Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA CALIFORNIA AGRICULTURAL Experiment Station Extension Service MANUAL 21 7, HERE IS no exact botanical distinction between rhododendrons and azaleas. Both belong to the genus Rhododendron. The common name "rhododendron" is applied mainly to the evergreen species with large, bell-shaped flowers, while the common name "azalea" is arbi- trarily applied to certain species and their hybrids, both evergreen and deciduous, with flowers that are relatively smaller, usually flared or funnel shaped. Nursery catalogs list the varieties under separate headings, with indi- cations whether the varieties are evergreen or deciduous. This is also done in the tables appearing at the end of the manual. CONTENTS Climate, Location, and Soil Needs 1 Preparing the Soil and Planting 1 Watering and Fertilizing 2 Pruning 3 Potting Techniques 7 Propagation 8 Diseases 12 Pests 16 Selection of Varieties 18 References 30 Tables 31 I ■JC O CO 1 cc i UJ ! > CO CD >- *~~ QC CD & T-i QZ a. CQ -* <£ FOR THE AMATEUR H. M. BUTTERFIELD UNIVERSITY OF CALIFORNIA • DIVISION OF AGRICULTURAL SCIENCES Agricultural Experiment Station — Extension Service LIBR ARY UNIVERSITY OF CALIFORNIA DAVIS Rhododendrons may be grown in the filtered shade of pine trees. The pine needles are used as mulch. THE AUTHOR: H. M. Butterfield is Agriculturist Emeritus, Agricultural Extension Service, Berkeley. MAY, 1956 Rhododendrons and Azaleas Have Specific Needs in Climate, Location, and Soil Climate. A moderately cool climate, free from excessively hot sunlight, is best for rhododendrons and azaleas. Where winter months are very cold only hardy varieties should be planted. Most rhodo- dendrons and azaleas can stand the ordi- nary winters common to the valleys and the coastal areas of California. However, the Indian azaleas do not grow very satis- factorily in cold climates; and many of the popular evergreen azaleas are sensi- tive to frost at flowering time. Some con- sideration must therefore be given to winter temperatures. Location. Both rhododendrons and azaleas need a location that provides sun half the day, yet offers protection from hot afternoon sun. Some azaleas need shade almost continuously if they are to grow and flower well. Neither group should be exposed to wind or drafts. Rhododendrons can be planted in the filtered shade of pine trees. Against this backdrop their foliage and blossoms are strikingly beautiful, and the plants like the mulch of pine needles. Soil. A well-drained, slightly acid soil is best, although rhododendrons and azaleas do fairly well in California soils that are about neutral in reaction if other growing conditions are favorable. It is more important for the soil to be well fertilized, drained, yet supplied with moisture at all times than for it to be acid. Planting Depends on Two Steps: Preparing the Plant and Preparing the Soil The time to set out rhododendron and azalea plants in most parts of California is from January to March. This is just before new growth pushes out but after the soil has dried enough to permit easy working. The plant. Some plants are sold in cans or pots, but most come from the nursery balled — that is, the soil is left around the roots and covered with bur- lap. If the ball of earth has dried out, it should be soaked in water for several hours before it is planted. Soaking the entire ball in a tub of water before plant- ing is more satisfactory than attempting to water the plant sufficiently after plant- ing. The string which ties the burlap around the crown of the plant is cut, but the burlap itself is left around the ball. The soil. The planting hole should be a little larger than the ball of earth encas- ing the roots. A hole 18 x 18 inches is large enough for the usual small rhodo- dendron plant. Plant no deeper than nec- essary to cover the roots. Fill in the hole with a peaty or leafmold soil mixture. Well-rotted leafmold from the oak, ma- drone, and redwood, which generally is acid, is suitable. A mixture of 2 or 3 parts loam, 1 part peat or leafmold, and 1 part sand may be used, or equal parts of leafmold and soil. Firm the soil mix- ture and after planting, water well to settle the earth about the roots. New roots should start within a few weeks. Pruning is not necessary at planting. [i] If the soil is heavy, drainage can be improved by mixing in leafmold or peat moss well in advance of planting. The rooted cutting. Both rhododen- dron and azalea cuttings which are rooted by any of the propagation meth- ods, when ready, are planted in the same preparation of soil as the balled or canned specimen. The size of hole is gauged by the size of the rooted cutting. Watering. The soil mixture for rho- dodendrons and azaleas should never reach the wilting point — that is, where the growing tips remain wilted for longer than 12 hours. Enough water is given to moisten the deepest roots. To maintain adequate moisture about the roots during dry summer months, water twice a week in locations near the coast and more often farther inland. Each year a new mulch of moist leafmold, pine needles, or peat moss placed about the plants will keep the surface roots cool in hot weather. This mulch needs frequent watering. Weeding. No cultivation is required for either rhododendrons or azaleas, but all weeds should be removed. Fertilizing. Older rhododendron and azalea plants need fertilizing. Soil norm- The balled plant is placed in the hole. The en- circling space is filled in with leafmold and soil. Cultural Practices for Both Rhododendrons and Azaleas Emphasize Watering and Fertilizing ally deficient in nitrogen may be fertil- ized from time to time with limited amounts of cottonseed meal, blood meal, fish meal, fish oil emulsion, or tankage. Nitrogen should be in the form of am- monia rather than nitrate, since nitrate tends to cause yellowing of the leaves and poor plant growth. Ammonium nitrogen, which is liberated slowly over a period of time, is usually absorbed by the plants in the form of ammonia. The continued use of barnyard manure is objectionable unless an acid-forming material is used to neutralize excessive alkali. However, a small amount of cow manure occasionally used around rhodo- dendrons aids in maintaining good growth. The soil reaction may range between pH 5.0 and pH 5.5, although it is known that some of our native rhododendrons and azaleas are thriving in soils that are alkaline. A considerable latitude in the range of pH value is permissible. Cotton- seed meal has served well as a fertilizer. If an acid-type fertilizer is used and we know that rhododendrons and azaleas tolerate an acid soil condition, the fol- lowing acid-type mixture, which checks closely with a 4-6-8 fertilizer mixture, may be used: Pounds Superphosphate 35 Cottonseed meal 28 Potassium sulfate 17 Ammonium sulfate 10 \luminum sulfate (to acidify mixture) 10 100 [2] It is rarely possible for the home gar- dener to test his soil for soil reaction or lime content; however, soil chemists may be hired to make such a test. With our present knowledge that azaleas and rho- dodendrons tolerate a wide range of pH value, it is impossible to say definitely that a certain range is essential. If there is a high lime content in the soil it may lead to a form of chlorosis and plant decline. Such an unfavorable soil condi- tion may need correction or the plants may need to be transplanted to a more favorable soil. Acidifying materials may be