The author, a partner in Western Hills Nursery, continues his discussion of colored and variegated plants with a survey of those with gray and silver leaves.
In the latter part of the last century, Gertrude Jekyll created her famous colored foliage borders and they caused a virtual revolution in English gardening. In one particularly notable example, a variety of blue, blue-green and silvery plants were used in one direction from a central viewing point and yellow and golden plants in the other. Visitors looked one way at a cool, bluish world, then had only to turn around to find a warm, golden one. Since then, many English gardeners and some Americans have attempted borders in limited color schemes; the white garden at Sissinghurst is undoubtedly the most famous example in this genre. Gardens of this kind are tightly enclosed spaces where the visitor is transported into another world. It is a marvelously harmonious and thematic world, very different from the large natural vistas of the great landscape gardens and, most especially, excitingly different from the dark and unrelieved masses of laurels, yews and rhododendrons that had come to be the rule in mid-Victorian gardens. This new form was a careful, detailed and painstaking garden art; the plants were not only carefully placed but also carefully controlled and subordinated to a final, overall effect, whose aim was to dazzle the eye with color or seduce the mind with harmony. Plants had, indeed, become garden material.
I am impressed by these efforts and not insensitive to their results. Nevertheless, I find the exercise as a whole to be too much like interior decoration for my taste. The totality overwhelms the viewer but much of the individuality of the plants comes to be lost in the process as they are tucked here and there and trimmed, trained and staked always with a masterful overall effect in mind. I prefer an arrangement that allows the full display of the plants themselves in all their natural, and preferably unpruned, grace. Also, I think we should, wherever possible, pay attention to the places of origin of our plants. At the same time, I should like to consider all aspects of plant associations, including leaf color, to enhance the general surroundings wherever this can be done consistently with my other aims. There is no doubt a contradiction here, and it is, in fact, one of the banes of my life; it is also a great joy since it makes of the garden an unsolved problem that must be attacked repeatedly with ever renewed vigor. In this scheme of things, what is foliage color? I suppose I should have to say that it is just one of many aspects of plants we can consider and can use freely to create a place where both we and the plants are at home.
Most trees and shrubs with white, silvery or blue leaves differ from the plants discussed in the previous article (Spring, 1982) in that their coloration can in no way be considered abnormal. A blue, white or gray cast to foliage is usually a means of reflecting sunlight and helping plants to survive drought, heat and other adverse conditions; in other words, they are an adaptation to the environment. Most of our store of such plants is not, therefore, the result of vegetative propagation and the nurturing of a few seedlings; unlike most red or yellow foliage plants, these come true from seed — with minor variations. It follows that the best place to look for an increase in such color forms for horticulture is in nature and not in nursery catalogues.
The terms gray, gray-green, blue, blue-green, white and silvery have been used loosely and inaccurately (sometimes indeed synonymously) in a bewildering way. I have seen plants as dissimilar as Acacia baileyana and Salvia leucophylla described as gray. Such words as incanus, glaucus and glaucophyllus have a more scientific sound but are often also used loosely. Since I think this is a matter of some importance to gardeners, I shall try to use these words with greater accuracy.
Evergreen Trees and Shrubs
For gardens where they are hardy and appropriate, the eucalypts offer a very large number of blue and gray trees and large shrubs. As I have said elsewhere, the mass planting of these trees in California has been a disservice to them. Where they are used as specimens, as in the gardens of southwestern Ireland, or as temporary foliage plants, as in England, and where they are not otherwise present in the landscape, their true worth as garden plants can be appreciated. The Blue Mountains west of Sydney, Australia, are named for the many eucalypts with blue foliage found there. The traveler finds himself in a soft-colored dreamlike world, far removed from the rigid shapes and the deep green of northern conifer forests. Perhaps the most stately of all the trees that comprise this great spectacle is Eucalyptus oreades, the Blue Mountains ash, which has a tall white trunk supporting a mass of interlacing white limbs and an umbrageous head of very blue foliage. In spring, this great tree is alight with red new growth; it is a true paradise garden plant. Equally beautiful is Eucalyptus mannifera subsp. maculosa (syn. E. maculosa) which has blue foliage and the whitest of white trunks. Majestic specimens of it dominate the Canberra Botanic Garden. Both Eucalyptus oreades and E. mannifera var. maculosa are fairly hardy, at least to 15° F.
