Fig. Rhododendron Loderii. Painted by Josephine Gundry.
Botanists, pointing to the trifling differences between Azaleas and Rhododendrons, amalgamate them. Even if we consider them as separate genera the Rhododendron is supreme, with the Azalea it is unchallengable. There are, however, shrub-lovers who have to dispense with Rhododendrons in their gardens, owing to the soil containing lime. The Azalea and Rhododendron belong to the botanical order Ericacaee, the members of which are lovers of peat. While, however, they enjoy this earth, it need not be assumed that they will not thrive in other soils. Many authorities on these shrubs would not use peat exclusively if they were making special beds, although they would gladly avail themselves of a natural peaty soil for these and other of the beautiful and fascinating Ericacaee if circumstances took them into a district where it prevailed. When making special beds they would use a good deal of fibrous loam in addition to peat; for it has been proved that this soil suits Rhododendrons if it is free from lime. From the garden point of view it is convenient to keep Azaleas and Rhododendrons separate, because, in the main, they serve distinct purposes; moreover, they are separate in most of the catalogues. The Azaleas of the mollis and sinensis sections, and their hybrids, are deciduous, and of low or medium growth. The most important Rhododendrons are evergreen, and are of almost tree-like habit in suitable soil. There are, of course, deciduous Rhododendrons, but the broad distinction will serve.
The species of Azaleas and Rhododendrons are, as a rule, of little interest to amateurs, although of great interest to botanists. The long lists of named sorts in the catalogues - the Anthony Kosters and Pink Pearls, the Glory of Boskoops and John Waterers, of nurserymen - are garden forms of hybrid origin. The garden-lover does not know whence they came, and it would be a difficult task to trace the parentage of the best modern varieties. Few species of Azalea are met with in gardens, and for all practical purposes they can be dismissed. One can hardly go so far with Rhododendrons. We have already seen that ferrugineum and hirsutum, the Alpine Roses, are grown in rock gardens. Racemosum is used for the same purpose, as well as for winter-blooming in pots. Ponticum is planted extensively in woods. Campylocarpum, catawbiense and caucasicum are sometimes met with. But in nine gardens out of ten it is the hybrid offspring of some of these and other species which are grown. The principal species which have been used as parents for Rhododendrons are ponticum, catawbiense, ar-boreum, maximum, caucasicum and purpureum. With respect to Azaleas, what are known as Ghent Azaleas sprang from the species pontica (not Rhododendron ponticum, but the plant known to botanists as Rhododendron flavum, a yellow-flowered deciduous shrub, a native of the Caucasus), calendulaceum (occidentale), nudiflorum and viscosum, all hardy North American species. Although the Ghent Azaleas are hardy they are mostly used for pot culture and are grown in enormous quantities by Belgian florists for winter bloom under glass. Azalea mollis (Rhododendron sinense of botanists) is known to have been crossed with pontica, and has probably been crossed with others. Several hybrid sections are offered by nurserymen and the exact parentage is doubtful.
Coming to the purely gardening aspect of the subject, we have seen in previous chapters that Rhododendrons and Azaleas are magnificent shrubs for lawn beds, and also for large borders. The coloured plates show with what remarkable effect they can be grouped, forming brilliant colour masses. We have also considered propagation and other cultural matters. It may be well to make clear that when peat is referred to the peat of a stagnant bog is not meant, but sweet sandy peat. Rhododendrons love cool but not waterlogged spots. A humid climate suits them better than a dry one, witness the grand plants in the famous Cornish gardens. But Rhododendrons are at home in Surrey, particularly on the upland sandy peats around Bagshot and Woking. When sites are prepared for them the imported soil should be put in mounds above the ground level, not in pits made by carting the native soil away. In the latter ease lime, if present, would eventually work its way into the bed some time in the future. If the soil is light and sandy leaf mould may be added with advantage. Rhododendrons have great tenacity of life, and when suited by soil and climate are the easiest of plants to grow. Lime has a singular toxic effect on them the exact nature of which is not known. Cunningham's White, will, however, thrive on limestone. The following are splendid hardy Rhododendrons in the various colours: Bicolor: Sappho, Mrs. A. Walter, Francis B. Hayes and Lady C. Walsh. Blush or pale pink: Pink Pearl, Go mer Waterer and Mrs. E. C. Stirling. Deep pink and rose: Lady C. Mitford, Kate Waterer, Strategist and Lord Palmer-ston. Red: Cynthia, John Waterer, John Walter, Doncaster. Purple or plum: Baron Schroder, Melton and Old Port. White: The Queen, Mrs. J. Clutton and Memoir. Where only one of each colour is required the first named may be chosen. The following newer varieties are beautiful, but it may be expected that the cost of them will be higher; Alice, a giant of deeper colour than Pink Pearl; Princess Juliana, blush; Gill's Goliath, blush with deeper pink edge; and Cornubia (Thomsoni + Shilsoni) bell-shape, dense blood red; some good hardy deciduous Azaleas are described in Chapters 9. and 26. The flower-heads of Rhododendrons should be pinched off short when they fade, using finger and thumb carefully so that the growing bud at the base is not broken off. This removal of fading flowers prevents seed pods forming and the plants bloom the better for it the following year. We have often been struck with the way in which old Rhododendrons that were getting bare below have broken up green, fresh and strong when headed at midwinter to hard wood as thick as a man's leg. This should interest and encourage those who have gawky plants. Growth will break from brown barky wood that shows no sign of buds. A dressing of leaf mould or decayed manure is spread over the roots. For other references to Azaleas and Rhododendrons see Section A. on modem shrubs, also Chapters 3., 7., 11. (propagation) 13. (pruning), 14., 19. (rock subjects), 25. and 26. (forcing).