added in some instances to overcome damage from high lime content or some of the iron chelates may help insure ade- quate iron. Fertilizer is applied at the rate of 1 teaspoon of a 6 per cent nitrogen fertil- izer for a well-established plant with a 6-inch spread. This amount should ade- quately maintain healthy growth. The application may be repeated at intervals of eight weeks during the early growing season. The practice of adding commercial aluminum sulfate at the rate of % to % pound per square yard of soil surface to acidify the soil has been popular in re- cent years. As a permanent practice this is somewhat questionable, because free aluminum may injure the roots of rhodo- dendrons and azaleas. Theoretically, some acid-forming ma- terial such as sulfur, which does not con- tain aluminum, is a better selection. Ammonium sulfate serves the same pur- pose, but since it would probably be changed quickly to a nitrate, it would be less satisfactory than certain other chem- icals which would be changed to a nitrate form more slowly. Acid potassium sul- fate, acid phosphate, and tannic acid have been suggested for trial. Sulfur may be applied in moderation in the late fall to help produce an acid condition of the soil. It is more effective than aluminum sulfate as an acidifier, although the latter reacts more quickly. Only about half as much sulfur as alu- minum sulfate is necessary to produce correct soil acidity. Saving the declining plant. Rho- dodendron and azalea plants beginning to decline usually can be saved. If the ex- posure is satisfactory, the plant may be lifted in the fall or late winter, before new growth pushes out, and the soil renovated. Sometimes a good surface mulch and a dressing of fertilizer are sufficient without lifting the plant. If the plant is in the wrong location, however, it should be moved to a more suitable place in the garden. No soil treatment or change of location will take the place of liberal watering. Pruning Regulates Size or Height, Maintains Good Flowering, and Eliminates Unsatisfactory Parts Try to keep the pruning goals in mind while cutting, especially when shaping. This is difficult when cutting to eliminate diseased, weak, or dead parts. Adapt pruning to the growth habits of each plant. RHODODENDRONS Tall rhododendrons. Only a few home gardens have room for the older popular varieties, such as Pink Pearl, Alice, and Cynthia, which usually grow to a height of 6 feet or more. The grower may have been told that these rhododen- drons should not be pruned. This is only partly true. Certainly such varieties should be shortened-in a little each year to keep the plants from becoming tall and leggy, but not more than a third of the branches are cut back in any one year. [3] At this rate of pruning, it would take almost three years to shorten an entire plant. If pruning is judiciously done each year — cutting back of only a few of the taller canes— there should be no need for very heavy pruning in any one season. At about the time the flowers begin to fade and just before rank new growth pushes out, the canes to be pruned are cut back just above a bud. On such vari- eties as Alice and Pink Pearl the actual time of pruning should be in early May. (See table 3 for height and blooming period.) A healthy plant sends out a new shoot from the dormant bud just below the cut, and this new shoot may need two or three years in which to form normal flower buds, although healthy flower buds can be expected to appear ultimately on all such canes that are cut back. By limiting the amount of annual cutting to a moderate pruning it will be possible to have a satisfactory crop of blooms each season. At the same time, taller rhododendrons will fit more pre- cisely into the space available and the blossoms will be seen to much better advantage. Very old canes that are weak or diseased should be removed at the point of origin on the main branch or trunk. Irregularly shaped rhododen- drons. Not all rhododendron varieties are regular in shape. For example, Fra- grantissimum is one of the Himalayan hybrids resulting from a cross between Rhododendron ciliatum and R. edge- worthi. The plant of this hybrid is in- clined to be irregular in shape unless it is properly pruned from the time it is small. By pinching out a branch tip here and there during the first two or three years, it is possible to train the growth into a well-shaped shrub. As the plant reaches blooming size, pinching-out should be discontinued, except for an occasional branch that must be short- ened to retain the compact form of the plant. Usually this hybrid and its rela- tives respond well to light pruning (table 3). Compact species. Another group of rhododendrons produced by hybridizing Rhododendron augustini and similar species has furnished gardeners with such popular varieties as Blue Bird, Blue Diamond, and Blue Tit, which reach a height of 6 feet. The bushes of this group become compact and form clumps cov- ered with flowers. As the plants reach full maturity, shoots occasionally weaken and produce thin, weak-flowering twigs. When this happens, the entire branch should be cut back to ground level and replaced by new shoots. This group of rhododendrons will even tolerate shear- ing at any arbitrary height, although it is better to thin out weakened old branches than to cut back blindly. Dwarf rhododendrons. Still an- other group of rhododendrons includes the dwarf species and hybrids listed in table 4. These small shrubs tend to form a mat or thicket, and may be grown in a rock garden or in front of taller kinds. Their size and height should be con- trolled to fit the environment. Many of these shrubs are weakened by seed forma- tion. The plant may be headed back slightly as the blooms fade. If it has too many dead or weak branches, the entire plant should be cut back just above ground level and a new head allowed to form. In this group of dwarf plants cut- ting back to just above ground level is better than trying to thin out the growth. AZALEAS The azalea fancier usually tries to select species and varieties that easily conform to a planned size and form, but he may also do some pruning and shap- ing to insure this. The plant may be left to take its natural shape or it may be pruned and trained to a standard, to a cascade, or to espalier form. Gardeners with limited time should not try to prune and train plants into [4] / > ." w. ~:&tf---yy*/-X'-%p;.: >// ^ > to 3 inches long, arc taken in the early growing sea- son at about the time the flowers fade. Rhododendron cuttings should be longer r opposite page) . Cuttings may root in as short a period as three to four weeks or may take up to six weeks in a greenhouse, depending upon the growing conditions and the na- ture of the cutting used. Temperature and humidity must be carefully controlled. An electric hotbed and frame are usually essential, with a bottom temperature of 70° to 75° F. The rooting medium may be a mixture of coarse river sand and sifted peat — or a similar mixture — that is slightly acid in reaction. Frequent sprinkling during the rooting period may be necessary to keep the cuttings from drying out, especially when the outside air is dr\ . Layering. Some amateurs root cut- tings outdoors but cuttings will probably take a jrear <>r more to root, whether [81 Type of growth that should be used for making a rhododendron cutting. An evergreen azalea showing new growth suitable for making a cutting. IF YOU