Areas where there is little direct sunlight and which it is uneconomic or otherwise impracticable to water — near mature evergreen trees for example — provide some of gardening’s greatest problems. The author, a partner in Western Hills Nursery, offers some suggestions for planting such places.
Nature herself (and not just the local nurseryman) often does not give us the plants we need. From leisure world the cry is heard: “I dream of a Japanese garden.” A voice replies: “Japan is far away, mosses will not grow nor maples nor azaleas in your sun and Santa Ana winds.” It is Nature who speaks, and the prudent man listens, plants a weeping Atlas cedar, some Irish moss and a cast stone lantern. His garden, if not Japanese, is “Japanese,” and who will begrudge his contentment?
There are degrees of difficulty in finding the plants we need. For some situations — gardening on sand, gardening on clay, in sun, in shade — there are suggestions to be found in the Sunset Western Garden Book, in Bean’s Trees and Shrubs, in Lord’s Shrubs and Trees, in Graham Stuart Thomas’ excellent books on perennials and groundcovers, and in many others. More difficult are such special situations as reclaimed salt-flats (the Dutch literature has never been translated, and the local literature was printed before the plants had a chance to die ), or combinations of requirements: we may need plants for soils that are both water-logged in winter and parched dry in summer; or we may need evergreen vines that are tolerant of baking sun and are frost-hardy. Though such plants exist, information on them is hard to find.
Areas both dry and shady are very frequently met with in Pacific Coast gardens, and it seems useful to bring together a list of plants for these awkward situations. Two prefatory remarks are needed: in the first place, “dry shade” is obviously a relative term. We are not talking of the Atacama desert, but of basically unwatered areas under trees or those shaded by overhead structures. Nor are we thinking of absolute darkness, as in a mushroom factory, but of such moderate to deep shade as might, again, be found in the shade of trees or buildings.
Secondly, I have a prejudice in favor of first-hand information, however meager, since so much misinformation trickles down from book to book. Though I may cheat a bit, the plants mentioned are chosen for their behavior in a particular garden in the coast hills to the north of San Francisco, with heavy winter rainfall; moderate frost and some fog and cooling from the ocean. The selections must be viewed with caution by those in warmer or colder areas.
Massive alphabetical listing of plants, though useful for reference, is a bit long in the reading. Instead, I have chosen to list plants by geographical areas: first, those from the five dry-summer Mediterranean climate zones, and then those shade plants from summer rainfall areas which, nonetheless, seem to accept drought. It is my hope that this geographical approach might point the way to other plants as yet untried.
To organize the following necessarily discursive notes, I plan, roughly, to go from trees to shrubs, from perennials to ground covers. The garden uses of West Coast plants are so well documented in books (starting with Lester Rowntree’s classic Flowering Shrubs of California), and in the journal Fremontia, and so well demonstrated in botanic gardens like those at Rancho Santa Ana in Claremont, and Tilden Park in Berkeley, that only brief notes are needed. We look, of course, to the understory vegetation of our climax forests. For conifers, I shall list only Torreya californica, though the two hemlocks might accept drought if shaded. Small broad-leaved trees include Ceanothus thyrsiflorus, Fraxinus dipetala, Myrica californica (later to be listed also as a shrub), and Acer circinatum, which is surprisingly drought tolerant in our area.
For shrubs, going quickly, we would include the huckleberry; Rhododendron macrophyllum; Rhamnus californica and its smaller varieties; Myrica californica, that most adaptable of California shrubs, with its mutant box-leaved form; the various scrub-oaks; and the two dwarf tanbark oaks, Lithocarpus densiflorus var. echinoides, and the fearsomely named sublethal mutant, Yuba sawtooth tanbark oak, L. densiflorus forma attenuatus-dentatus. Surprisingly, we can add Dendromecon harfordii which grows and flowers splendidly under the oaks at Rancho Santa Ana. Mahonia aquifolium we rule out for most purposes as a suckering nuisance, but its dwarf forms and M. nervosa and M. pinnata have their place.
