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. Second, when the filbert becomes sites. The bare-rooted transplants in some established, it adapts to and conditions and cases were slow in becoming established but exposed sites. eventually developed a physical density and Foliage rs a rich, dark green throughout luxuriant appearance possessed by few other summer and fall. Pendent staminate catkins plants. Sweet shrub is singularly appropriate are present in a reduced size throughout the for creating mass plantings m either sun or winter but grow and enlarge to a length of 5 shade. To maintain the richness of the to 8 cm as the weather warms in spring. Late foliage, the plants require shearing to soil each summer a nutlike fruit appears, sur- level every five to six years. rounded by a curiously fringed light green Flowers are purplish brown and not par- involucre. Although not showy, the fruit is ticularly eyecatching but have a delightful visually interesting. Squirrels quickly carry spicy fragrance. The fragrant character varies away ripening seeds, so no litter remains. enormously among plants produced from The light brown filbert bark is distinctive, seed. Some nurseries have selected and vege- with small scales that flake off, revealing tatively reproduced forms with outstanding patches of pale orange-brown. fragrance, while others continue to produce I have observed long-established Turkish inferior lines. One would hope that nurseries filberts at the Arnold Arboretum, Mt. Au- would evaluate and then purge their line of burn Cemetery in Cambridge, Massachu- propagation stock with poor fragrance. setts, the Brooklyn Botanic Garden in New York, Temple University in Ambler, and in Pennsylvania, Cornell University Colutea x media Willd. Height 2 to 3 m. York. At all locations the trees Ithaca, New Hardy to - 10°F. Bladder senna. displayed beauty of form, crisp foliage, and Bladder senna is overlooked as a medium- freedom from insect and disease pests. sized shrub of in full sun on Corylus colurna offers the promise of a capable thriving infertile soils. In fact, it will completely new tree to widen species diver- dry, gravely, colonize sites too for sity in islands and other difficult urban loca- inhospitable many tions. plants and is therefore the most appropriate choice for restoring the banks of fresh high- way cuts. It is also useful in planting islands Shrubs and semiwild urban parklands. Colutea x media is a hybrid of Colutea Calycanthus flondus L. Height 2-3 m. arborescens L. of southern Europe and C. to -15°F. Sweet shrub. Hardy orientalis Miller of Asia. At the Arnold Ar- Outstanding foliage is this plant’s chief as- boretum peak flowering occurs in mid-May, set. The leaves remain lush, dark green, and with scattered blossoms appearing through- 42

out the summer. Flowers are pea-shaped and formed a dense, impenetrable barrier, which usually butter yellow, but some have mark- guided pedestrian traffic. The foliage was ings or tints of copper, pink, or reddish dark green and lush. Russell Myers, director brown. Flowers are followed by large, thin- of parks for the state of New Jersey, told me walled, inflated pods that may be lime green that he considers Diervilla one of the most or richly tinted with pinks and bronze. The reliable plants for mass and ground-cover seed pods are highly ornamental from June plantings on the banks of highways. John through late July, when they begin to ripen Trexler, former horticulturist at the Freling- and turn straw brown. The ornamental qual- huysen Arboretum, has noted that deer ities of these inflated pods rival those of browse the foliage during late summer, a fac- many flowering shrubs. tor that must be considered in planting in Bladder senna is generally rounded in rural situations. habit. The foliage is sparse and the branch- I often walk along the Marginal Way in ing is open - some might say rangy and un- York Harbor, Maine, where Diervilla loni- - kempt. The shrub is least attractive in late cera Mill. grows on the dry rocky soils of the summer, when the seed pods turn brown and cliffs, exposed to the winds and the salt the leaves lose their color. It looks best when spray from the Atlantic Ocean. This species grown in a low ground cover, such as Sym- is less handsome m leaf thanD. sessilifoh a, phoricarpos x chenaultm ’Hancock’ or and it is said to be slightly less vigorous in Aegopodium podagraria L. ’Variegatum’. growth. However, its tenacity under harsh environmental conditions is indicative of the of the Diervilla sess111folia Buckl. Height 1-2 m. vitality genus. Hardy to -20°F. Southern bush hon- Diervilla can be cut to soil level each au- eysuckle. tumn, and snow and ice can be disposed of on the space occupied by the roots. Damage Diervilla is an ideal tall, woody ground or harm to the plantmg itself is unlikely. cover, for it forms dense, multistemmed Once well-established, the plants grow and thickets and is easily propagated and trans- thicken rapidly each spring. Flowers are At the Arboretum in planted. Frelinghuysen borne on the wood of the new season and so Morristown, New Jersey, the staff maintains are unaffected by the pruning. The flowers two large colonies in stock beds to provide are yellow and appear in midsummer. Still for use in Morris County parks. When plants later the purple-bronze foliage enhances the plants are needed, staff members cut back muted color spectrum of the autumn land- the tops and remove root clumps from the scape. bed. After removal, the digging holes are backfilled and the area fertilized. The colony Hamamells vmgimana L. Height 5-8 m. then renews itself from the root pieces re- Hardy to -20°F. Virginia witch hazel. maining in the soil. Within a season or two, the bed is ready for removal of another crop. During the months of October and Novem- When I last visited the Frelinghuysen Ar- ber, the Virginia witch hazel blooms at the boretum m 1983, the mature bed stood ap- edges of woods and in clearings along proximately 1 to 2 m tall, perhaps 18 to 24 m streams in Massachusetts. Some of the flow- across, and 8 to 9 m wide. The planting ers are obscured by withered leaves, but 43

