I have never felt the disgust for variegated foliage evinced by so many good gardeners, and in many cases l warmly admired it. Towards the end of summer, and before the autumnal tints begin to brighten them up, most of our shrubs and trees become very heavy in their tone of green, and we miss the contrasting shades of spring vegetation. Then the value of a silver elm or Acer negundo, the ghost tree, and of golden-leaved shrubs is apparent.
There are so many plants with colored or variegated foliage that it would be pointless to describe all or even most of them. New cultivars are continually appearing and the day will perhaps come when such sports have been found and propagated of almost every woody plant widely (and some not so widely) used in horticulture. Not everyone likes them. I have a friend, an excellent gardener, who detests them and considers them in a class with diseased plants and weeds that should be destroyed. I like them, or, I should say, I like the best of them enough that I have given most of those that have come my way a trial in an effort to discover those that are effective in themselves or in planting schemes in the garden. Here I shall attempt to describe only those I have found to be the best and most serviceable, and to give my reasons for considering them to be so.
I can certainly agree that most of these plants might be called unnatural; they rarely occur in nature and when they do are usually weak and would not long survive. Ordinarily, I do not like unnatural effects in the garden: overly hybridized plants that have lost their natural grace, clipped hedges, geometrical schemes of any kind, including the modern sort, dismay me. I like to plant trees in groves and shrubs in groups inspired by, if not exactly imitative of, nature. But I do like plants with colored foliage; they seem to be a kind of enhanced nature. Why? Because, some would say, I like them; it is a mere matter of taste. However, the statements, “I like,” and, “You like,” have no meaning except as evidence about personalities; the only true information comes from answering the question, “What are my reasons?” and this brings us back to the things of the world and their configurations. The fact is that I travel through nature; the garden, on the other hand, is always there as home and as project. Nature may be my model, but it is, of necessity, nature remembered, reordered, and embellished, as the meter and rhyme of a poem remember, reorder and embellish its subject matter. I plan nature here and must always try to improve the alternations of plants, the colors, the entire environment. Moreover, I must try to surprise myself. Even though it is I who have placed these plants, when I turn a cover I want to be astonished as I am in nature when I come upon a stand of lilies or a field of annual flowers.
I can also agree with my friend that some plants with colored or variegated foliage have a highly superficial, decorative look that would make them impossible to place in a garden; but there are many more that can be beautiful in the right place. Therein, of course, lies the difficulty. We may be beguiled by a box of water colors; it is when we use them that we begin to appreciate the genius of a Cotman or a Turner. In general, I find that massed plantings of colored foliage shrubs and trees most often result in an over-bright artificial look, particularly when they are used as indiscriminately as they often are. In place of this blotchy look, I think every effort should be made to blend all plantings, a particularly demanding effort when colored foliage plants are involved. A golden foliage specimen, for example, may be planted with two or three red leaved shrubs, surrounded by deep green foliage and complemented with flowering perennials in a way that may be eminently satisfying. Or colored foliage may be used sparingly here and there as accents. A single, graceful variegated shrub can be beautiful planted at a turning of a path or beside a lawn. Here is how I phrase this to myself: Color obtrudes itself, therefore the problem is to fit it into — cause it to sink into an unobtrusive whole; a whole garden or landscape that obtrudes itself is a monstrosity. This is my rule, but, as we know, there are those who can occasionally break all rules with magnificent results.
