The allied plant known as St. David's Heath, DaboŽcia (or Menziesia) polifolia, may also be planted with advantage. This beautiful little plant looks charming in a peaty bed near the base of a rockery, but the site must not be wet. It is essentially one of the things that should be planted in some quantity. Single plants have interest, of course, and better one than none; but the planter who can make a little colony of them will enjoy them most.
Similar remarks, alike as to interest, soil, site and planting, apply to the exquisite Pernettyas, the main interest in which lies in their pretty berries. These shrubs are also admirable for the rock garden.
A shrub which likes lime as much as the Rhododendron resents it is the Cistus or Rock Rose; moreover, it is evergreen. It is the limestone garden-lover with hot, dry sites to furnish who will feel the deepest gratitude towards the Cistus. Vain is it to look towards the Ericacaee (an order, be it noted, that includes the Rhododendron as well as the Erica) when a parched southern slope on chalk has to be furnished. Wherever it can establish a foothold, be it only in a handful of soil on a limestone bank, the Cistus will thrive. The fact that its flowers only last a few hours need not repel the planter, for he will find that a long succession of bloom is produced, and more often than not when he examines the plants, throughout the summer, he will find flowers. The blossoms are as beautiful as great single white Roses, or Japanese Anemones. The species differ a good deal in habit. The nomenclature of the genus appears to be straightforward enough, but when one sees the plants in the large nurseries, it becomes apparent that great confusion exists, and a reference to Sweet's old work on Rock Roses shows that the same trouble was experienced many years ago. Salvifolius and corbariensis are sold indiscriminately; the former has a rounder leaf than the latter; both are grey-leaved, and comparatively dwarf. Still worse, cyprius, a quite different species, is sold for both the foregoing; it has a bronzy green leaf.
Fig. A Little Known But Beautiful Rock Rose. Cistus creticus. Photo by R. A. Malby.
Ladaniferus and longifolius florentinus are relatively tall. All those named have white flowers, but a form of ladaniferus, called maculatus, often sold as the type, has chocolate blotches. Crispus has purplish magenta flowers.
In poor limestone soil, on a hot dry site, none of the species is likely to grow more than three feet high, and they will not make large bushes, as they will do on better ground; it is a question, however, if they are not longer lived. Where the plants prove to be shortlived, it is prudent to put in a few cuttings annually, and they may be inserted in gritty soil in May.
A plant belonging to the same order as the Cistus, and likewise a hardy evergreen that will luxuriate on hot dry limestone soils, is the Helianthemum or Sun Rose. It is even more valuable than the Cistus, because it is lower and more spreading in habit and produces a profusion of brilliant flowers over a longer period. It is rarely out of bloom in summer, and the double forms are particularly lasting. The planter need not trouble about species here. He should get florists' named forms, such as Kitty, Primrose Dame, Pink Beauty, Fireball, Jubilee and Garibaldi.
The three best Daphnes, Blagayana, Cneorum and Mezereum, are all suitable for the rock garden. These little plants should have the special attention of the small gardener, for they are neat and compact in growth. They give, too, delicious perfume.
Fig. The Three Best Daphnes, Blagayana, Cneorum, And Mezereum Are All Suitable For The Rock Garden. Colour photo of D. Cneorum by R. A. Malby.
Azaleas of the mollis and sinensis sections and hybrids between these species are, as we have seen in previous chapters, particularly adapted for beds on lawns, or for "bays" along the front of large shrubberies; but they may also be used in the rock garden, and they will be particularly at home in peat beds at the base of a large rock bank.
The Brooms comprise species of widely varying habit, and while Cytisus scoparius and its beautiful forms Andreanus and sulphureus, C. albus, C. praecox, and C. Dallimorei are perhaps best suited for borders and beds, dwarfer and prostrate kinds like C. Ardoini, yellow; C. hirsutus, yellow; C. kewensis, cream; C. purpureus, purple, and its forms albus, versicolor and incarnatus, and C. decumbens, yellow; are admirably adapted for the rockery. The last named species is often found under the name Genista prostrata, and an early yellow form called praecox (not the same as Cytisus praecox, which is a cream-coloured hybrid growing several feet high) is offered by florists. Of the Genistas proper, hispanica and its variety nana; tinctoria and its double variety; germanica, sagittalisj and pilosa are suitable. G. tinctoria flore pleno is an excellent small yellow shrub.
Fig. The brooms comprise species of widely varying habit admirably adapted for the rockery. Cytisus praecox and C. Kewensis are here shown. Painted by G. Soper.
The mountain Avens, Dryas octopetala, with white flowers, is a good plant.
The Magnolias are in the main too bulky for ordinary rock gardens, but there is one deciduous species that produces its glorious pure white flowers in advance of the leaves, which is of slow growth and compact habit; this is stellata. The rock-gardener should seize upon it as upon a gem of purest ray.
Among the species of Rose, which are a sealed book to many people who claim a considerable knowledge of Roses - natural species, be it understood, not nurseryman's varieties of hybrid origin - there are many beautiful and interesting plants, some of which can be brought into use for the larger rock gardens, especially where there are arid banks to cover. For this purpose Wichuraiana and its garden forms are admirably adapted. Rosa arvensis, the Ayrshire Rose, is also a straggly creeper. Of upright growers, cinnamomea and its varieties; sericea, an Indian species with white flowers; spinosissima and its forms altaica (white) and lutea (yellow); the dwarf alpina and its beautiful carmine form pyrenaica; likewise pimpinellifolia and xanthina, are all interesting. These Roses might be planted on the summits of mounds, the faces of which were planted with Alpines. Their light, free, graceful growth and abundance of pretty single flowers give a delightfully pleasing and natural effect.
A few selected Spiraeas may be introduced with advantage. Decumbens (syn. procumbens) is a natural trailer with white flowers.
The Veronicas comprise species suitable alike for their flowers and their foliage. V. cupressoides is grown for its habit and foliage; it is quite cypress-like, and evergreen. V. Hectori, also an evergreen, has a pretty buff tint in the foliage in autumn and has attractive lilac flowers. Incana, repens and Teucrium are good carpeters, but these are herbaceous. Epacridea, with a buff tint in autumn, not quite hardy, pinguifolia, decumbens, and Traversii are all good.
Yuccas, such as filamentosa and gloriosa, will serve.
Fig. Two useful rock garden shrubs. Upper - Thuja dolabvata nana. Lower - Picea excelsa Remonth.
Several of the smaller Conifers may be made use of in the rock garden. Admirers of Japanese gardens will not fail to observe the way in which these evergreens are pressed into service. The smaller the garden the more cunningly are these little shrubs used to give an effect of space and distance. A proportion is carefully maintained between them and the other occupants of the garden. Picea (or Abies) clanbrasiliana, P. pumila, and its form glauca, P. pygmaea, Cupressus (or Retinospora) obtusa and its forms aurea, Crippsii, lycopodioides, and gracilis aurea, C. ericoides, C. pisifera and its form aurea, Juniperus Sabina and its forms, particularly tamariscifolia; J. hibernica compressa and Podocarpus alpinus are all well adapted for the purpose in view.
The creeping Cotoneasters, such as horizontalis and Dammeri, are admirable for rock gardens. They are close growers and have pretty berries.
Those who wish to practise Alpine gardening on poor soil, and whose means do not permit of importing better soil, should draw largely on small shrubs. They will be particularly useful in the early days of the garden, before the Alpines have become thoroughly established.