overall the effect of the pale yellow to bright tall and spreading 1-2 m across. It has a gold flowers is quite stunning. superb emerald green summer color plus a Accordmg to Geraldme Weinstein, direc- surface texture resultmg from pendent tor of horticulture for the New York De- branch tips. Branches pile up on top of one partment of Parks and Recreation, the Vir- another, and lower ones retam foliage only ginia witch hazel transplants easily and even where they extend beyond the shading without maintenance generally survives canopy. Plants grow well m full sun to mod- heat and drought after transplanting. Few erate shade. In winter shade is necessary to shrubs cling so vigorously to life during the prevent them from turning brown. Mac- period immediately after transplanting, and robiota thrives in acid or alkaline soils and few resume normal shoot elongation as grows best in well-drained sites. quickly. This shrub is one of the most suc- Better forms of this plant need to be devel- cessful in Central Park, despite a high level oped for the winter landscape, and when of environmental stress. seeds become available progeny testing At the Arnold Arboretum we have several ought to be performed. Once improvements witch hazels approaching their centenmal are made, I am sure microbiota will become year, and during a midsummer inspection a substitute for junipers along the edges of is- they looked robust enough to last another lands. This plant is also suitable for interior 100 years. One plant, which stands alone planters m shopping malls; I am told that it near the Centre Street gate, is approximately has performed well in limited trials. 5 m tall and 12 m across. It forms a dense wall and is graced by branches that brush the Rhodotypos scandens (Thunb.) Mak. Height at the In another location three ground tips. 1-2 m. Hardy to -20°F. Jetbead. plants spaced approximately 3 m apart give is a and that the appearance of a single plant with a Jetbead compact rugged plant looks attrative for with a mini- spread of 17 m. In a third location the witch many years mum of maintenance. With its limited hazel grows in a natural-looking thicket and and dense it forms with native dogwood and Carolina silver- height spread crown, bell. On all Arboretum plants the oldest an ideal background for taller and more leggy such as leaves are a dark green; younger leaves are shrubs, beautybush (Kolkwitzia amabihs or lilac light green; and the youngest are green Graebn.) (Synnga vulgams sees used as a tinged with shades of purple or bronze. Au- L.). One occasionally jetbead but it is at its finest when al- tumn color is an attractive clear yellow. Be- clipped hedge, lowed to and in- cause of it stature, Virginia witch hazel is grow naturally relatively with a or textured suitable only for islands over 8 m m diame- formally layered foliage ter. surface. Many small white flowers appear among the leaves during mid-May to early June. Microbiota decussata Komar. 30- Height Later, shmy black fruits, resembling small 60 cm. Hardy to -25°F. Microbiota. peas, occur in groups of three or four. The Microbiota, which has the appearance of a summer foliage is light green, and its attrac- prostrate juniper, is a rapid grower. In three tiveness is enhanced by a strongly mdented to four years it forms a dense mat 30-60 cm vein pattern and doubly serrate leaf margin. 44