The most common of the smaller eucalypts grown for their light blue foliage are Eucalyptus pulverulenta and E. perriniana, many acres of which are grown in California for the florist’s trade. There are several others, however, that may have characters more suitable for our gardens. E. melanophloia, for example, is a medium-sized tree with a black trunk of the iron-bark type and a head of blue leaves. The silver peppermints, E. risdonii and E. glaucescens are smaller, very glaucous and very picturesque trees. All of these are among the hardier eucalypts. Even more spectacular, although less hardy, are E. kruseana and the southern cross mallee, E. crucis. The first of these is perhaps the most astonishingly blue of all plants and the second is a very light silvery gray.
Three very blue or blue-gray shrubby eucalypts grown for their large red flowers as well as their glaucous foliage are Eucalyptus macrocarpa, E. rhodantha and E. pyriformis. Of these, E. macrocarpa has not only the largest flowers but also the palest blue-gray foliage. It makes a bush five feet high and up to ten feet wide and its fiery red flowers are five inches across. Unfortunately, it is not very hardy and should not be attempted in gardens with more than six or seven degrees of frost.
Like many conifers, eucalypts have both juvenile and adult Foliage and the former is often glaucous or silvery even when the adult leaves are not. Since, like willows, these trees can be pollarded or cut to the ground and will respond with long annual growths, and since these will all bear juvenile leaves, it is possible by this means to create large and interesting foliage masses. To my mind one of the best to be used in this way is Eucalyptus gunnii, which has unusually graceful juvenile foliage. Because this is one of the hardiest of eucalypts, it is often used in English gardens and its handsome blue leaves displayed in front of dark yew hedges. It is also effective planted with other silver and blue shrubs.
The number of acacias with blue or silvery foliage is so great that I can include here only the most striking of those I know or have seen. The largest of all is the well-known silver wattle, Acacia dealbata, which, grown as a specimen, will make a stately mass of feathery, silvery-gray foliage fifty feet or more high. A. dealbata is one of the hardiest of acacias and is one of those, like A. decurrens, that puts on an overwhelming show of light yellow flowers in late winter and very early spring. Half the size is A. baileyana, which can be trained to a single trunk as a small tree or grown with many trunks as a very large bush. Although common, I find the Bailey acacia one of the most satisfyingly blue of all woody plants. This is particularly true of A. baileyana ‘Purpurea’ which has lavender new growth and bluer foliage as well. Not only is the foliage of this acacia distinctly blue, but it has a remarkably silvery sheen from the white undersides of the leaves, which flash brilliantly in some lights. Of nearly the same size, but with large willow-shaped phyllodes is A. saligna (syn. A. cyanophylla), which has a pleasing blue-green hue overall, and deep yellow flowers.
Smaller than these, but still a very large shrub is the outstanding, very light blue acacia, Acacia podalyriifolia, which has gracefully arching branches and rather large, triangular, stem-clasping phyllodes. Unfortunately, this plant is not very hardy and will show damage at temperatures below 25° F. Its pale yellow flowers, for which the foliage is a perfect foil, appear in mid-winter and remain until spring. It is in every way a very satisfying plant for warm gardens.
Acacia pendula is for many years a graceful weeping shrub, although it slowly grows into a small and finally a large tree. Plants of it in California, fortunately, have silver-gray phyllodes. Acacia pendula is described by Lord, in Trees and Shrubs for Australian Gardens, as green, and all those I saw in Australia were green. A. pendula is hardy to about 18° F., and all the plants I know of survived the terrible winter of 1972 without damage.