Low plants include heucheras, tiarella, Dicentra formosa, the dowdy but serviceable Whipplea modesta, Tolmiea menziesii and its golden variegated cultivar, and the remarkably drought-hardy Vancouveria hexandra and V. planipetala. Dave Verity’s hybrid diplacus are drought resistant and said to appreciate some shade. We shall list them, though their gorgeous colors almost lift them out of the category of native plants.
A few ground covers include the West Coast’s two great contributions to the dry-shade garden, the sword fern, Polystichum munitum, and Oxalis oregana; polypodiums, smilacina, Sedum spathulifolium, Arctostaphylos nummularia, Ribes viburnifolium and unexpectedly, Ceanothus griseus var. horizontalis, which can also be seen under the oaks at Rancho Santa Ana.
These notes are obviously scanty and incomplete, but information is so easily to be had that I shall turn now to the next area.
The Mediterranean Basin
Here too we look for understory plants from dry but dense climax woodlands, in this case, mostly Quercus Ilex. Among large shrubs (or small trees) we include Osmanthus decorus (Phillyrea decora); Rhamnus alaternus in its green and variegated forms; Laurus nobilis; the hazels, including contorted and yellow and purple cultivars; Ilex aquifolium in all its forms; Arbutus andrachne and Arbutus unedo. The last, the strawberry tree, has an excellent dwarf form, ‘Elfin King’, selected and introduced by Ponto Nurseries in San Diego County. It is a small shrub growing to four feet with a plentiful display of flowers and large fruit. For moderate shade in dry places we may add the smokebush, Cotinus coggygria, and its purple forms.
Shrubby plants include, of course, the classic boxwood, myrtle and yew; the butcher’s brooms, Ruscus aculeatus and R. hypoglossum. The evergreen Cretan maple grows for us in shade, though it is perhaps more of botanical interest than garden value. The twin invasive horrors, Hypericum calycinum and Vinca major, we shall try to exclude since they may survive drought, but have not the grace either to flourish or to die.
Turning to perennials and ground covers, there is such a wealth as to defy listing. Some, such as the common foxglove, Digitalis purpurea, and Asperula odorata, sweet woodruff, are so suited to dry shade that they have naturalized in many wooded areas of the Pacific Coast. Others, like Corydalis lutea and Geranium macrorrhizum, are among the most reliable groundcovers we have. Campanula primulifolia naturalizes itself in the driest shade. I include one bulb, Scilla peruviana, because it accepts shade as well as sun. Acanthuses we shall omit since, though they survive drought, they develop a dejected look.
To avoid becoming overwhelmed by their numbers, I will finish with the plants I consider to be the most important for dry shade: euphorbias, epimediums, and hellebores. Most of the Mediterranean euphorbias are from open sunny locations, but at least three are fine plants for shade. Euphorbia cyparissias deserves its reputation as invasive, but, where it can be allowed, will compete successfully with the worst tree roots in deep shade and make a solid mat of bright green soft-needled shoots six or eight inches high. Euphorbia robbiae, that plant mysteriously found once by Miss Robb in Greece and never found again, has handsome deep green rounded leaves and chartreuse flowers in spring. I suspect it would appreciate a little water, but such a handsome plant must be included. Euphorbia epithymoides is a third species, with rounded green domes to one foot, possibly invasive by seed, but tough and showy in difficult places.
Epimediums, the Old World equivalent of our vancouverias, are sharply divided into two groups. The Japanese species are deciduous and require summer water, but the evergreen species from the Mediterranean basin are superbly drought resistant plants. Epimedium perralderianum is from Algeria, E. pinnatum subsp. colchicum from east of the Mediterranean. Both have bright yellow flowers but there are several hybrids, of which E. x warleyense, with copper red flowers, is the best known.