The causes of foliage color and variegation form a very complicated topic. Here we can only summarize and make a few distinctions that may be helpful in understanding the behavior of the plants we choose to grow. Perhaps as many as one in two thousand seedlings of some genera of plants will show mutations in chlorophyll mechanism. Since, as I have said, these mutants usually do not survive long in nature, it follows that we owe the existence of those that are available to the selective activities of man, particularly gardeners and nurserymen. It further follows that those plants that have been longest in cultivation usually have the largest number of cultivars with colored leaves. There are at least six classes of causes of abnormal leaf coloration. In a few cases, the basic cause is simply structural; plant cells, particularly those of the leaf skin, may be blistered, causing an appearance of silver variegations. Far more often other pigments usurp the color producing role chlorophyll usually plays (the yellow pigments are called xanthophyll and the red ones anthocyanin). This may be because of an imbalance of pigments or because mutant cells have lost their ability to manufacture chlorophyll. Usually, an imbalance will result in a yellow leaf or yellow variegation. Unlike the yellow pigments, red is thought to be caused by a chemical action of abundant sugars and phenols in the presence of sunlight. This coloration may be present when the chlorophyll content in newly-formed leaves is low. This would account for those red foliaged shrubs and trees which turn green as summer advances and chlorophyll action steps up. (It is also important in fall when red coloration develops and chlorophyll activity declines.) Plant pigmentation occurs in layers and their superimposition often accounts for the very complicated patterns we see and that give rise to such names as “argenteo-marginata” and “aurea-maculata.” No one seems to know why these patterns occur with absolute regularity in some plants and haphazardly in others. In a few cases (many fewer than is often supposed) a virus infection which may be transmitted through several generations of cuttings or grafts, can cause variegation.
We should always remember that our Pacific Coast summers are on the dry side, especially when compared with Great Britain or Japan, and that many plants need moist air to arrive at their full luxuriance. In general, our climate is excellent for silvery and glaucous plants, since this coloration is one of nature’s means of combating the effects of drought, or heat, or both. However, for us, some golden shrubs or trees and a few red ones will burn with full exposure to the sun, although many others have proven themselves entirely hardy in this regard. Careful selection of plants and proper siting are therefore important.
One final introductory note: few plants maintain their special colors throughout the entire growing season, much less all year. Nevertheless, I should say that by colored foliage I mean that which remains so for a long time and not just new growth in spring or leaves about to drop in autumn, not because these are unimportant, but because they form a separate topic with a different meaning for gardeners.
Red and Purple Leaves
The number of broad-leaved trees and shrubs with red or purple foliage is severely restricted; they are far outnumbered by those that are yellow or golden, or blue or silver. Perhaps the most effective large tree with red or purple foliage is the famous (and, in England, ubiquitous) purple beech, Fagus sylvatica ‘Atropunicea’. There are several of these, all very beautiful, but the one most often sold in our nurseries is ‘Riversi’. It has dark purple leaves, but it is doubtfully preferable to any number of similar cultivars. Those with lighter colored leaves are generally referred to as copper beeches; Fagus sylvatica ‘Cuprea’, a name they well justify in some lights. These are all very striking trees in the spring, but, as Christopher Lloyd has said, they “soon settle down to a respectable middle age.” For some people they have the further disadvantage of keeping many of their dead leaves well into the winter. Nevertheless, they are beautiful and stately trees, best used as specimens in large gardens, parks and country places. The European beech does well on the Pacific Coast and accepts California sun, at least in the coast ranges. A specimen I planted in a meadow with a background of live oaks and redwoods adds color and a sombre diversity to the landscape without detracting from the naturally beautiful setting of a country house. Even the dun-purple color it assumes in summer is in keeping with the generally quiet, enduring look of the rest of nature at that time.
A more delicate and somewhat less spreading tree is Fagus sylvatica ‘Purpurea Tricolor’, which has smaller leaves edged with light pink. This tree also is hardy to the sun and very attractive in spring and early summer although it, too, turns a brownish purple in late summer. While it will in time grow into a large tree, it is more appropriate in habit and overall texture for a medium-sized garden. This tree is not to be confused with the cultivar ‘Tricolor’, a weak plant with pink leaf edges that turn white and burn in the sun.