DO TRY TO PRODUCE YOUR OWN, USE CUTTINGS Rhododendron cuttings rooted in a flat and showing new growth. Lower leaves were cut to allow more room in flat. HERE ARE THE STEPS Rhododendron cutting with well-developed roots. Roots undeveloped are easily damaged in transplanting. Left, rhododendron cutting with established roots, ready to set out; right, azalea cutting rooted and plant pinched back for compact form. started outdoors or inside a house. A quicker and more certain method for the amateur is to layer a low branch for rooting. With the stem notched or girdled just below the point where roots should appear, then covered with moist soil, roots form after several months up to a year. The rooted layer may then be re- moved and treated like a rooted cutting. Air-layering. This means of propa- gation has come into use for species and varieties of both rhododendrons and azaleas that are very difficult to root from ordinary cuttings. A plastic wrap is lined with moist sphagnum moss, and the inner side is dusted with a hormone powder which aids root formation. The sphag- num moss should be thoroughly wet, then squeezed fairly dry before it is placed in the plastic wrap. A healthy growing [10] tip on the plant is selected. Its bark is either girdled just below the point where roots should form or a tongue is made on either side, cutting back about l 1 /^ inches toward the tip. The tongue is held apart with a small wooden match or piece of wood so that the cut edges will not grow together quickly. The aerial wrap is finally placed around the stem in the area where roots are expected to develop, and is tied snugly above and below. The sphagnum moss should re- main moist for at least three months. Under favorable conditions, roots will form in the zone of the girdle or tongue, and the wrap can be removed. The aerial cuttings are then severed and treated like any rooted cutting. This method of prop- agation is used during the early growing season when the wood is soft. If the wood is too hard, the air-layered tip will not root readily, if at all. Perhaps air-layer- ing should be limited to plants which are not easily propagated in any other way. Grafting. The method for grafting is essentially the same for both rhododen- drons and azaleas. A shaded greenhouse or propagating frame is used. Here, A healthy growing tip on the plant is chosen for the placing of the plastic wrap. [ii] under glass, temperature and moisture are more easily controlled than in the open. For grafting rhododendrons, seedlings of certain popular species, such as Rho- dodendron ponticum, are grown and transplanted to pots. R. maximum and R. catawbiense have also been used suc- cessfully as rootstocks. Grafts known as saddle, veneer, or side may be used. If the wood of the rootstock is very hard, the graft will not take readily. Plants grown under glass or under lath for a few weeks in advance of grafting are more likely to develop a soft wood which is easier to graft. Winter-grafting will probably be more successful than sum- mer-grafting, although it is possible to veneer-graft successfully in summer. Air humidity is easier to control early in the year than during the dry summer months. The summer may be too warm for such grafting. Azaleas, especially the Belgian Indicas and the hardy Southern Indicas, are often grafted on a vigorous root, such as Vinacea Coccinea, a large, fast-growing single. Kurume azaleas do not have to be grafted. Grafting on a vigorous root- stock helps to insure a better root system, better growth, and more buds and flowers. Diseases* of Rhododendrons and Azaleas Are Caused Chiefly by Soil Conditions or Soil Microorganisms The causes of rhododendron and aza- lea diseases frequently can be corrected by changing the cultural conditions under which the plants are growing. There are, however, several diseases and a permanent wilting. The main stem turns brown at the soil line; a cut into this area reveals only dead bark and wood. Since this disease usually attacks only which attack the aboveground parts of young plants growing in excessively wet the plant and these are controlled by chemical sprays. As was mentioned before, both rho- dodendrons and azaleas do best in a light, well-drained soil. Since many Cali- fornia soils are heavy, with a high moisture-holding capacity, planting in them usually results in serious problems. Water-mold root rot. Under ex- tremely wet soil conditions a group of soil fungi known as water molds will at- tack the roots and crown area of young plants and cause a disease known as wilt, root rot, or water-mold root rot. Af- fected plants wilt and the leaves become a dull green. This is followed by leaf drop * Section on diseases by Robert D. Kaabe, Assistant Professor of Plant Pathology and \ -istant Plant Pathologist in the Experiment Station, Berkeley. soil, it is easily controlled by providing good soil drainage before the plants are set out. In a heavy soil it is especially advisable to avoid digging a hole or pit even though it is to be filled with a soil mixture of the desirable type for the plant. Such a hole acts as a pocket to catch the water and provides the condi- tions favoring disease development. Other control practices include adjust- ment of the soil pH to between 4.5 and 5.5 and avoidance of planting too deeply. Armillaria root rot. A disease also favored by wet conditions is oak root fungus or Armillaria root rot. Infected plants are unthrifty in appearance, and frequently go into a permanent wilt. The disease is most easily diagnosed by cutting into the bark of the crown and larger roots. If the fungus is present, there are large white fans or plaques be- [12 J Oak root fungus, or Armillaria root rot, is indi- cated by white fans or plaques between the bark and the hardwood. (Courtesy Department Plant Pathology.) tween the bark and the hard wood and frequently small, dark, shoestring-like strands on the outside of the bark of the infected roots. Mushrooms in the late fall or early winter are another indication of the fungus. Once the oak root fungus becomes established, it is very difficult to control. In a diseased area, the plants can be re- moved and the soil treated with carbon bisulfide. This treatment is hazardous in garden areas where plants are grown close to one another, however, because the chemical will kill all the plants or roots in the treated area. Exposing the crowns of infected plants to air may help to prolong the plant life since the fungus cannot exist under dry conditions. Be- cause the fungus does thrive in wet, heavy soils, improving the drainage and avoiding too much water will help to pre- vent infection. The question has frequently risen as to whether or not the oak root fungus can be introduced by leafmold brought into the garden. There is little chance of its being in leafmold which consists en- tirely of leaves but if any woody material is included it may be present. If in doubt about leafmold, spread it out and let it dry thoroughly before using it. The oak root fungus cannot tolerate dry conditions and will die. Rhizoctonia cutting and graft de- cay. Another soil-borne disease problem is cutting and graft decay which results from infection by the soil fungus Rhizoc- tonia solani. In moist cutting or grafting frames, this fungus attacks primarily the tops of the plants and grows over the leaves and stems as a cobwebby growth. Under moist conditions it will cause a decay of the infected plant