In addition to these sizable shrubs and trees, there are many smaller acacias with gray or blue foliage. One of the best of these is Acacia pulchella, a very blue and very delicate shrub to five feet or so from the area around Perth in Western Australia. It is not hardy, and died here in 1972.
Some plants that are described as silvery are merely white. The term is more aptly used to describe those plants with white undersides to their leaves and that glitter in certain lights when moved by a breeze. However, the term best describes foliage that has a gray or white satiny sheen from a covering of silky hairs or shiny scales. Perhaps the most renowned of the plants with foliage of this kind is the silver tree, Leucadendron argenteum, whose leaves are bright green but so covered with long, soft silky hairs that they glisten like silver in the sun. This small South African tree is hardy down to about 24° F., but it is not easy to grow even where temperatures will allow; in a wet winter trees are apt to die almost overnight from collar rot. Banksia marginata, the silver banksia, is an Australian tree of about the same size. It is not nearly as effective as the silver tree since its scalloped leaves have white silky hairs only on their under-surfaces. It is nevertheless a beautiful tree with a distinctly silvery presence. An easy plant to grow, it is not particularly subject to root rot and is far hardier than Leucadendron argenteum.
An overwhelming majority of the shrubs with silvery or blue leaves come from the Mediterranean climate areas of the world. Gardeners who like to experiment and whose winters are on the mild side will find the Australian and, to a lesser extent, the South African floras rich with such plants; only a few of them have been introduced into the nursery trade. In addition to the smaller, glaucous acacias, there are at least a dozen Australian genera that have shrubs with startlingly white or silvery or blue leaves. Very striking in the Australian bush, for example are lamb’s tails (Lachnostachys spp.) which have white woolly leaves and densely woolly inflorescences in spikes. Perhaps the most glistening, pure white bush of all is a native of the south coast of Australia, Calocephalus brownii, a mounding shrub sometimes found in California nurseries. Also occasionally available is Melaleuca incana, a very beautiful, gently weeping, soft gray bush to six feet or so that blooms with masses of creamy yellow flowers. A very blue leaved grevillea is Grevillea lavandulacea ‘Tanunda’, a low spreading shrub of reasonable hardiness with large, showy pink flowers. Some banksias, such as Banksia menziesii, have beautiful glaucus leaves and new growth covered with golden indumentum. There are many, many more white-leaved eremophilas and gray-leaved cassias from the inland, for example, and such favorite plants in Australia as the old man salt bush, Atriplex nummularia.
From South Africa there is a striking blue-leaved heather, Erica bauera, which has an elegant, thin habit and very large pink or white flowers. There are also several proteaceous shrubs, other than the silver tree, with blue or gray foliage, and all the euryops are gray, woolly, low shrubs with yellow daisies. Special mention should be made of an extraordinary African shrub, Helichrysum splendidum, a very effective, nearly pure white plant that has a wide distribution from the Ethiopian mountains all the way to the Cape. This very ghostly shrub grows to about four feet or so, and as wide; it is well furnished with narrow, revolute white woolly leaves. Unlike most of the shrubs mentioned above, this one is hardy throughout the Pacific Coast. It is beautiful, and its only drawback is a certain gawkiness that is easily cured with a minimum of pruning.
The most famous silver and gray shrubs of all are the santolinas, lavenders, artemisias and similar plants from the shores of the Mediterranean. Many of these I have already described (Pacific Horticulture, Summer 1980). They will also receive further attention in these pages from Christine Rosmini, whose survey of low white and gray shrubs from mountainous areas, will supplement this brief account of the garden-worthy glaucous plants of the world.