Now we come to the hellebores. One, Helleborus niger, from Northern Europe, with large white flowers, falls outside our range, but the others are fine plants for drought and shade. There are a number of species and ill-defined cultivars. For our purposes we may reduce them to three: H. orientalis and its related forms with pink, white or purple, often spotted, flowers and relatively uninteresting palmate leaves. Helleborus lividus subsp, corsicus with very bold blue-green broad leaves and striking chartreuse flowers in very early spring; and Helleborus foetidus with black-green narrow leaves and chartreuse, maroon-spotted flowers, also in early spring. These are among the most handsome foliage plants we can grow in moderate to deep dry shade.
Before leaving this area, we might cast a glance at the Canary Islands and Madeira, though their plants tend to be frost tender and prefer coastal conditions. One magnificent evergreen tree might be mentioned, Clethra arborea, here accepting dry conditions, and giving spikes of fragrant white flowers; and one handsome self-sowing perennial, Geranium palmatum (G. anemonifolium), which survives and naturalizes in the most impossible places. Many more plants could be mentioned, for example the aeoniums, but the reader is referred to the Bramwell’s Wild Flowers of the Canary Islands, in which detailed habitat descriptions will suggest a number of plants.
This, the smallest of the summer-dry areas, is also, perhaps, the least interesting. The small trees we have grown, such as quillaja, kageneckia, schinus, and Lithraea caustica, are much of a piece, with nondescript leathery leaves reminiscent of our live oaks and no floral beauty. The azaras have more handsome foliage and desirable flowers, either chocolate-scented as in Azara microphylla, pendulous in A. petiolaris, or showy sulfur-yellow in A. serrata. They are, however, large trees at maturity, and so fall doubtfully into our class of understory plants, though accepting shade. One conifer should be mentioned, a very hardy tree which has been unaccountably neglected, Podocarpus salignus, with dark green foliage, graceful habit, and, like many others of its genus, quite tolerant of shade and drought.
Turning to shrubby plants, I must simply confess ignorance of what central Chile might have to offer. In order not to leave a complete blank, attention might be called to the escallonias, which are drought tolerant and very likely will accept shade. I find them generally uncharming, and have, perhaps, not given them a fair trial. Other plants with potential for dry shade may be found among the barberries. Here we probably move south of the Mediterranean area of Chile in mentioning Berberis darwinii, the many forms of B. x stenophylla, B. lologensis ‘Orange King’, just now becoming available, and, finally, that beautiful foliage plant, Berberis hakeoides, as seen in Strybing Arboretum, a plant which successfully resists propagation.
Again, my knowledge of perennials and ground covers native to central Chile is extremely limited, and l will limit myself to mention of three genera, all of which, however, contain some of the very best plants for dry shade. There are a number of alstroemerias in Chile, most with special requirements, but the hardiest and most commonly grown, Alstroemeria ligtu, A. pulchella and A. aurantiaca and their various cultivars, grow very well in shade under trees and, when established, are almost ineradicable, since their tubers go deep into the ground. Francoas are also drought resistant and shade-tolerant and two are in general cultivation, Francoa ramosa, with white flowers, and F. sonchifolia, with pink. Both are plants with somewhat coarse foliage, but pleasant upright spikes of flowers, and they are indispensable for difficult situations. The third plant that merits mention is Modiolastrum lateritium (Malvastrum lateritium), an excellent ground cover in sun or shade, with apricot pink mallow-like flowers.
Strictly speaking, following our format of Mediterranean areas, we should be limited to the Cape Province. But, as later with Western Australia, it would seem that the summer-dry areas are more or less lacking in forest, and are essentially bush and scrub — though these words scarcely do justice to the beauty of the ericas, leucospermums and leucadendrons, or to the rather brash showiness of proteas. (A friend remarked that proteas look like something an interior decorator did to an artichoke.) Should one want proteas, however, Marie Vogts tells us that Protea cynaroides, the biggest flowered and hardiest of all, does tolerate shade, and there is no question of the drought tolerance of proteas from areas of winter rainfall. Preparing these notes and leafing through Sima Eliovson’s excellent South African Wildflowers for the Garden, a curious fact emerges: it seems that many South African plants are more drought resistant for us than they are in their native habitat. This is completely contrary, as we shall see, to the situation of many New Zealand plants claimed to be drought tolerant but which pine away in dry situations here.
