Trees, shrubs, and vines are basic plants for the container garden. They provide height and background, accent, and shade. Since nurserymen and garden centers offer them in bushel baskets, large tin cans or simply balled and burlapped, they are easily planted in permanent containers. Growing trees and shrubs in tubs and boxes is a widespread practice in climates with scant rainfall, like our Southwest and the Mediterranean countries, but gardeners everywhere can treat them as specimen plants. They lend distinction and grace to the large terrace or outdoor sitting area and are effective at doorways, along walks, on driveways, on terraces, and around swimming pools. One great advantage of containers for trees and shrubs is that you can experiment with kinds that are tender in your climate. Oleanders, lemons, oranges, Chinese hibiscus, and camellias are all possibilities for northern gardeners. Unusual varieties of these and others can be tried, and you can give special attention to rare kinds.
Value of Trees
Trees contribute the element of height and the structural beauty of their trunks and lower branches, especially in winter, if they are deciduous. Some like stewartia and eucalyptus have colorful exfoliating barks that give winter interest. Trees also cast shade for sitting areas as well as for plants and create fascinating shadows on pavements and walls. As a rule, small foliage or flowering trees-Japanese maples, crab-apples, Oriental cherries, and dogwoods-are best, since they require infrequent repotting. Slow growers, tupelo and ginkgo, are also valuable because they remain useful for long periods. Yet even large trees can be grown successfully in containers. Garden centers carry Norway and Crimson King maples, lindens, oaks, yellow-wood, plane trees, and honey-locusts. When the trees get too large, transplant them to the garden or give them away.
Value of Shrubs
Shrubs are easier to handle because they are smaller and require less space. For mass effects and backgrounds, rely on large kinds, either hardy or tender, the latter for an exotic touch. Nowadays, shrubs, like trees, can be planted at any time because they are available in boxes, tins, or bushel baskets. This makes it easy to transfer them to tubs or boxes without disturbing the roots.
Allow for Evergreens
The container garden is not complete without some evergreens, especially in regions where the garden can be enjoyed on pleasant late autumn, winter, or early spring days. Well located evergreens are also appreciated from indoors. Balled and burlapped or container-grown, tree and shrub types can be obtained throughout the growing season. For interesting effects, combine evergreens with deciduous trees and shrubs-cherries, crab-apples, deut-zias, and viburnums. With careful clipping, hemlocks, pines, yews, and arborvitae can remain in the same containers for several years. Remember, too, to include some broad-leaved hollies, azaleas, rhododendrons, and camellias.
What trees are hardy in the colder regions of the North? Which are recommended for the warmer South? These general questions are difficult to answer because hardiness is variable; each section of the country has its own definition. As gardeners, we are constantly learning what will and will not do in the areas in which we live. Nevertheless, there are certain trees that are considered hardy in regions where temperatures go well below freezing. For these sections, here are some of the more desirable kinds:
Birches. Graceful trees for containers. Clumps of the native gray, white or paper, or weeping European birches are desirable for the contrasting bark. Small leaves cast light shade.
Crab-apples. Lovely hardy flowering trees, with red, pink, purple, or white blossoms in spring and colorful fruits in fall, much favored by birds. The smallest one, which can be pruned to picturesque form, is the white-flowering Sargent crab-apple, as broad as it is tall. Choice hybrids include Dorothea, Dolgo, Flame, Hopa, and Katherine.
Dogwoods. Many kinds, including flowering dogwood, with white or pink flowers in spring, brilliant fall coloring, and interesting winter form. The Japanese kousa dogwood blooms later and continues for several weeks. For the West Coast, there is the upright Pacific dogwood. Cornelian cherry, a true dogwood, bears tiny yellow flowers in early spring.
Dove Tree or Davidia. Where reliably hardy (a specimen at Arnold Arboretum, Boston, blooms periodically), an unusual tree, with large white bracts among heart-shaped leaves in spring. Requires special care, but is worth the effort.
Franklinia or Gordonia. Like the dove tree, also requiring special attention. Single, camellia-like, cream-white flowers open in late summer and continue until frost. Leaves are colorful in fall. Barely surviving winters around Boston, this is reliably hardy from New York City southward.
Fringe Tree. Large shrub or small tree, with fluffy, white flowers appearing with unfolding foliage in late spring. Shows up strikingly against evergreens.
Ginkgo. One of the best, very hardy and slow growing with a fascinating form. Also called maidenhair tree, it transplants easily. A fastigiate variation, the Sentry Gingko, will give accent. Golden-Chain Tree or Laburnum. Small ornamental tree with pendulous, wisteria-like, golden flowers in spring. It will attract much attention in a large plant box.
Golden-Rain Tree or Koelreuteria. One of few yellow-flowering trees for the North. Compound leaves are highlighted by upright panicles in midsummer, followed by pods that change through several colors. Golden-rain withstands drought.