Two other purple beeches are worth mention, if only because, unlike their cousins, they are eminently suitable for small gardens. The cultivar ‘Purpurea Pendula’ (really a shrub) makes an extremely slow growing mop-headed bush with beautiful, glistening purple leaves. The cultivar ‘Rohani’ has purplish brown, deeply lobed, oak-like leaves; it is a picturesque slow-growing tree that will remain under fifteen feet for many years.
Perhaps the reddest foliage of all large trees in spring is found in two cultivars of Norway maple: Acer platanoides ‘Crimson King’ and ‘Schwedleri’. As summer progresses, however, the first of these turns a dark mahogany color and the second becomes a dull green. Nevertheless, they are handsome trees, somewhat less spreading than the purple beeches but with large, shining leaves, and capable of serving much the same purpose in the landscape. I have planted these trees in hot locations — although not the hottest — with only faint traces of sunburn.
There are two purple-leaved oaks, Quercus robur ‘Purpurescens’ and Quercus petraea ‘Rubicunda’ or ‘Purpurea’. Q. robur ‘Purpurescens’ has purple new growth that changes in summer to a dun brownish color whereas Q. petraea ‘Rubicunda’ has reddish purple leaves that become dark green. Acer campestre ‘Schwerinii’ is another maple with purple new growth that turns dark green in late summer. An interesting tree is Catalpa erubescens ‘Purpurea’; its leaves also later turn green but the leaf stalks remain attractively purple. There is a purple leaved birch, Betula pendula ‘Purpurea’, but I have only seen it as a young plant. To the best of my knowledge this exhausts the list of large trees with reddish or purple foliage. All of them are deciduous; there are no large evergreen trees that could even remotely be said to have red or purple leaves. One of the beeches or the Norway maples is, therefore, our best choice for a large reddish specimen or for background effect — an effect, incidentally, that, for all its color, is a sombre one.
Fortunately, the field widens considerably when we come to the smaller trees. In my experience, the most effective of these is the red-leaved redbud, Cercis canadensis ‘Forrest Pansy’ (so-named for the Forrest Nursery Company in Tennessee where the cultivar originated). The leaves of this remarkable tree are both attractively glossy and definitely red — more so than any tree I know — and they remain red throughout most of the growing season. (They turn green on their upper surfaces only in autumn shortly before they commence a beautiful fall color display.) It is also an extremely serviceable tree, fairly drought tolerant and able to withstand considerable summer heat without burning. Our tree flowers, but never puts on that magnificent show for which redbuds are so famous. I account this a small matter; the tree is so eminently satisfying as a foliage plant that I feel it would be unreasonable to expect more of it.
The purple-leaved hazel, Corylus maxima ‘Purpurea’ forms a large suckering clump twenty feet high and as much across. Its fairly large, floppy, very rugose leaves are deep, bright purple in spring and early summer, becoming increasingly dark green as the season advances, and they have no beauty of color in fall or winter. Even so, I think this enormous shrub (which is what it is) is well worth its space, except, of course, in small gardens. The catkins, which have never been numerous on our plant, are also purple.
Undoubtedly the best known of all small trees with red or purple foliage are cultivars of the Japanese maple, Acer palmatum, and of these the most popular has always been the wide-spreading, low growing A. palmatum ‘Dissectum Purpureum’. Many seedlings of this plant resemble the parent, and a large number of different forms have entered the nursery trade. Most of these turn green in summer, but the cultivar ‘Crimson Queen’ can be relied upon to remain deep red throughout most of the growing season, and its leaves will change to bright scarlet in late fall or early winter.
Among the larger Japanese maples many have red leaves. Acer palmatum ‘Bloodgood’ keeps its color longest and usually has some red new growth even in late summer. It is usually thought to be a small tree, but, in the course of time, it will reach thirty-five or forty feet. I have always been particularly fond of the leaf shapes found among plants of A. Palmatum linearilobum, The red form of this, A. Palmatum linearilobum ‘Atrolineare’, makes an elegant small tree with picturesque, deeply cut, long-lobed leaves that hold their red color well into summer. Another very beautiful small tree or large shrub is the cultivar ‘Villa Taranto’, which has a spreading habit and a mixture of pink new growth and green older leaves. Many other colored forms of A. palmatum are described by J.D. Vertrees in his excellent book, Japanese Maples.