parts, while under drier conditions it may cause a rot at the base of the cuttings. It is con- trolled by using sterilized soil or sand in the cutting beds and by avoiding the use of too much water. If the disease does break out, a drenching with thiram will help to control it. Lime -induced chlorosis. Several diseases are the result of a soil condition rather than the attack of a disease-pro- ducing organism. One of these is known as lime-induced chlorosis, or simply chlorosis. In this disease, the leaves, par- ticularly those at the tip of new growth, turn pale green or even yellow. Fre- quently the leaf margins and the tissues between the veins turn a lighter color while the veins retain the darker color. Lime-induced chlorosis is caused by a soil condition that is produced by too much lime or too basic a soil reaction. This makes certain elements, particularly iron, unavailable to the plants. This can be corrected temporarily by sprinkling sulfur on the soil around a plant or by spraying the leaves with iron sulfate (% part, by weight, to 100 parts of water). Spraying the leaves with iron sequestrene (as directed by the manufacturer) is also an effective control. None of these controls is permanent and must be repeated. A more lasting [13] control is the incorporation of organic material, such as peat moss or well-rotted leafmold, into the soil. Salt injury. Salt injury is another disease resulting from a soil condition and frequently is common where plants are grown in containers. The symptoms include browning and death of the tissues around the margins of the leaves. Fre- quently leaves may yellow and on some plants small dark or purplish warty growths or bumps may appear on the under surfaces of leaves. Salt injury is controlled by giving the plants an oc- casional heavy watering to leach away excess salts which have accumulated in the soil. If the plants are in small con- tainers and can be handled easily, soak- ing them overnight in a tub of water is effective. Root injury. Frequently root injury results from hoeing or cultivating the soil around azaleas and rhododendrons. These plants are surface feeders — mean- ing the roots which absorb water and nutrients are found very near the surface of the soil. Therefore, it is best to disturb the soil around the plant as little as pos- sible. Sun scald and leaf spots. One dis- ease arising from troubles aboveground that is more prevalent some years than others in sun scald. This is found more often on rhododendrons than on aza- leas. It appears as large brown areas in the center of the leaves. Sufficient shade is the best control. Certain varieties stand more sun than others; this should be considered when setting out plants. Hardening off new plants from nurseries frequently prevents injury to the leaves. Although sun scald in itself may not be too serious, the injuries it causes look bad. Furthermore, injuries allow the entrance of certain fungi — weak para- sites — which do not enter healthy plants, but having gained a foothold are capable of causing great damage. Several fungi are found associated with injuries resulting from sun scald, excess salt, insects, and fungus infections. These fungi produce spots on the foliage p " ll4, V BP^^ ■ 'Sa^Sk * v'^JP^^ ^p^^ _,.. 2. „ ^^^ a '#» w ^ (#*' :: ''' ■ ; ^?^B T% ,»• iQ&/^M Sun scald appears as large brown areas in the center of rhododendron leaves more often than on azalea leaves. (Courtesy Department Plant Pathology.) : 4t* : ;:. '%< Azalea leaf scorch produces dark, reddish- brown, angular areas on the leaves, which fall prematurely. (Courtesy Department Plant Pa- thology.) [14 1 ^ w W mMmm? Azalea petal blight appears as small pale spots on the inner surfaces of colored petals and as brown spots on white petals. (Courtesy Department Plant Pathology.) which are silver gray on the upper sur- face and light brown on the lower sur- face. The upper surface may be dotted with small black spots which are the fruiting bodies of the organisms. Silvery spots may also be produced on the stems. Control is brought about indirectly by avoiding sun scald and salt injury and by controlling insects and disease-pro- ducing fungi. Leaf scorch. A fungus disease of aza- leas known as leaf scorch is sometimes found in California, especially in wet seasons or in foggy areas. The disease, resulting from infection by a fungus known as Septoria azaleae, appears as dark, reddish-brown, angular areas on the leaves and causes them to fall pre- maturely. Although not nearly so preva- lent, there is a similar disease on rhodo- dendrons caused by a closely related fungus. These fungi are controlled by spraying with either Bordeaux mixture (2-2-50) or ferbam at about two-week intervals as the new leaves expand during the growing season or when the diseases appear. Destruction of the fallen leaves helps to prevent spread of the fungi. Azalea leaf gall. One of the more common diseases of azaleas, which at times may be serious, is the azalea leaf gall. This disease is the result of a fungus infection which causes the leaves to be- come thickened and fleshy, either wholly or in part. The infected areas in the leaves turn pale green, pink, or white. The [15] flower parts of some species may trans- form into hard, fleshy, waxy, irregular galls. The infected parts later may be covered with a white bloom which con- sists of spores of the fungus. Control by removing and destroying the infected parts. Spray with a weak Bordeaux (3-1-50) or zineb. Azalea petal blight. The most seri- ous disease attacking azaleas is azalea petal blight, also known as azalea flower spot and Ovulinia flower blight. Although found only in nurseries for many years, it recently has been reported occurring in home plantings in California. The dis- ease is found primarily in the south- eastern part of the United States, where it is particularly severe on azaleas of the Kurume and Indian types. The fungus causing this disease attacks only the flowers of the azaleas and, infrequently, the flowers of closely related plants, such as rhododendron and mountain laurel. Azalea petal blight appears as small pale spots on the inner surfaces of the petals of the colored flowers and as brown spots on the white flowers. These spots rapidly enlarge until the whole flower collapses. The rot produced is very soft and mushy in contrast to Botrytis rot of old flowers, which is a dry rot. Eventually the flowers collapse and fall. In the diseased flowers small, dark, flat, or cupped structures develop. These are the resting bodies of the fungus, which serve to carry it through seasons when the azaleas are not in flower. They fall to the ground with the flower and re- main there until weather conditions favorable to the flowering of the azalea again are present. At this time they germi- nate to produce little cups from which spores are shot. These spores, once on an azalea petal and in the presence of moisture, germinate to produce an infec- tion. Secondary spores form in the in- fected flowers to spread the disease under favorable conditions. Azalea petal blight is controlled by avoiding overhead watering while the plants are in flower. If the disease be- comes established, spraying the flowers three times a week with zineb plus a spreader-sticker helps in the control. Re- moving and destroying diseased blos- soms tend to keep the resting stage from carrying the fungus from one year to the next. Covering the beds with several inches of