Hawthorns. Many kinds, with showy red, pink, or white flowers in spring. Outstanding is the English hawthorn, including the red Paul's Scarlet and Arnold hawthorn with white flower clusters. Washington thorn has bright red berries in fall.
Hollies. Pyramidal broad-leaved evergreens with handsome foliage and sparkling red berries. American holly is hardier than English, but both have forms with variegated leaves and yellow or orange berries. All withstand formal clipping.
Japanese Red Maple. Dainty, with divided dark leaves and a horizontal habit. Varieties have deep-cut green leaves (Acer palmatum dissectum) or purple foliage (A. p. atropurpureum). Much grown in containers on the West Coast.
Japanese Snow bell or Styrax. Small and spreading, with myriads of exquisite white bells in early summer hanging from underneath the horizontal branches.
Japanese Tree Lilac. The last of the lilacs to bloom, with large, fragrant, cream-white tresses in early summer. Very hardy and slow growing, it can be trained with one or several trunks.
Magnolias. Many kinds with showy flowers. Earliest to bloom is the star magnolia in white or pink. If spring frost threatens, move to shelter during night. Next to flower is the common saucer magnolia in white, pink, rose, or purple. This has an interesting habit and soft gray bark. Sweet bay magnolia produces fragrant, cream-white flowers over a period of weeks during the summer. Attractive dark green leaves are whitish beneath.
Moraine Locust. Recently introduced variety, with fine compound leaves and an open, graceful habit. Fast growing, and pest-free with neither thorns nor messy seed pods. Sunburst locust, another variety, is noted for its golden-yellow tips.
Mountain Ash. Showiest is the European with a loose habit and white flowers in spring followed by rich clusters of orange-red fruits. Fast-growing plants offer filtered shade.
Oriental Flowering Cherries. Small trees, with single or double, pink, rose, or white flowers in spring. Unique is the weeping cherry, with very early pink blossoms. Variety Kwanzan, a narrow, upright grower, has large double blooms resembling roses.
Pines. Choice depends on climate and personal preference. The red, pitch, Scotch, Austrian, and Japanese black pines are seashore subjects, but all pines take well to container culture if kept moist and not neglected in winter. They do best in sun and can be pruned or sheared.
Poplars. Fast-growing, weak-wooded trees, easily replaced because they are readily obtainable at reasonable prices. The slender Lombardy poplar can be planted for accent or a hedge. All easy for the container garden.
Redbud or Judas Tree. Small, with rose-pink flowers in tight clusters and heart-shaped leaves. The eastern common redbud is the hardiest, but in milder climates the Chinese redbud is equally lovely.
Russian Olive. Admired for silvery leaves and the crooked trunk and branches it develops. Very hardy and vigorous, fine for the seashore because it withstands wind and salt spray.
Silverbell or Halesia. Upright tree with tiny bells in white or pink at dogwood and tulip time. Locate where it can be observed closely.
Scholar Tree or Sophora. A member of the pea family, with compound leaves and cream-white flowers in midsummer. Tolerates dust and soot of cities.
Sourwood or Oxydendrum. Small summer-flowering tree, with drooping clusters of small, fragrant flowers and lustrous leaves that turn scarlet in autumn. In containers, specimens can easily be provided with the acid soil they need.
Stewartias. In summer, the Japanese stewartia has white blooms with orange stamens, and the showy stewartia has white blossoms with purple stamens. Both have colorful autumn foliage and rough barks.
Weeping Willows. Among the best trees for rooftops because they withstand wind. Fast growing, they need periodic replacement, but young plants are moderately priced. The Golden Weeping Willow has bright yellow twigs in winter and chartreuse catkins in early spring.
This is only a partial list of hardy trees for the container garden. Almost any kind can be grown if in scale and given the necessary care. Do not overlook fastigiate forms-upright lindens, oaks, sugar and Norway maples -since these take up little space.
Tender trees are commonly grown in warmer regions, where they remain outdoors all year. In colder areas, as container subjects, they require shelter in winter. As a group, they are popular with both southern and northern gardeners.
Acacias. Many kinds of acacias are treasured for their feathery yellow flowers in winter and early spring. Fast growing, they require a cool greenhouse or plant room in the North in winter.
Bullbay Magnolia. A highly ornamental evergreen magnolia, much grown in the South, with large dark green leaves and huge fragrant white flowers. Where not hardy, a most worthwhile container plant.
California Pepper Tree. A semipendulous small tree, with fernlike, olive-green leaves and hanging clusters of long-lasting, rose-colored berries. A native of Peru, it withstands heat and dryness, even poor soil, as well as severe pruning. Much planted as a street tree in southern Europe.