A fair number of superb shrubs with blue, gray or white leaves can also be found in the California flora. One of the most outstanding of all these is Arctostaphylos viscida, which catches the eye of all travelers in the Sierra Nevada foothills with its very light gray, almost white leaves and smooth red limbs. Unfortunately this is one of the most difficult of manzanitas to grow away from its native habitat. A good substitute for gardens in the Coast Ranges is Arctostaphylos silvicola, which has a dark red trunk and gray leaves that are not nearly so white as those of its Sierra relative. Leaf color varies considerably among plants of some Arctostaphylos species, and some very blue plants of A. glauca and very pale gray bushes of A. manzanita, among others, are to be found. If collections were made with these qualities in mind, the result would be handsome additions to our stock of colored foliage shrubs.
The California atriplexes are all gray shrubs, but, although they are picturesque in their native habitat, only one, Atriplex hymenelytra, the desert holly, can be considered beautiful and it is next to impossible to grow in the coast ranges. Atriplex lentiformis var. breweri is a plant that, while far from beautiful, can be used to handsome effect among other colored foliage shrubs. It makes a mound of silvery-gray leaves eight feet high and more across — large for a salt-bush. This plant is found in the coastal scrub and is easy to grow throughout most of California, and, unlike A. lentiformis var. lentiformis, it is basically evergreen. Two native artemisias are of rather similar value. Sagebrush, Artemisia tridentata, makes a silvery bush sometimes fifteen feet high. At its best it is wild-looking and handsome. In summer A. californica, from the coast, makes a very beautiful, light blue-gray, low shrub with soft, ferny leaves. In winter it looks something like a wet dog and is best pruned back to the base.
Some California salvias also make excellent mounding gray and white bushes. The whitest of all, although its flowers are not very effective, is Salvia Ieucophylla, a very serviceable bush, easy to grow almost everywhere. Salvia clevelandii is more gray but has, in its best forms, beautiful lavender-blue flowers arranged in several heads along the flower stalk. The entire shrub is one of the most delightfully fragrant of all salvias. A hybrid between S. Ieucophylla and S. clevelandii is S. ‘Allen Chickering’, an attractive plant which is often sold in nurseries as S. clevelandii.
Isomeris arborea and Dendromecon rigida subsp. harfordii are both rangy shrubs that have excellent glaucous leaves and beautiful yellow flowers; both of these can be effective planted in the right places. The dendromecon can grow far too tall and straggly; then it is best cut all the way to the ground. Perhaps the most important of all additions to our list from the California flora are the lovely blue mahonias from the southern part of their range. These are excellent, hard-leaved shrubs providing permanent furnishing for gardens, and they accord well with barberries, hollies, boxwoods and manzanitas. When grown from seed Mahonia amplectans is quite variable, but selected blue seedlings are very attractive; they make low bushes, seldom as much as five feet high. M. haematocarpa and M. higginsiae are taller bushes with smaller, very spiny, blue-gray leaves. Mahonia nevinii is still larger and may grow to twelve feet. It can also be very blue and is the showiest of all in fruit, its brilliant red berries hanging in clusters like currants. All of these shrubs are adaptable plants and will grow in northern as well as southern California; they will also thrive in the Central Valley given some shade.
In addition to trees and shrubs with silvery foliage that come from areas with a long dry season, there is a sprinkling of such plants from regions with year around rainfall. Most of these are deciduous, but a striking evergreen exception is Elaeagnus macrophylla from Korea and Japan. This plant has larger leaves than the better known E. pungens, and they are particularly effective in spring when the entire leaf surface, top and bottom, is covered with glistening silvery scales. As the season progresses, the upper-sides of the leaves become green, but the lower scales remain and continue to give the shrub an over-all silvery appearance. E. macrophylla is a large shrub to twelve feet and as much across. It is hardy throughout the Pacific Coast and has the virtue of blooming very late, in October and November, with small but delightfully fragrant flowers. This shrub is not now available in the trade, but E. x ebbingei (a hybrid of E. macrophylla and E. pungens) has now become common in nursery lists. This is also a beautiful shrub, although its leaves are not so handsome as those of its large-leaved parent.
