS ON CHARTS 1 AND 2

        These charts indicate zones in which each plant can be successfully grown. Collectors and others specializing in rhododendrons and/or azaleas can properly cultivate certain plants not naturally adapted to the area. However, it is advisable for most persons to base the selection upon four factors primarily.

        First: Determine which plants are native to your zone.

        Second: Select any additional species from zones in the climate range generally similar to yours.

        Third: Determine availability.

        Fourth: Consult local nurserymen, particularly those specializing in rhododendrons and azaleas. For instance, if you live in Zone 6, your climatic area is represented by Chart 2. On Chart 1, Azalea nudiflora is shown as satisfactory for parts of Zone 6. You should use your native and similar species, A. canescens, instead. Observe that R. maximum and R. catawbiense are indicated as companion plants for A. canescens. The first is native to Zone 6. Your local nurserymen may advise that R. catawbiense, however, is not entirely suitable to your particular environment. It is shown "6 in part" on Chart 1.

        It should be noted that the charts mention rhododendrons and azaleas separately. Botanically, azaleas are classed in sub-series groups under genus Rhododendron. For simplicity, the azalea designations are used so that the average reader can recognize them when so listed by the majority of the nursery trade.

CHART 3. RHODODENDRON ZONE DESIGNATIONS1
Zone Geographical Area
3 Northeastern States and Southeastern Canada
4 Appalachian Area
5 Atlantic Coastal
6 Southeastern States
7 Rocky Mountain
8 Pacific Coastal
(1) Based upon Appendix C , Rhododendrons and Azaleas, page 462-1936, Clement G. Bowers

 

CHART 4. APPROXIMATE HEIGHTS (In Cultivation)
Rhododendrons Azaleas
3-6 ft. 1½-3 ft.
carolinianum, catawbiense f. compactum, chapmanii, albiflorum canadensis, atlantica, alabamensis
6-10 ft. 3-6 ft.
minus, californicum nudifiora, rosea, speciosa occidentalis, oblongifolia, austrina, viscosa, fastigifolia, furbishi
6-15 ft. 6-12 ft.
catawbiense, maximum, calendulaceum arborescens, vaseyi, canescens, cumberlandensis, serrulata, prunifolia, bakeri
Under very favorable conditions, certain species in some instances will exceed
normal heights given above.


Volume 7, Number 3
July 1953

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