mulching material also helps to keep the resting structures free of spores. Indoor potted plants, which are so dif- ficult to spray, should be especially pro- tected from this disease. However, by growing azalea plants under conditions of low humidity, the disease will not be- come established nor spread. Pests* Include the Privet Mite, Cyclamen Mite, Greenhouse Thrips, Azalea Leaf Miner, and Black Vine Weevil The azalea is host to all of these pests, and the rhododendron is attacked by some of them. Fortunately, not all of the pests appear at one time, and only a few justify much attention. However, gar- Section on pests by A. Earl Pritchard, As- sociate Professor of Entomology and Parasitol- ogy and Associate Entomologist in the Experi- ment Station, Berkeley. deners should recognize them and start adequate control if the pests appear. Privet mite (Brevipalpus inornatus) . In the adult stage this mite is bright red, with a central darkening that forms two eyelike spots. The privet mite appears on the undersurface of azalea leaves, and may be very destructive. The application of both sulfur and [16 lime sulfur has given satisfactory con- trol, as has a light oil containing ro- tenone. A light oil emulsion in 1 to 2 per cent strength should be safe when ap- plied on a day that is not too hot. Burn- ing may occur on young leaves if the spray is too strong or if the light oil emulsion breaks down in hot weather. Cyclamen mite (Stenotarsonemus pallidus (Banks)). This mite causes severe damage to azalea plants held a long time in the greenhouse. The cycla- men mite feeds on the new growth, where it aborts or deforms both leaves and flower buds. A greenhouse temperature range of 60° to 80° F seems to be highly favorable for this mite. Much less trouble has occurred under lath or in the open. The cyclamen mite has a fairly wide host range; this makes the mite hard to avoid completely. In areas where the cyclamen mite is troublesome, growers may find that it can be avoided more easily if the azaleas are set out in the open garden rather than kept under glass. Frequent hosing of the foliage with water may help to keep such pests from getting started. Try to avoid placing a newly potted azalea plant with other azaleas until its freedom from cy- clamen mites and similar pests is estab- lished. By starting with healthy plants the amateur should not be troubled with the cyclamen mite. Most nurseries have fa- cilities for adequate control, and since commercial growers sell only clean plants, those purchased from retail dealers should be healthy. Greenhouse thrips {Heliothrips hae- morrhoidalis) . This dark-brown thrips has lighter color on the back and has light yellow legs. The greenhouse thrips is commonly found on the underside of rhododendron leaves; it may also be found on azalea foliage. A bronzy or silvered appearance of the leaves usually indicates its presence. The gardener should observe the new crop of leaves carefully and apply a DDT or other suitable spray before the thrips have had time to do extensive harm. Once the leaves are badly damaged, they cannot be restored to good health, but in time will drop and be replaced with the new crop of leaves. If thrips are detected, spray with malathion, dieldrin, DDT, or lindane. Cover the underside of the leaves as com- pletely as possible. Azalea leaf miner (Gracilaria aza- leella) . This pest is often serious par- ticularly under greenhouse conditions. A DDT spray gives excellent control of the caterpillars. Black vine weevil {Brachyrhinus sulcatus) . Both the grubs and the adult beetles of this fairly common pest cause damage to rhododendrons and azaleas. Brachyrhinus sulcatus (black vine weevil) may girdle the roots and stem below the soil surface. [17] The insect is easily recognized by the kind of damage it does. Eggs dropped on the soil in summer hatch in about two weeks, and the grubs feed at first on the tender rootlets. By winter and early spring the grubs are large enough to at- tack the bark, and may entirely girdle the roots and stem below the soil surface. The grubs finally transform into adult weevils or beetles and emerge about May. Most of their damage is to the leaves, where they eat pieces out of the leaf margin. Spray with chlordane or dieldrin at the time the adults start to emerge in the spring (April or May in the San Fran- cisco Bay region). It is important to cover the surface of the ground with the spray. It is not possible to kill the grubs that are developing on the roots. Rhododendrons and Azaleas are Selected According to Hardiness, Color, Form, and Height SELECTING RHODODENDRONS More than 175 distinct varieties of rhododendrons can be purchased on the Pacific Coast at the present time, and new varieties are introduced each year. One rhododendron nursery alone is now growing as many as 250 varieties. This is a contrast to 1860, when such species as Rhododendron ponticum were being introduced into California. Hardiness. One of the requirements in selecting rhododendrons is hardiness to heat and to cold. A few varieties toler- ate full sun and are resistant to cold weather. Most varieties are reasonably tolerant of cold weather but need partial shade or at least protection from the hot afternoon sun. A third group thrives along the coast and can be grown in sheltered spots inland. Table 3 includes a column of hardiness for many old and new varieties. Color and form. Also important in selection are color, compactness, size, habit of flowers, and season of bloom. Fanciers generally prefer rhododendron varieties of good color and large flower trusses. Pink Pearl has been a popular variety with large flowers, but of a color thai tends to fade. Other varieties with similar large flower trusses are gradually forcing their way into popularity as they become available. Among those of supe- rior color and flower form are Alice, Betty Wormald, Gills Triumph, Loderi varieties, and Souvenir de Prof. Hugo de Vries. Height. Tall rhododendrons, such as Pink Pearl and Alice, have been a prob- lem in all but very large gardens. Easier to landscape are the low-growing or dwarf varieties which should have a place in the small home garden; they also can be planted to great advantage in large gardens in front of the tall varieties. Rock-garden fanciers may also be in- terested in some of the dwarf rhododen- drons listed by the nursery trade. Such species as Rhododendron anthopogon, R. calostrotum, R. chryseum, R. impeditum, R. fastigiatum, and R. hirsutum are being sold for rock-garden use. Dealers han- dling rock-garden plants may be con- sulted for additional names of dwarf species and varieties. Newer varieties. In past years, California nurserymen have listed mostly the older rhododendron varieties, which are moderately priced. With the intro- duction of many fine varieties from abroad, the better new varieties can now be purchased from nurseries in Califor- nia, Oregon, and Washington, although the price for newer introductions may be I 18] (Continued on page 27) VARIETY KEYNOTES FORM, HEIGHT, AND COLOR IN THESE SPECIMENS OF RHODODENDRONS AND AZALEAS All of the flowers and plants shown in this manual were photographed either in Golden Gate Park, San Francisco, or at the California Spring Garden Show, in Oakland. Florets of three varieties of Rhododendron Loderi show different form: Venus, King George, and Naomi. Rhododendron Mrs. G. W. Leak is a very popular medium growing variety. Rhododendron Elizabeth, a new 4-star English variety, was awarded highest certificate of merit at the 1955 California Spring Garden Show. It has red, bell-shaped florets. Rhododendron Fragrantissimum is a popular white-flowered fragrant hybrid. Bowbells is a rich pink rhododendron hybrid with bell-shaped florets, which is gaining in popularity. Simon Mardner, a very popular Indian azalea in rose red with lilac overtone. Has a long blooming period. Rhododendron Loderi var. Venus, a form with huge trusses of shell-pink flowers. This is a four-star English rhododendron. These are specimens of the brilliant coloring which azalea and rhodo- dendron flowers can give to a garden. The dark green foliage of healthy plants seems to deepen the rich colors. Rhododendron augustinii, an up- right, compact species with deep blue-mauve flowers about 2V2 inches wide. Rhododendron molle (Azalea mollis), a fine deciduous azalea with golden-yellow, funnelform flowers. «* Azalea Sweetheart Supreme is a pink-flowered variety with rather loose habit of growth. Azalea Snowdrift is a Macrantha variety with compact habit of growth. V ^ -g^. *. 