Almost everyone knows the red and purple leaved flowering plums, which are often used as street trees and in public parks. The oldest of these cultivars is Prunus cerasifera ‘Atropurpurea’ (‘Pissardii’) which has light pink flowers and purplish brown leaves. An improved form, P. cerasifera ‘Nigra’ has brighter, dark purple leaves and more decidedly pink flowers. It is probably the same as the cultivar ‘Vesuvius’. Perhaps the most popular of all is Prunus x blireiana, a hybrid between P. cerasifera ‘Atropurpurea’ and Prunus mume, with lighter purple leaves and double, light pink flowers. All of these are small trees, easy to grow, are not particular about soil and will take heat and reasonable drought. The cultivar ‘Nigra’ is a more vigorous tree than the blireiana plum; both grow to about twenty feet and have leaves that remain in color throughout the growing season. Although commonplace and often poorly used, these are beautiful trees. I think they are most effective grown, not as standards, as they are usually seen, but as large shrubs and as a background for lighter colored shrubs such as Teucrium fruticans along with herbaceous flowering plants.
Also in the genus Prunus is a delightful, faithfully red, small tree, P. x cistena, a cross of P. cerasifera ‘Atropurpurea’ and Prunus pumila. Prunus x cistena grows slowly to about six feet and is covered with white flowers in spring. There is also Prunus padus ‘Colorata’, a cultivar of the bird cherry, with dark purple leaves that change to deep green in summer.
I have never seen the purple leaved peach, Prunus persica ‘Foliis Rubris’, but I am certainly curious about it. E.A. Bowles, one of my favorite garden writers, says of it: “The most beautiful of all purple leaved things is certainly the purple-peach. It keeps its color to the end and constantly sends out young crimson growths through the whole summer. Its flowers are as rosy and large as those of the almond.” There will always be plants you want and don’t have.
There are crabapples with red foliage in spring, but none that retain their color long into summer. Perhaps the very best is Malus ‘Profusion’, which has masses of wine red flowers and red new growth. However, I am not fond of crabapples; they bloom spectacularly for a week, then even the best of them become sad-looking apple trees. Those that set interesting fruit do so among tired deciduous foliage. They perform better in cold climates where leaf drop is more sudden; the display of fruit on bare branches can then be spectacular.
For red foliage in the garden at or below eye level no plants are so useful and adaptable as the common Berberis thunbergii ‘Atropurpurea’ and its dwarf and variegated forms. B. thunbergii ‘Atropurpurea’ gets about six to eight feet high and nearly as much across left to its own devices. Extremely easy to grow, it will take heavy soils, reasonable drought and California sun. The dwarf form, B. thunbergii ‘Atropurpurea Nana’ stays under two feet and is easy to fit into almost any planting of small, mounding shrubs. The variegated B. thunbergii ‘Rose Glow’ has white variegation on the new growth that gives the shrub a lighter effect from a distance. All of these plants are spectacular when the sun shines through their leaves.
The purple leaved Venetian sumac, Cotinus coggygria ‘Purpureus’ can grow to fifteen feet, but it is usually much lower and can, of course, easily be kept lower by pruning. One of its best cultivars is ‘Notcutt’s Variety’ which has maroon-purple leaves somewhat lighter and redder than those of the Dutch raised ‘Royal Purple’. Both have pink inflorescences, but they are not of the size and magnificence of those of the ordinary green leaved C. coggygria. Cotinus coggygria, a Mediterranean native, is superbly drought resistant and a valuable addition to country gardens with limited water supplies. It is difficult to imagine anyone disliking its purple forms, which make excellent specimens even if there is no other colored foliage about. When the sun shines through the leaves they light up to a fiery red; planted with a groundcover of blue flowers it is guaranteed to win over even those hard hearts ordinarily oblivious to the entire range of colored shrubs.