For large shrubs or small trees, we can mention the beautiful blue-green long-needled Podocarpus henkelii (whose name has been oddly corrupted in nurseries to P. “henryi”), Sparmannia africana, the Zimmerlinde of German households, and its spectacular variegated form with clearly demarcated snow-white zones on the leaves. Sparmannia will take perhaps twelve degrees of frost and tolerate deep shade and drought very well. Smaller shrubs with which I have had experience include Mackaya bella, with beautiful shining undulate leaves and odd papery pink bells, and Bowkeria gerardiana, roughly a shrubby white-flowered calceolaria in appearance. Finally we come to a fearfully rampant plant, growing well in sun or shade in any area with less than twelve or so degrees of frost, Helichrysum petiolatum. Oddly enough, this plant is not mentioned by South African writers and comes to us in a roundabout way from England, where it has long been used like pelargoniums for summer pots and bedding schemes. There is a variegated form and, especially to be recommended for lightening up dry shady corners, the chartreuse-yellow flowered cultivar ‘Limelight’.
For the most part we have ignored bulbous plants in these lists. South Africa, however, is so rich in them that some should be mentioned. Agapanthus orientalis, eucomises, some kniphofias, and the supposedly moisture loving dieramas are all good plants for dry shade. Succulents, again, have not appeared in our lists, and we shall just mention that a number of aloes and gasterias accept drought and shade with good grace.
This, the last of the Mediterranean areas, presents us with the same problem as does the Cape Province: the spectacular shrubs of the sand-plains grow in low bush country with little overhead shading. The Karri forest, to the south around Albany, on the other hand, though having a rich understory, is a well-watered area of heavy rainfall. Some of these understory plants, however, have proved quite drought resistant for us here. Among these are Hardenbergia comptoniana, Clematis aristata, Chorizema ilicifolia, C. cordata and kennedyas. The blue-flowered hoveas we have not succeeded in establishing.
It is unfortunate for our purpose that the wonderful collection of Australian plants grown at the University of California, Santa Cruz Arboretum is still too young to have established overhead shading, and can, as yet, give us little guidance. A search through the pages of Australian Plants will undoubtedly suggest shade-loving acacias and other plants for trial. Two trailing grevilleas which grow in shade in nature and are drought resistant are Grevillea laurifolia and its hybrid G. x gaudichaudii. Two pittosporum relatives have proved themselves, Sollya heterophylla and Billardiera erubescens (Marianthus erubescens). The beautiful blue-berried Tasmanian, Billardiera longiflora, unfortunately will not be at its best without water.
Promising plants for dry shade are hibbertias and correas. Certainly Hibbertia cuneiformis (Candollea cuneiformis), though from the Karri forest, has proved very satisfactory, as has the vining H. dentata. Hibbertia volubilis, though a seacoast plant, does very well in shade. Correas, as a whole, are drought resistant, and tolerate shade as well. For special mention we might single out Correa decumbens, quite prostrate, with upright tubular flowers, and Correa reflexa ‘Dusky Bell’, as it was originally named by Ralph Boddy, which is sometimes seen as ‘Carmine Bell’. This, though the flowers are perhaps too dusky and not well presented above the leaves, is a very fine densely foliaged and weed-suppressing plant for dry shade under trees. Correa reflexa ‘Yanakie’, a little sprawling in habit, has the brightest red and yellow flowers of any. With this we end the short survey. Availability of these plants is still so slight and my first-hand knowledge so scanty, that it is impossible to do justice to what is undoubtedly a very rich field.
