New Choices for Urban Islands
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New Choices for Urban Gary L. Koller Islands Urban islands are meant to be oases of William Flemer III has identified and dis- natural greenery that contrast with and cussed many tough plants m his article in visually soften the hard surfaces of urban this issue. These plants have proved them- landscapes. One wonders if the plants we selves through repeated successful applica- now utilize are tough enough to survive be- tions in urban sites, and they should con- nign neglect, harsh environmental condi- tinue to be used. At the same time we must tions, and vandalism. Some plants are, but continue to seek little-known new plants one sees many urban islands in which the that adapt to island habitats. What is needed plants are dead or dying. A plant that would is the widest possible array of plants to flourish in one location might fail miserably select from, so that we have species fitting m another, and it would be incautious there- every specialized habitat. fore to recommend a plant for all situations. The plants listed below have been selected In any planting it is most important to ob- for toughness, longevity, and adaptability to serve the conditions of the site and choose a wide range of environments. All present plants that most readily adapt to that the primary attribute of attractive foliage habitat. throughout the growing season. Most are lit- It is my opinion that plants are often tle known and little used, and few are com- chosen because of ornamental criteria, such mercially available at present. All are hardy as showy flowers, brilliant autumn foliage at the Arnold Arboretum and can be ob- colors, or evergreen foliage. What is ulti- served there. The list that follows is for mately more important is to select plants nursery growers and landscape architects that are capable of thriving under existing who wish to, dare to, and can afford to exper- site conditions. If the plant does nothing iment with something different. Why not more than provide a green, leafy presence m select one or two for evaluation and help ex- the city, then it has performed well. The im- tend knowledge about plants for urban is- portance of flowers, fruit, and autumn color lands ? should be secondary, for what good is the most gorgeous flowering tree or shrub if it is Trees barely surviving? I also believe that we Asimina triloba (L.) Dunal. Height 5-8 m. should revive the use of tough plants with to -10°F. minor ornamental attributes that have been Hardy Pawpaw. abandoned in favor of prettier plants that are Plantings on many large islands in cities are often more exacting in their habitat re- often visually monotonous because of regu- quirements. larly spaced specimen trees. Thickets or col- 38 39 onies would mcrease interest and create the Chamaecyparis pisifera /Siebold & Zucc.) effect of an urban woodland. Endl. Height 12-21 m. Hardy to -30°F. The pawpaw is a native colomzmg tree Sawara cypress. that spreads outwardly via rootsuckers. Be- is of re- cause shoots arise next to and in the middle Chamaecypams pisifera capable markable under the most difficult of nearby plantings, the pawpaw is best used growth conditions, where many other alone in a mass planting, with a simple surviving fail. In many locations the common ground cover such as Rhus aromatica Ait. plants such as white ’Gro-Low’, Symphoricarpos x chenaultii evergreens, pine (Pinus Rehd. ’Hancock’, Arundinaria viridistriata strobus L.), Canada hemlock (Tsuga canadensis [L.] Austrian pine (Siebold ex Andre) Mak., Aruncus dioicus Carriere), Walt., orXanthorhiza simplicissima Marsh. (Pinus nigra Arnold), and Japanese black Franco/, are The pawpaw has a round-topped shape, pine (Pinus thunbergiana failing Their decline can be attributed to and good specimens bear branches directly miserably. intolerance to drought, air pollution, envi- to the ground. The leaves are 15-30 cm ronmental salts, construction damage, and long, light to medium green, and visually insects or diseases. distinctive because of their pendent or Mature of drooping character. Autumn foliage is an at- specimens Chamaecyparis in tractive amber yellow. The fruit, which is pisifera appear many long-established The trunks are tall edible, resembles a short, fat banana. It rip- inner-city landscapes. and with a cinnamon brown to ens to a purplish brown color and possesses a majestic, distinctive flavor and texture. gray-brown bark. The trees have an openness of habit that a view Although Asimma has few other habitat permits through them, and their yellow-green foliage is attractive in requirements, it prefers a soil that retains the winter mature adequate moisture. It is somewhat difficult landscape. Frequently, possess a fullness of form that to transplant, and nursery-grown specimens plants layered is absent in many pines, spruces, and firs. dug for transplanting are slow to recover Sawara are best in vigor and normal shoot elongation. cypresses planted In one such at the Arnold Container-grown plants may respond more groves. planting Arboretum, mdividual plants are spaced quickly. Once established, the plant is un- the outer branches demanding and long-lived. 