There are few effective evergreen shrubs with red or purple foliage. Perhaps the best is Pittosporum tenuifolium ‘Purpureum’, which will in time become a small tree. The new growth is light green, but the leaves turn bronzy with age. While not very bright, it can be effective with plants with white variegation and it holds its color well in winter. We have recently acquired a dwarf form but I know nothing as yet about its behavior. The Australian Dodonaea viscosa ‘Purpurea’ is more frequently met with in the nursery trade; a rather crude large shrub that is more green than red in the growing season, it does have the advantage of bright red foliage in the cool season. A curious soft-leaved plant from New Zealand is Brachyglottis repanda, which has large leaves, purple above and white felted below. Closely related to senecio, it has more the look of an evergreen perennial than a shrub.
Another New Zealand shrub, Lophomyrtus ralphii ‘Purpurea’, is graceful with its masses of tiny leaves; it is a pleasant, quiet shrub whose color is closer to brown than to red or purple. One of the most frequently planted of all shrubs in California is Photinia x fraseri whose brilliant red new growth appears so continuously in summer that it perhaps deserve mention here. I find it a difficult shrub to use in the garden but almost everyone else, including most suburbanites and the highway department, seems to find it perfectly easy.
It should perhaps be mentioned that there are purple leaved forms of a number of shrubs otherwise chiefly known for their flowers or fruits. There is a purple Weigela (W. florida), a Euonymus (E. europaeus), a Sambucus (S. nigra), and there are two or three red-leaved hebes (Hebe speciosa cvs.). While all these are pleasant enough in their way, they do not add much color to the garden or landscape.
Golden and Yellow Leaves
The number of woody plants with wholly yellow or golden leaves is about the same as those with red or purple. However, their number would be much greater if we included those numerous variegated plants, such as Elaeagnus pungens ‘Maculata’, whose overall effect is golden. This, of course, is because there are a large number of plants with leaves that are green and yellow, very often in definite patterns; there are, to the best of my knowledge, no variegated woody plants with green and red leaves. For the sake of clarity, however, we shall later consider all variegated plants together, and discuss here only those trees and shrubs with wholly yellow or golden leaves, although this reduces their numbers somewhat misleadingly.
Care should be exercised in our climate, where winter rains often leach nitrogen from the soil and the summer sun not infrequently has a somewhat yellowing effect on ordinary foliage, to avoid a look of chlorosis when using golden plants in the garden. The plants used should be of a definite shade that is not one of chlorosis, and green plants in the garden should have their color deepened by the judicious use of fertilizers. Whatever colored effects may be desired, they can only be enjoyed in an overall atmosphere of plant health and vigor.
The best of all yellow-foliaged trees I have seen is the golden locust, Robinia pseudoacacia ‘Frisia’, which is seldom seen here but has long been used to add foliage color to many famous English gardens. Its discovery many years ago was a surprise to me since I had never placed the locust in the first rank among deciduous trees, despite its preeminent reputation in Europe. However, nearly everyone who sees it agrees that this cultivar is lovely with its masses of ferny, compound leaves that are soft yellow, remaining so all summer. The tree takes ordinary soils and does well on the Pacific Coast; I have planted it in hot locations and it has never suffered from sunburn. It is not to be confused with the locust, Gleditsia triacanthos ‘Sunburst’ that has bright yellow new growth that changes to green, and is much less graceful than R. pseudoacacia ‘Frisia’.