Japan, China and Formosa
Up to this point we have been dealing with the Mediterranean climate areas of the world. There seemed a certain logic in looking for dry-growing plants in dry areas and it provided a framework for what might otherwise be an unrelenting list. Turning now to the rest of the temperate world — Japan and Formosa, China and Tibet, Northern Europe, New Zealand, Eastern United States and Mexico and South America — we encounter two problems. First, since there is no particular reason why certain plants from summer rainfall areas should be drought tolerant, our list will be much more fragmentary. Secondly, to repeat a caveat earlier stated, the following selections are quite empirical and, in a sense, accidental: they are plants which we, in fact, have found will grow well in dry shade in our area. Gardeners in warmer or colder areas must supply their own reservations and add their own choices. For example, totally damning Hypericum calycinum as a dilapidated suckering menace in California does not take account of the fact that it prospers throughout the summer in coastal Oregon and Washington and might there be almost worth growing.
We turn, then, to Japan. First and foremost, Ilex crenata, the Japanese holly, is indispensable for dry shade. Roughly, it serves much the same purpose as boxwood, and many of its cultivated varieties — dwarf, bun shaped, upright, curled, golden, and so on — parallel the many cultivars of box. Of larger shrubs we shall list only Podocarpus macrophyllus, familiar from so many shaded entryways. Lonicera japonica will grow in deep dry shade and is particularly useful in its gold-netted form, L. japonica ‘Aurea-reticulate’. For low-growing plants we have a surprising candidate, the Japanese wood iris, Iris japonica and its variegated cultivar which Mr Giridlian distributed under the name ‘Aphrodite’. This has flourished for years without water under a bald cypress. Aspidistra elatior, of which there is also a white-striped version, can be added here, but the more interesting and rarer cultivars, A. minor ‘Milky Way’, with spotted leaves, and the white tipped ‘Asahi’, probably need more coddling, and certainly more protection from snails and slugs. Its smaller relative, Rohdea japonica is similarly drought-resistant, and again its choicer cultivars, some of which are enormously expensive and bought by Japanese in lieu of Krugerrands, belong in their special elongated pots and not in the garden.
The reader will be grateful that I do not intend to list the enormous number of cotoneasters, from large bushes like Cotoneaster ‘Cornubius’ and C. lacteus to the ground covers. Many will grow in the most difficult conditions. Fireblight was for us the problem, as it was with the related stranvaesias. More surprising, perhaps, are the Japanese quinces, or chaenomeles, which will accept dark dry conditions. (This I learned from Sima Eliovson’s Complete Garden Book.) Other Chinese shrubs include the hollies, Ilex cornuta, the dwarf I. cornuta ‘Rotunda’ and the upright Ilex pernyi, which combines beautiful small leaves with pendulous branches, and grows for us in the deep shade of a live oak. Daphne odora, usually thought to have come to Japan from the camellia zone of China, does best for us in almost totally dry shade in summer. Finally, we shall mention one perennial, the Japanese anemone, Anemone x hybrida and its cultivars, which, when established, are indestructible in dry shade. We turn to Formosa for an indispensable ground cover, Rubus calycinoides which takes drought either in sun or shade and makes a handsome dense carpet.
Here we shall just mention a few plants not included in speaking of the Mediterranean basin. Iris foetidissima, a shade plant valued for its red seeds held in gaping pods for many weeks, I. foetidissima var. citrina with yellow flowers, and the handsome I. foetidissima ‘Variegata’ all do well in deep dry shade. The biennial honesty, Lunaria annua, both in its mauve and white flowered forms, has naturalized in dry woods in our area, and is handsome in flower as well as valuable for its silvery replums familiar in dried flower bouquets. The sedge, Carex pendula, is serviceable, and provides textural interest in shade.
In speaking of South African plants, we mentioned that many listed by South African writers as needing water are unexpectedly drought resistant for us. With New Zealand plants the opposite seems to be true. Years ago, Brian Halliwell, who had just returned from that country, visited us and remarked that our climate seemed the same as that of Christchurch in New Zealand, and we could easily grow the giant Chatham Island forget-me-not, Myosotidium hortensia, or the giant Ranunculus lyallii. We have succeeded with neither.