1 fL^ates* > / ^* iiELak HwL .3 K * II . Kk ^Mg ' p%*^k ' E3fe ' ; l .... o - «%i &&m*i •' *fc b 5* *i Mm ' £ : Ute ^- , *; s / > r lk & - .s^ < * # Azalea White April is an Indica variety grown as a standard. ** *J^K^ &,# *: w M >, % M %4 wm^ ^o Azalea Alba Magnifica is an evergreen variety of Rhododendron magnificum (Azalea ledifolia) with fragrant white flowers. 4 Rhododendron Blue Peter is a 3-star hybrid unexcelled in its class and fine for planting in foreground. "J* VI %L i % >; \ '' s ^yS' ** *w V*- '4 k V ». it* • fK. £» 'i v St £ 'i^ i«r *■ *■ ~.C ><:r high. In time these new varieties are cer- tain to receive more attention from Cali- fornia gardeners ; in fact, many of them already are being purchased and planted by fanciers in California. Gardeners will insist on getting what they want, even if they have to obtain the plants outside California and at a price well above the average for the common varieties. Information about rhododendron va- rieties is found in catalogs issued by rho- dodendron specialists. The American Rhododendron Society publishes a year- book and quarterly bulletin for its mem- bers; some libraries may have reference copies. SELECTING AZALEAS In 1853, Warren and Son of Sacra- mento listed Rhododendron indicum var. Jxiteritium, R. molle, R. nudiflorum, R. pulchrum var. phoeniceum, and Azalea danielsiana (now associated with R. indicum). From this beginning, the list of species and varieties now known as azaleas has grown until today the fancier has no trouble in buying more than 50 distinct varieties and species. Evergreen azaleas are usually pre- ferred to deciduous, because their hand- some foliage clothes the plant when the blossoms are gone. However, deciduous azaleas also have a place in the garden, where their bright-colored flowers often come after many of the evergreen azaleas are through blooming. Deciduous azaleas really are dual-pur- pose: they are valued for their blossoms and also for their foliage, which may become highly colored before the leaves drop. Taller and more upright azaleas should be placed in the background, with lower, more compact forms in the fore- ground. When deciduous azaleas are in- cluded in the planting, combine them with evergreen plants to maintain green foliage in the garden during the dormant season of the deciduous plant. In selecting azaleas, the important fac- tors to consider are similar to those for rhododendrons : resistance to extremes of temperature and to wind; persistence of Rhododendron Loderi var. Venus is a massive bush of color at full bloom. X % :■ , ■:■ .■■:-. \4& *& M m* *Ntk foliage (evergreen or deciduous) and size of leaves; height of plant at matur- ity; flowering season and flowering habit (number of flowers on plant, color and size of flowers, and number of petals on flowers). Both single- and double-flow- ered varieties are available in most groups. Many of these characteristics are mentioned under the more important classes listed below. Azaleas have been divided into groups according to the species used in making certain crosses. The common names of azaleas are taken from place of origin or distribution, such as Ghent from Ghent, Holland, Kurume from Kurume, Japan, Glenn Dale from Glenn Dale, Maryland, and Rutherfordiana from East Ruther- ford, New Jersey; from the person who originated the group, such as Sander, Gable, Koster, Dawson, and Wada; or if they are hybrids from certain species, such as Indica, Kaempferi, and Mollis. Other important considerations in- volved in classifying azaleas are foliage (deciduous or evergreen) and season of bloom. The flowers may be single, semi- double, hose-in-hose, or they may be large or small. Certain general character- istics involved will be mentioned under the more important classes listed below. Ghent azaleas. Several deciduous species of azaleas have been used to pro- duce Ghent azaleas. These include Rho- dodendron calendulaceum, R. flavum (luteum), R. nudiflorum, and R. visco- sum. The group name has been latinized as Rhododendron gandavense. This group of deciduous azaleas blooms later than the Indian azaleas. Their bright yel- low-to-orange color and their foliage, which takes on fall coloring, make the Ghent an excellent selection in areas where winters are cold. Popular Ghent azaleas include Adrian, Altaclerense, Crimson King, Hollandia, Irene Koster, and many others. Indian azaleas. These azaleas are derived from Rhododendron simsi, R. indicum, R. mucronatum (ledi folium) , R. scabrum, and R. pulchrum. As a rule these varieties are evergreen. They are somewhat tender to frost and often flower early. Within the general group certain varieties are sometimes grouped accord- ing to place of origin, as the Belgian Indicas. Similarly, the Indian azaleas grown in the southern states may be grouped separately. The amateur grower, however, will probably think mostly in terms of plants and varieties that have been forced for early bloom or of varie- ties known to do especially well in the garden as contrasted to pot culture. Almost all beginners will become ac- quainted with such Indian azaleas as Albert Elizabeth (Albert and Elizabeth), Fred Sanders, Paul Schame, Pride of Mobile, Simon Mardner, and Vervaen- eana. Table 9 lists some of the many kinds. The Belgian Indicas usually force well, while the straight Indicas do not. R. simsi hybrids make up most of the Belgian Indicas. Some growers believe they should be grafted for vigor. Kaempferi azaleas. The Kaempferi azaleas in the trade have been supplied by Rhododendron obtusum kaempferi and certain crosses with R. indicum. The varieties are usually less popular than the Indicas, yet the beginner may find some worth growing, such as Alice (orange), Carmen (rose red), Garden Beauty (soft pink), Juliana (deep pink), Kathleen (rosy red) , Louise (soft pink) , and Nora (orange red). Their color range is wide. Kurume azaleas. This popular group of evergreen azaleas was derived from Rhododendron obtusum var. amoe- num, and in the trade is closely related to the Kaempferi and Sander hybrids. The flowers of many Kurumes run smaller than those of the Indian azaleas. The plants are compact and hardy. In most cases they are dwarf, this character- istic making them suitable for massing or grouping. The leaves are usually small. Thousands of Kurume azaleas were [28] brought to California