Citrus. Glossy-leaved trees, with small, scented flowers and decorative, lasting fruits. Orange, lemon, kumquat, tangerine, lime, and others do well in tubs and boxes. The dwarf Otaheite or Tahiti orange and the Ponderosa lemon are small types.
Crape Myrtle. The "lilac of the South," a shrub or small tree, with great tresses of crinkled blooms in pink, red, purple, and white all summer long. Container-grown in the North, it must be wintered in a cool frost-free place. It withstands severe pruning.
Eucalyptus. Rapid-growing, drought-resistant trees with leathery aromatic leaves and peeling bark. Replacements of container specimens are easily made.
Japanese Privet. A handsome tall shrub or small tree, with glossy, dark green leaves and panicles of white flowers, followed by black berries. It is often confused with the less handsome glossy privet (Ligustrum lucidum).
Loquat. A Japanese tree with long, leathery, strong-veined leaves and tasty orange-yellow fruits. An excellent tub specimen for terraces or patios, as often seen in southern Europe.
Norfolk Island Pine. A pyramidal, horizontal evergreen with sharp-pointed leaves. Much grown as a pot or tub plant in greenhouses in the North.
Olive. Picturesque tree with twisted, gnarled trunk and branches as it gets older. Leaves are small, thick and evergreen, olive-green above and silvery below. Slow-growing plants bear black fruits that fall when ripe.
Pacific Madrone. Arbutus menziesi). An attractive broad-leaved evergreen, with fragrant, heathlike, white flowers in six-inch panicles surmounting large, glossy leaves. Chocolate-brown bark sheds like that of the plane tree. Difficult to move, plants are best transplanted as seedlings under eighteen inches.
Palms. Often seen in the North in public parks and botanical gardens in tubs. Graceful with slender trunks, often curving, and arching leaves. Some are small, as the lady palm (Raphis excelsa) which attains six to ten feet. All grow easily and withstand neglect.
Sweet Bay or Grecian Laurel. The true laurel of the ancient Greeks, familiar as a clipped tubbed specimen, often with a single trunk and pungent, dark green leaves. Tough and easy-to-grow, appropriate for formal doorways, hotels, or public buildings. Requires a cool place in winter in the North.
Rubber Plant. A familiar house plant in the North with large glossy leaves. Include some variegated forms for color highlights.
With trees, shrubs are needed for background, mass effects, and shade. Every container garden also requires some hardy needle and broadleaved evergreens for year-round color. In summer in the North, these can be supplemented with camellias, pittosporums, podocarpus, oleanders, sweet bays, and citrus plants. Include deciduous types for bloom and the interest of the branches in winter. Here is a recommended but far from complete list of possibilities.
Arborvitae. Versatile evergreen for the portable garden. Inexpensive, hardy, and quick-growing, it is ideal for hedges or background or for closing off sections. Little Gem, a variety of American arborvitae, is low and compact, a foot high, but spreading several feet.
Azaleas. Brilliant flowering shrubs requiring an acid soil. They also make good container plants in alkaline areas since soil can be prepared for them. Plants take shade, but flower better in sun. Always keep moist, since fibrous roots resent drying out.
Brooms or Cytisus. Green arching stems, with abundant flowers in spring. Require full sun and a light, sandy soil. Both the showy Warminster broom, with yellow flowers, and the familiar golden Scotch broom are dependable.
Cotoneasters. Interesting with a world of possibilities. Flowers are inconspicuous but glossy leaves and colorful berries are attractive. Rock spray cotoneaster has flat, horizontally arching branches. The small-leaved evergreen cotoneaster can be arranged around trees in planters and large boxes to avoid bareness.
Enkianthus. Handsome with small, bell-shaped flowers in pendulous clusters, fine to see close at hand. Lustrous leaves become fiery red in autumn. An acid-soil plant, requiring the same culture as azaleas.
Fothergillas or Bottlebrushes. Small shrubs with white flowers in spring and large, coarse leaves that color in autumn. Dwarf fothergilla (Fothergilla gardeni) attains three feet, but the large fothergilla (F. major) grows taller.
Hollies. Handsome plants, with shiny foliage and bright berries. Japanese holly (Ilex crenata) has dark green leaves; the convex-leaved Japanese holly has small, rounded, highly polished leaves; Haller's Japanese holly is a small, compact variety; and Kingsville is a true dwarf. Inkberry, another shrub holly, has lustrous evergreen leaves, an open habit, and black berries in fall. Leaves turn bronzy-purple in winter.
Japanese Flowering Quinces. Many varieties, including dwarfs with vermilion, scarlet, pink, rose, red, apricot, and white blossoms. These easy shrubs are primarily desired for early spring vivid color.