Cotulas and acaenas, from New Zealand, though unrelated, have much the same habit and uses. George Schenk, that fine and eloquent gardener from Washington now living in New Zealand, was very much interested in these plants, and had collected quite a number. In general they are very low matted groundcovers with interesting textural and color differences, reputed to grow in dry shade and tree roots right up to the trunks of conifers. For us they simply needed water. Cotula squalida, potentially a handsome bronzy-green substitute for moss, gradually died out under an alder unless given supplementary sprinkling. Another shade plant, Dianella intermedia, grew but would not produce its metallic blue berries without watering.
In short, it is not to New Zealand we look for candidates for dry shade. Three exceptions can be made: Podocarpus totara, a fine, short-needled conifer that can be espaliered, trimmed or twisted as one likes, Libertia formosa, an iris relative with the usual sword-shaped leaf blades and three-petaled white flowers; and the shrubby daisy, Pachystegia insignis. This, with evergreen leathery leaves, green on top and white underneath, and showy white-rayed, yellow-centered flowers, is an elegant plant indeed, slowly growing in dark dry positions.
Eastern United States
Though blessed with summer water, our Midwestern and Eastern States do provide us with some fine drought-resistant plants. Physostegias and stokesias, for example, grow and flower in the driest situations. Dry shade is, of course, a more difficult proposition. From experience I shall mention only two plants that have done well for us: Galax urceolata (G. aphylla), a handsome foliage plant, and the large Solomon’s seal, Polygonatum commutatum. It seems very likely that a regionally minded nursery, such as the Woodlanders, which offers plants from the dry sandplains of the South Carolina seaboard, may provide other candidates.
Mexico and South America
An enormous area is lumped together only to call attention to a very few plants. Mexico is of especial interest to those of us in the milder California areas, because of the extensive introductions made in the last few years. It might well be singled out as our horticultural frontier, as China and the Himalayas were for England in the great days of plant exploration. Especially notable have been the gigantic and gorgeous salvias which, however, seem to have an inordinate thirst for water, wilting in sun if grown in dry conditions. The various cestrums, however, do very well in dry shaded positions. Turning from these large weedy shrubs to ground covers, there are two alchemillas, Alchemilla pectinata and A. guatemalense, which we originally obtained from the University of California, Berkeley, Botanic Garden, where they have been grown for some years. Both are excellent and vigorous growers in dry shade, serving much the same purpose as Rubus calycinoides, but with softer green leaves and a faint mist of inconspicuous flowers appearing over them. Unlike the more familiar European lady’s mantles these alchemillas are suckering plants which quickly form a carpet.
Finally, we turn to South America, but will add only a few shrubs to the list. The iochromas have the gangling habit of cestrums, but add different colors, dark red, or, as in Iochroma cyanea, a fine dark blue, to the shade garden. I am not on firm ground in speaking of fuchsias, but Fuchsia magellanica var. macrostema is certainly drought resistant and, along with a number of the other small-leaved species, deserves trial in dry shade.
In speaking of Chilean plants we omitted the distinctive light blue or white Corynabutilon vitifolium (Abutilon vitifolium) and its hybrid with C. ochsenii, A. x suntense. These are certainly supremely drought resistant plants but, I think, need a fairly open situation to grow and flower at their best. The other flowering maples are divided roughly into two groups: Abutilon megapotamicum, its allies and cultivars, with smallish leaves, more vining habit, and smaller yellow flowers appearing out of a red calyx (here belong Victor Reiter’s ‘Marianne’ and some of Jack Catlin’s selections); and those, familiar, but of uncertain parentage, with large bell or bowl shaped flowers in white, pink, red, orange or yellow. All of these, at least in coastal areas, succeed very well as an understory in dry woods.
With this we end our list. Like the coin collector who feels the lack of a 1906 Indian-head penny to “complete the series,” the reader will feel as I do, the omission of many plants which should have been included. Further he will feel the lack of qualifying remarks and cautions which, for lack of space or lack of knowledge, have not been made. In short, the list just concluded is necessarily inelegant and incomplete, but my hope is that it will at least focus attention on the problem of dry shade — a problem that can be a source of interest as well as frustration for the puzzled gardener.