in 1915 for the Panama Pacific Exposition in San Fran- cisco. Originally many of the varieties had Japanese names, some of which have now been changed to English names, as Azuma Kagami (Pink Pearl), Howo (Apple Blossom), Kirin (Daybreak), Kurenoyuki (Snowflake), and Otome (Maidens Blush). Other Kurume varie- ties are sometimes found in lists, as indi- cated in table 10. Christmas Cheer, Coral Bells, Hinodegiri, and Snowbird are popular Kurume varieties. While the plants and flowers are less spectacular individually than the Indicas and several other kinds, they do have an important place in shady gardens where mass plant- ing is needed to give color. They will also stand more cold than the Indicas and other tender kinds. Mollis azaleas. Early breeders used Rhododendron molle, R. japonicum, and R. kosterianum to develop the varieties in this group. Some fanciers refer to the Molle-Ghent Alliance, because they are all deciduous and have bright colors. Some special hybrids may be segregated under a separate name, such as the names developed by M. Koster and Sons of Boskoop, Netherlands. P. M. Koster also worked with the Kaempferi azaleas. The Mixtum azaleas may be listed separately as a double Mollis. Beginners will rarely be interested in making such fine distinc- tions, but will be interested in varieties like Adelaid (orange), Afterglow (pink), Anthony Koster (rosy red), Elizabeth (claret red), Kosters Orange (orange), Peach Blossom (delicate peach), Pink Beauty (pink), and Prince Albert (salmon rose). It will be noted the colors run to orange, pink, rosy red, rich yellow, salmon rose, or red. Hardi- ness and the later flowering season for these varieties are important considera- tions. Sander hybrids. Hybrids in this group come from Rhododendron obtu- sum and certain Indian azaleas of R. simsi derivation. Charles Sander, work- ing at the Arnold Arboretum about 1886, did the pioneer work. His name is ap- plied to the hybrid group. Almost all fanciers are familiar with Hexe (crimson red), but there are many others, such as Hebe (white striped), Rose Queen (deep rose), Venus ( cerise), and Vivid (scar- let). The Sander varieties are often known as Baby Indicas because of their suitability for small-pot culture and forc- ing. Exbury hybrids. The hybrids in this group were developed by Lionel de Roth- schild of Exbury, England, who started with the Knaphill strain of Anthony Waterer of Woking, Surrey, England. After undergoing several years of hybrid- izing and selection this fine strain of hardy deciduous azaleas became avail- able. The Exbury hybrids bloom about two weeks later than the Mollis varieties, and the flowers (up to 4 inches in diam- eter) are carried in large trusses. The colors range from white to pastels, fiery reds, oranges, and deep yellows. Some of the varieties in this group are being sold on the Pacific Coast, as listed in table 11. Gable hybrids. These hybrids are named after Joseph Gable of Stewarts- town, Pennsylvania. They bloom through April and May, and of course are appre- ciated where a hardy deciduous azalea must be selected to stand the cold. Varie- ties in this group include Elizabeth Gable (late rose pink), Louise Gable (double salmon pink) , Rose Greenly ( white hose- in-hose), and Purple Splendor (purple- red fringed hose-in-hose). Glenn Dale hybrids. B. Y. Morri- son, working at Glenn Dale, Maryland, developed these deciduous hybrids which bloom mostly from April through May. Some bloom profusely and under Cali- fornia conditions the blooming period can be extended over many months by making a wide choice in varieties. In this group varieties include Carmel, Copper- man, Crinoline, Fantasy, Fashion. Morn- [29] ing Star. Pied Piper. Serenade. Sterling, and several others occasionally listed on the West Coast. Rutherfordiana hybrids. The hy- brids in this group were developed by L. C. Bobbink. of Bobbink and Atkins. East Rutherford. New Jersey, who did some of his work about 1925. Some of the patented azaleas in this group are said to have been developed bv crossing Rhododendron indicum and the Omara- ski variety of R. pulchrum; hence the similarity to some of the Indicas. Pink Pearl I Azuma Kagami). one of the Ku- rumes. is reported to have been used in some of the crosses. The plants are ever- green, and the flowers have pure colors that range from white to deep carmine. They include singles, semi-doubles, and doubles. In California the blooming sea- son starts about February and extends into April. Like some of the Indicas. the Rutherfordianas need a temperature of about 15° F to escape winter damage. W hen grown outdoors in a warm climate they thrive in a shady or semishady loca- tion. Miscellaneous hybrids. The Peri- cat. ^ uyk. and W ada hybrids are valued for their spring bloom, coming mostly in April and May (table 8) . In California the Dawson hybrids flower in March and April. The Chugai hybrids, derived from Rhododendron indicum, bloom from April on. Their odd names, such as Row- Getsu. Gun-Rei. and Gun Bi. may be found occasionally in azalea lists. The flowering season extends into May and June. Albicans has also given rise to a few named varieties, such as Blush Beauty and Sheba, which have R. molle and R. oecidentale parentage. Here again, hardiness is a prime factor to consider when selecting this group. SUPPLEMENTARY REFERENCES American Rhododendron Society 1945- Rhododendron Yearbook. Binfords and Morts. Graphic Arts Building. Portland, Oregon. 1949. Arboretum Foundation 1946. Handbook of rhododendrons. 198 pages. University of Washington Arboretum Foundation, Washington Park. Seattle, Washington. Bowers, C. G. 1954. Winter-hardy azaleas and rhododendrons: a brief account of these plants and their culture in zero climates of the American East. 112 pages. Massachusetts Horticultural Society, Boston, Massachusetts. Dams. B. A. 1947. Azaleas and camellias for the garden. 99 pages. Hope Haven Gardens, Meridian. Mississippi. 1950. Azaleas, camellias, gardenias. 112 pages. Hope Haven Gardens. Meridian, Mississippi. Hi me. H. H. 1953. Azaleas and camellias. 93 pages. The Macmillan Company. New \ork City, N. Y. 1954. Azaleas, kinds and culture. 199 pages. The Macmillan Company. New York City, N, Y. Hutchinson, J.. A. Rehder, and H. T. Togg 1930. The species of rhododendron. 861 pages. The Rhododendron Society, London, England, and Edinburgh, Scotland. Kjncdon-Ward, F. 1950. Rhododendrons. 128 pages. Farrar, Straus. New York City, N. ^ . Roym. Horticultural Society (London) 1953. Rhododendron yearbook, 1952. after 1953. Rhododendron and camellia yearbook. Latest edition 1955, published 1954. Stoi temyer, \ . T. L941. Propagation of hybrid azaleas by means of greenwood cuttings in outdoor frames. National Horticultural Magazine, Henning, Minnesota, Vol. 20, page 181. S rREET, F. L954. Hardy rhododendrons. 