Japanese Yews. Among the best evergreens for hardiness, ease of culture and tolerance of sun or shade. There are upright, columnar, spreading, and low forms; all have dark green needles and are excellent for contrast with flowers. These are hardy in the North, but be sure to water all container plants in winter when soil is not frozen. The upright, rounded Hatfield and the columnar Hicks yews make good hedges. Where hardy, English yews can be substituted.
Pieris. The upright Japanese has hanging white flower clusters and bronzy-red new spring growth. The mountain pieris is lower and rounded, with upright white flower heads. Both have attractive foliage and are dependable the year-round.
Roses. Many kinds are suited to containers. Floribun-das are more floriferous than hybrid teas and can be used as low hedges or in groups. On terraces and patios include hybrid teas for color, form, and fragrance if you can face the spraying, etc. Where hardiness is questionable, store in a cool place, as a garage or closed-in breezeway, in winter. In pots and window boxes grow the delightful miniatures.
Rhododendrons. Broad, glossy, evergreen leaves and showy flowers in red, rose, pink, purple, or white. Give sun for a few hours a day for richer bloom. In winter, put in a protected spot to avoid windburning. Rhododendrons need a peaty, humusy, acid soil and plenty of water.
Spice Bush. Moisture-loving, with small, yellow, pungent flower clusters in early spring. The leaves unfolding later are large, neat, and aromatic.
Rosemary. Mediterranean shrub with narrow, aromatic leaves that are dark green above and gray-white below. Thrives in sun and slightly dry soil; becomes leggy in shade in rich soil. Plants develop a natural asymmetrical habit, but may be clipped. The variety, Heavenly Blue, has semitrailing branches and small flowers, deeper blue than the species.
Ruscus. Called also butcher's broom, a low-growing evergreen that is a common pot plant in patios of Mediterranean countries. Stiff habit and leathery, prickly, pointed leaves. Rugged plants withstand hot sun, shade, poor soil, and drought.
VINES FOR SCREENING
Vines and climbers perform significant roles in container gardens. They cover walls, fences, and other vertical spaces. Attractive in flower and foliage, they also form interesting patterns, cover unsightly areas, cut off undesirable views, provide screening for privacy, and create shade for plants.
There are hardy and tender vines, depending on where you live. Stephanotis, clerodendron, wax plant, allamanda, poet's jasmine, and bougainvillea are tender in the North.
Hardy vines include English ivy, Virginia creeper, Boston ivy, climbing euonymous and Dutchman's pipe, which are grown for their foliage. For quick one-season effects, there are annual climbers-morning-glories, moon vines, cardinal climber, scarlet runner beans, climbing nasturtiums, cobaeas, and sweet peas.
Wisteria. A most spectacular hardy vine, with long, pendulous clusters in spring in purple, lavender, pink, and white. The Chinese wisteria, which flowers without leaves, is less hardy than the Japanese, which blooms with foliage. Vigorous plants require large containers and constant pruning to encourage bloom and also keep them in hand. Tree wisteria is most decorative when grown in a tub.
Hybrid Clematis. Handsome hardy vines, with large, starlike blooms, in lavender, purple, red, pink, or white in late spring and through the summer. Nurserymen offer hybrids in pots, easy to transfer to larger containers. Provide a well-drained soil with lime added.
Star or Confederate Jasmine. A pot plant in the North, though hardy in the South, with small, star-shaped, pin-wheeled, fragrant flowers that smother the glossy evergreen leaves. Give a large pot or tub and place where the scented flowers can be enjoyed close at hand. Thrives in sun or shade.
Stephanotis. Glossy-leaved, with scented, white, waxy flowers. Not hardy in the North, keep in a cool place in winter and water sparingly.
Allamanda. A tropical vine, with shiny leaves and large, tubular, yellow flowers produced freely all year around. In the North, tender plants require a greenhouse. Vines like sun and rich soil, but are not otherwise difficult.
Bougainvillea. Also called Chinese paper flower, with vibrant, fiery flowers in magenta, purple, rose, pink, red, and white. Not particular as to soil, but needs sun and plenty of water when growing. Rest in cool place in winter by keeping on dry side.
Gloriosa. A tuberous-rooted tender vine, with red and yellow lily-like flowers. Hardy in the South, plants are treated as pot subjects only in the North. For this, start tubers in large pots in March or April and bring to a sunny spot outdoors when freezing weather has passed. Provide trellis support, water regularly, and feed with liquid fertilizer when plants are half grown. Store bulbs in their own pots in a frostproof place and start them again the following spring.
Passion Vine. Odd and beautiful flowers on quick-growing plants that need rich soil and large containers. In the North, this is often treated as an annual, but plants may be kept in a cool room during winter, where they will continue to bloom. The fragrant flowers close at night, but will remain open if melted wax is dripped on the inside. After treatment, flowers make fine corsages or can be floated in bowls of water.