6-8 m. apart. Today the space beneath the Pawpaw has many potential uses. It would touch, enclosing look handsome running along a ridge or on canopy. Dwarf cultivars of both sides of a path. It would also be effec- Chamaecyparis pisifera have become more than the tree tive as a leafy camouflage for the concrete popular which are now in slabs that serve as noise-reduction barriers types, infrequently grown along highways. the nursery industry. Perhaps this is because the tree types were used mappropriately m the past. They were often planted beneath windows, next to doorways, and along where their full The Sawara cypress /Chamaecypans pisifera/,[, driveways, qmck, growth foreground. overwhelmed the space. As a result, they 40 were ineptly pruned, creating an ugly effect. horticultural promise is the big-leaf dog- Chamaecyparis pisifera is a plant of wood, which is native to China and Japan. robust, vigorous growth. It is extremely tol- Tom Dilatush, an observant nurseryman erant of dry, nutritionally poor soils, as well and plant collector from Robbmsville, New as the sandy soils of coastal areas. It must be Jersey, tells me that he finds Cornus mac- grown m full sun, as shade kills leaves and rophylla to be more drought tolerant than branches. Sawara cypress is exceptionally other arborescent dogwood species. He also tolerant of winds and ocean spray. Long- says that it transplants more easily and re- established plantings are present on the is- covers more qmckly. lands of Martha’s Vineyard and Nantucket. Dunng early July large quantities of tiny The cultivars of Chamaecypans pisifera creamy white flowers are borne on flat- are numerous, and most are dwarf or com- topped terminal panicles and resemble those pact evergreens. However, several sig- of red-osier dogwood (Cornus semcea L.j. By nificant tree forms are available, including early August clusters of tiny light green fruit _ ’Plumosa’, which is dense and conical with appear against the dark green leaves. As the ascending branches. Mature trees at the Ar- fruit ripens in September, the pedicels turn nold Arboretum planted in 1891 now stand an attractive rose pink, while the frmt ripens 9-12 m tall. Winter foliage color is a brown- to a blue-black color. Birds quickly strip the green, which some consider unattractive. ripe fruit, but the pedicels remain for an- This cultivar could be improved by the other 3-4 weeks. Autumn foliage color is selection of mdividuals with shiny, dark unremarkable. green foliage that remains attractive year- Big-leaf dogwood has a strong tendency to round. ’Squarrosa’ is one of the most distinc- produce multiple trunks rising from near tive evergreens for soft blue-grey foliage and soil level, and in habit it resembles an over- rapid growth. Although the inner foliage grown shrubby dogwood. The mature tree turns brown and dies, it can be removed by has a rounded shape. One of the Arnold Ar- fine pruning. This produces an attractive bil- boretum’s trees has grown from seed re- lowy effect, which is beautiful in combma- ceived in 1951 and today has a spread of tion with the foliage color and texture. 14 m, with four stems rising from just above the soil level to 9 m high. Cornus macrophylla Wallich. Height 8- Another specimen thrives in rich, moist 11 m. Hardy to -10°F. Big-leaf dogwood. soil in full sun. It grew from cuttings in 1980 and was transplanted to the grounds in Our native and dogwood /Cornus florida L.) spring 1982. By August 1, 1984, the new sea- the kousa kousa con- dogwood (C. Hance) son’s growth averaged 30 cm, and the plant tinue to be on with various planted islands, was approximately 3 m tall. degrees of success. Many fail because they have been planted too deeply. Drought Corylus colurna L. Height 9-15 m. Hardy to stress, salt reflected heat and sun- damage, -20F. Turkish filbert. light, or mechanical damage to the stem or root system are other causes of failure. Turkish filbert is now rare in street or island One relatively unknown dogwood with plantings, but I am certain that it will be 41 more widely used once it becomes better in superb condition until autumn, when known. Two factors offer promise for in- they turn to yellow or pale gold. creased use. First, the filbert canopy is more At the Arnold Arboretum we have lifted open than that of most moderate-sized trees several old plantings, divided off clumps, because of this tree’s wide-angle branch and reestablished colonies at new planting formation.