192 pages. Van Nostrand, 250 1th \\e.. New York City, N. Y. [30] Table 1 — SOME COMMON NAMES APPLIED TO RHODODENDRON SPECIES Common name of species Amberbloom . . Apricotbell Ashrobe Augustine Bigleaf Bloodbloom. . . Bluet Bodinier Burmaflame . . . Cinnabar Cloudland Corrietree Falconer Fleeceleaf Fortunes Fringed Globe Goldmat Grierson Griffith Honeybell Houlston Huntingcoat. . . Madden Mandarin Mayflower Moraine Moupin Oleander Oread Pemako Royalalp Royalblood Saffronleaf Sweetshell Thomson Tibetblood Tree Trumpetmantle Twincolor Whiteshield. . . . Wight Williams Winter Woodlandglory Yunnan Rhododendron species R. flavidum R. concatenans R. tephropeplum R. augustini R. calophytum R. didymum R. intricatum R. bodinieri R. sperabile R. cinnabarinum R. impeditum R . fictolacteum R. falconeri R. chaetomallum R. fortunei R. ciliatum R. orbicular e R. chrysanthum R. griersonianum R. griffithianum R. campylocarpum R. houlstoni R. venator R. maddeni R. discolor R. racemosum R. scintillans R. moupinense R. neriiflorum R. oreotrephes R. pemakoense R. russatum R. haematodes R. eximium R. decorum R. thomsoni R. sanguineum R. arboreum R. repens R. dichroanthum R. leucaspis R. wighti R. williamsianum R. praecox (hybrid, ciliatum X dauricum) R. euchaites R. yunnanense [31] o z 5 CO Q LU CO 3 Q z < I- Ul < Q. o a. u. O Q. 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P o M too ed co co cd P ed > a ^ l-i CO O .5 Ct, co w ed < Ph # P ed o > # * CD a a ed X O P3 CD >* * * * a 41 "bo w a o bo o3 5 CO [38] Table A — SELECTED LIST OF DWARF RHODODENDRONS Variety Flowers and habit Season Adrastia deep pink ; bell-shaped Perisan rose ; 3 to 4 feet clear blue fine blue ; compact to 3 feet light blue ; to 3 feet cream with yellow flare ; compact pink ; to 4 feet white with chocolate anthers pinkish white ; to 3 feet coral pink ; low, spreading deep red ; spreading to 3 feet dark pink , spreading ; one of the best red ; bell-shaped ; to 18 inches deep red ; prostrate cerise scarlet; to 4 feet pink to creamy yellow; cupped; to 2 l / 2 feet apple-blossom pink ; shrubby to 3 feet blood red ; low, for rock garden lavender blue ; low and twiggy rosy purple and open rose pink ; compact ; fine dwarf Apr. mid-Apr. May mid-Apr. early Apr. late Mar. May mid-Mar. early Apr. Apr. -May late Apr. late May early Apr. May early May mid-Apr. early Apr. mid-June late Apr. early Mar. Arthur J. Ivens Blue Bird Blue Diamond Blue Tit Bo-Peep Bowbells Bric-a-Brac (new) .... Cilpinense Corona Elizabeth Jock Little Ben Little Joe May Day Moonstone Racil Red Cap Russautini Tessa [39] Table 5 — SOME HINTS ON COLOR SELECTIONS Color Tall growing Medium height Low growing prevailing (6 feet or more) (4-6 feet) (3-4 feet or less) White Albatross Loders White Bric-a-Brac Beauty of Little worth Cilpinense Loderi var. King George Sappho White Swan Yellow, Yellow Hammer Goldfort Bo-Peep cream, or King cup Souvenir W. C. Slocock apricot Mrs. Betty Robertson Unique Fabia group Blue, A. Bedford Blue Peter Augfast lavender, Purple Spendour Blue Bird or purple Blue Diamond Blue Tit Russautini Pink Alice Azor Corona Countess of Derby Betty Wormald Racil Faggetters Favorite Lady Bessborough Tessa Loderi var. Venus var. Roberte Mother of Pearl Lady Rosebery Pink Pearl Mrs. C. B. Van Nes Mrs. Furnival Mrs. G. W. Leak Naomi group Royal Flush Vanessa group Red, rose red, Cynthia Bonfire Arthur Osborn or crimson Jean Mary Montagu Britannia Elizabeth C. B. Van Nes Little Ben David Little Joe Earl of Athlone May Day Gills Crimson Red Cap Lady Bligh Mars Tally Ho Vulcan [40] Table 6 — SOME AZALEA COMMON NAMES AND RHODODENDRON SPECIES INVOLVED Common name Albicans Arnold Autumnleaf Cascade Chinese Coast Flame Fringed Indica. Ghent Hiryu Indian Indica Japanese Koster Kurume Lovely Luchu Mortier Oconee Orange flame. . . Piedmont Pinkshell Pinxterbloom . . . Plumleaf Pontiac Rose Roseshell Royal Sander Smooth Snow Sunbeam Swamp Sweet Torch Western White White Piedmont Yodogawa Rhododendron species R R R R R R R R R R R R R R R R R R R, R. R. R. R. R. R. R. R. R. R. R. R. R. R. R. R. R. R. R. R. . molle X R. occidentale . arnoldianum (A. obtusa amoena X A. obtusa kaempferi) . semibarbatum . albiflorum . molle . atlanticum . calendulaceum . indicum laciniatum . gandavense (group of hybrids between R. flavum and hybrid Mortieri) . obtusum . simsi and hybrids . indicum . japonicum . kosterianum (hybrid between R. japonicum and R. molle) . obtusum japonicum . pulchrum . scabrum (sublanceolatum) . calendulaceum X R. nudijlorum . speciosum . calendulaceum aurantium . canescens . vaseyi : nudijlorum . prunifolium , jlavum (luteum) . reticulatum , roseum schlippenbachi sanderi (R. obtusum X R. simsi) canescens glabrum mucronatum (R. ledifolium) altaclerense (R. catawbiense X R. ponticum X R. arbor cum) (1826) viscosum arborescens obtusum kaempferi occidentale obtusum album canescens candidum yedoense [41] rs co O 3 "3 a T3 co CO 3 3 O O 3 3 *3 *3 C3 O a> CO CO CO CO 3 3 a; 3 3 3 3 O O . 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S3 32 o3 CD 43 CO — a P-t co 03 CD 13 S3 o3 o3 o3 bC O O "? s u eg « O =3 R a u a ta a ? | a o a a o a a CO o a © 5 a e a a. CD CO a CO © y. CO CO a "S? co CO a © as 03 0:^(^030303 03 03 Q3Q3 03 ^v 03 03 03 03 [42] Table 8 — SOME AZALEA HYBRID GROUPS OF POPULAR INTEREST Hybrid or group Albicans Altaclerense Arnold hybrids Belgian hybrids Chugai hybrids Dawson hybrids Exbury hybrids Gable hybrids Ghent hybrids Glenn Dale hybrids Indian hybrids Kaempf eri hybrids Koster hybrids Kurume hybrids Molle- Ghent Alliance Pericat hybrids Rutherf ordiana Sander hybrids (Baby Indicas) Vuyk hybrids Wada hybrids Season of bloom Foliage May deciduous May deciduous May-June evergreen Nov. -May evergreen May evergreen Mar-Apr. Apr.- May deciduous Apr.- May evergreen Apr. -June deciduous Apr.-May deciduous Dec-Mar. evergreen Apr.-May evergreen May- June deciduous Feb.-Apr. evergreen Apr. -June evergreen Feb.-May Mar.-Apr. evergreen Feb.-Apr. evergreen Apr.-May Apr.-May evergreen [43] < UJ < N < Z < a z a. < Q. o o. UJ o 03 p bo o3 3 ? 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H Eh CO Xi p a o 'G Eh xf p a §1 .2 eh PL, v^ co co , fH " *! o *S * P 1 P CO CO o I JS-g 2 > P fH CO CO iH fH CO «W Eh Eh > > CO XI eo P CO co P CO CO > fH CO > CO CD CO o P4 CO p CO CD C Si CO CO > 43 »H O co .2 > > CO bo P CO fH O P CO > a CO [45] Table 10 — SOME POPULAR KURUME AZALEAS* Variety Color and type of flower Apple Blossom (Howo) Avalanche apple-blossom pink ; single pure white bright salmon; single carmine rose ; medium double bright red ; double ; early coral pink ; small double ; early ; boxwood-like folia' e mauve ; double deep rose shading silver lavender double with high center ruby red ; midseason light lavender ; late blush pink mauve ; hardy light pink ; double ; tall ; midseason salmon pink ; double ; midseason white rose pink striped carmine medium double ; baby pink Bridesmaid China Sea Christmas Cheer Coral Bells Daphne Daybreak (Kirin) Double Mauve Hinodegiri Lavender Queen Maidens Blush (Otome) Mauve Beauty Pink Pearl (Azuma Kagami) . . . Salmon Beauty Snowflake (Kurenoyuki) Sunstar Sweetheart * Other varieties sometimes listed include: Early Dawn, Firebird, Oimatsu, Salmon King, Salmon Queen, and White Swan. Few nurseries list many Kurume azaleas. Table 1 1 SOME EXBURY AZALEAS A SELECTED LIST Variety Color Balzac Basilisk Berry Rose red with flame markings creamy yellow bud opens to cream with golden flare medium pink tangerine red salmon pink with yellow flare ; large deep orange orange red ; frilled rich yellow tangerine orange flame red bright orange clear deep pink large red tangerine Brazil Cecile Firefly Frills George Reynolds Ginger Hotspur A.M Knighthood Pink Delight Royal Lodge Tangiers I 46 | In our publications it is sometimes convenient to use trade names of products or equipment rather than scientific identifications. In so doing it is unavoidable in some cases that similar products which are on the market under other trade names may not be cited. 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