There are any number of large trees with golden foliage that, to the best of my knowledge, have never been given extensive trials on the Pacific Coast. For a bold, bright yellow tree perhaps none surpasses the golden catalpa, Catalpa bignonioides ‘Aurea’. It is worth quoting Bean: “Those who admire yellow-leaved trees will not find a more striking one than this; its leaves are wholly of a rich yellow, which does not become dull or greenish as the season advances, but rather improves in color.” Another tree that is faithfully golden throughout summer and is frequently grown in Europe is Acer negundo ‘Auratum’. There is also a yellow form of the silver maple, Acer saccharinum, with orange-yellow foliage in spring, and two yellow alders, Alnus incana ‘Aurea’ and A. glutinosa ‘Aurea’ that may well be suitable for us. We have grown plants of the golden beech, Fagus sylvatica ‘Zlatia’, in our nursery, but I would say that its leaves are not sufficiently bright to make it an effective garden subject. Where I saw the golden elm, Ulmus ‘Viminalis Aurea’, in Holland it had an extraordinarily cheerful effect in a land where the sky is so often overcast. One final tree deserves mention and that is the golden form of Quercus rubra. This tree turns green as the season advances but it is beautiful in spring. Donald Stryker had several of them in the woods surrounding his garden in southern Oregon and for a month or so they lit up the entire area and had the effect of large trees in bloom, an unforgettable sight.
If we are to consider golden shrubs in the order of their merit, then the first on my list is a very beautiful dwarf holly, Ilex crenata ‘Golden Gem’. This compact and dependably evergreen little shrub has small, glossy leaves that remain faithfully golden throughout the year, glowing and cheerful in winter and as bright as flowers in summer. Another very effective but much larger holly is Ilex aquifolium ‘Flavescens’, the moonlight holly. The leaves of this remarkable shrub are light yellow in the center shaded to a darker gold on the edges. Unfortunately they are liable to sunburn and need careful siting in most of California.
The two golden privets, Ligustrum ovalifolium ‘Aureum’ and Ligustrum x vicary, are not in themselves special beauties; in fact they are usually despised and described as commonplace, but as garden plants they can be very effective. In a sense, their very ordinariness is in their favor, since they can be made to fit into so many more locations than more distinctive shrubs. Both are more graceful than ordinary privets and both are only semi-evergreen, although they retain sufficient foliage in winter to add a cheerful, although somewhat ragged note, to their surroundings. Both are also useful in the shade where their color, then lime-green, is pleasant and avoids the look of chlorosis.
Although it tends to turn pale in winter, Lonicera nitida ‘Baggesen’s Gold’ is bright and yellow throughout the growing season. This makes an excellent clipped specimen and is fine for hedges. If allowed to go its own way, it should be watched for its widespread suckering and layering habit.
Another golden evergreen shrub of great promise is Abelia x grandiflora ‘Frances Mason’, a new cultivar still small in our garden, but its color is outstanding; golden throughout with reddish tips on new growth.
In addition to these evergreen and semi-evergreen shrubs, there are a number of deciduous ones with golden foliage. Yellow-leaved plants have been found of the ordinary lilac, the mock-orange (Philadelphus), Viburnum (V. opulus), a weigela, a flowering currant (Ribes sanguineum), a hazel (Corylus avellana) and a number of other well known garden subjects. Most of the shrubs in this class, however, are not good for colored effects in the landscape. Thus, for example, the foliage of the weigela contrasts very prettily with its pink flowers, but it is a shrub that soon turns a rather chlorotic green. There is a yellow barberry, Berberis thunbergii ‘Aurea’, but it is far from being as effective as B. thunbergii ‘Atropurpurea’. The golden hazel is likewise only faintly golden and no match for its purple cousin. Two significant exceptions to this appraisal, however, are the full moon maple, Acer japonicum ‘Aureum’, and a beautiful golden elder, Sambucus racemosa ‘Plumosa Aurea’. The maple is, unfortunately, very apt to burn on the Pacific Coast and can only be grown with extremely careful siting (some sun to keep the leaves golden, but sufficient shade to prevent sunburn). The sambucus is more hardy, and its large, finely divided golden leaves are excellent for grouping with perennials.