Deciduous Trees and Shrubs
To my mind, the most beautiful of all silvery deciduous trees is a willow — Salix alba argentea (S. alba sericea). For country places with low lying areas, this is one of the best of
all trees to plant. Unlike many silvery or blue-foliaged trees, the form and color of this tree accord perfectly with our native vegetation. Bean praises the “intense silvery hue of its leaves, conspicuous in their shining whiteness for long distances.”
The white-leaved pears are much smaller trees, excellent for small gardens. Pyrus nivalis is a European tree with woolly white leaves and masses of white flowers in spring, although the upper surfaces of the leaves change to green in summer. Pyrus salicifolia from the Caucasus, parts of Turkey and Iran, has silvery, willow-like leaves and a naturally pendulous habit; especially weeping forms have been propagated and sold as P. salicifolia ‘Pendula’. This tree provides more than beautiful foliage; it is also one of the most beautiful of spring-flowering trees, when its masses of white flowers set in white wool unfold at the same time as the silvery new growth. Also an effective tree is Pyrus x canescans, probably a hybrid between P. salicifolia and P. nivalis.
Relatively unknown, but an extremely beautiful tree for its foliage is Sorbus cuspidata from the Himalaya. The leaves of this tree — which are up to seven inches long by five inches wide — are completely covered with white down in spring. Although, again, the upper leaf surfaces gradually become glabrous, the tree continues to present a remarkably silvery look. The corymbs of white flowers in spring are white and woolly inside and are set in white woolly receptacles; the fruits in fall are yellow. Sorbus cuspidata is a large tree in nature but has remained under forty feet in cultivation in England; how large it will grow for us remains to be discovered. Our plant, although still small, is perfectly healthy and seems well adapted to our climate.
Some white poplars, Populus alba and P. canescens, give a silvery impression from the light coloration of their leaves with their white or gray silky undersurfaces. Populus alba ‘Pyramidalis’ (which has been known as Populus bolleana) is the most widely planted of these and is the most common silvery deciduous tree in cultivation. Compared with the trees described above, however, it is a crude plant, difficult to use in the landscape. The only way I can describe its quality is by saying that the tree is extremely fast growing and, unfortunately, looks it.
The Russian olive, Elaeagnus angustifolia, is another common but rather more handsome tree. It is not a large tree and its color is both lighter and less gray than an olive. Planted in groves or where its pale gray-green foliage shows to advantage, it can be very effective, particularly in hot-summer areas.
Perhaps the most beautiful of all silvery deciduous shrubs is also an elaeagnus, Elaeagnus commutata, a native of eastern United States. The leaves of this delightful shrub are covered both sides with silvery scales and, unlike the leaves of many others, remain so throughout the summer. The small silvery and yellow flowers in spring are not showy but are extremely fragrant. Despite its deciduous habit, this shrub is worth growing in Pacific Coast gardens. It will reach twelve feet, but is easily kept lower by pruning in the dormant season.
A close relative of elaeagnus is Hippophae rhamnoides, a tall, upright growing deciduous shrub with narrow silvery leaves and bright orange berries that persist in winter because they are unpalatable to birds. This beautiful shrub is also a very useful one, since it will tolerate over-wet soils but is nonetheless drought resistant. Its only drawback is that it is unisexual; both male and female plants are necessary for pollination.
I must mention two other deciduous shrubs that have garden value. Zenobia pulverulenta is an ericaceous shrub from the southeastern United States. It is a low shrub, only about three feet high, with beautiful gray foliage that turns to shades of pink and yellow in winter. It has hanging clusters of white flowers like a pieris, and is an excellent shrub to plant among rhododendrons to offset their rather heavy green foliage. The other is the blue arctic willow, Salix purpurea ‘Nana’, a shrub to five feet or less with small blue-gray leaves and purple stems in winter; this is a first-class shrub for low-lying areas and is beautiful at all seasons.