Autumn color ranges from yellow-green to was reproduced vegetatively and is therefore amber-yellow. I have been enchanted by the more predictable in its mature habit. mellow color effect of a hedge in autumn at Because of its short stature, broad spread Cornell University. (1 to 2 m across), and adaptability to either Jetbead resists insects and diseases, toler- full sun or moderate shade, this plant is an ates drought and salt spray, and thrives m ideal substratum or ground cover. Its yel- both moderate shade and full sun. It also lowish flowers, which appear m early spring, transplants easily and reestablishes itself are mconspicuous. Its autumn foliage color, quickly. Plantings in inner-city locations in shades of reddish purple to yellow-orange, thrive many years after mstallation. is a more ornamental feature of this plant. Jetbead’s ornamental characteristics could This is an ideal species for islands with shal- be improved by selection. I am unaware of low, dry soils. any existing selections and would welcome news of that are available. Most any plant- Rhus chinensis. Mill. Height 5-6 m. in the United States represent vegeta- - -- ings Hardy to -10°F. Chinese sumac. tive propagations from limited parental ma- terials. We need to make more introductions The landscapes of late August and early from the full range of this plant’s native September are considerably enhanced by the habitat. Desirable characteristics mclude rich golden yellow flowers of Koelreuteria the more abundant and larger flowers and a pamculata ’September’ and creamy more compact size when mature. I have re- white flowers of Rhus chinensis, the two most trees of this season. quested that a fall 1984 National Arboretum showy flowering expedition to Korea seek variants of Chinese sumac produces large, open cone- Rhodotypos. shaped terminal panicles 20- 25 cm tall. Although it could benefit from selection, Flowers last 10-14 days and then give way which turn this is presently a more dependable and dur- to clusters of small bony fruit, able plant than many shrubs that are now orange when mature. As flower and fruiting from to more commonly employed in the landscape. qualities vary significantly seedling seedling, breeders are attempting to develop improved selections. Dr. Elwin Orton, of Rhus aromatica Ait. ’Gro-Low’. Height Rutgers University, submitted one selection the 37 cm. Hardy to -30°F. ’Gro-Low’ fragrant called ’September Beauty’ to Pennsyl- to be tested and sumac. vania Horticultural Society evaluated for the Styer Award. This award Fragrant sumac has already established its recognizes plants with exceptional orna- usefulness as a tall woody ground cover mental characteristics. along highways, where one can see it grow- The dark green leaves of Chinese sumac ing on embankments and along the bases of are handsome all summer long. The promi- bridge abutments. When grown from seed, nent marginal tooth pattern and the winged Rhus aromatica can be quite variable in leaf-rachis are also attractive. Autumn color height, density, vigor, and area of spread. can be bright orange or scarlet or rather drab, ’Gro-Low’ fragrant sumac is a selection that depending on weather conditions. 45

chmensis as a commercial landscape plant are the nursery industry’s view of native sumacs as having little ornamental value and the public misconception that these plants are poisonous. Although many plants have greater ornamental value, few match the Chinese sumac for late season bloom and for toughness in those difficult envi- ronments we call urban islands.

Sinarundmaria murielae (Gamble) Nakai. Height 1-3 m. Hardy to -10°F. This bamboo, whose name has been the source of much confusion, was acquired by the Arnold Arboretum from the U. S. De- Chinese sumac (Rhus chmensis /. partment of Agriculture Plant Introduction Station m Glenn Dale, Maryland, in No- vember 1960 It Chinese sumac is variable in growth and (P.I. 262266). rarely appeared outside botamcal until habit. With pruning, it can be mamtamed as gardens recently, when the architectural team of a single-stemmed specimen tree. However, landscape Oehme and A. van Sweden it tends to sucker from the root system, and Wolfgang James its and as a result it is best used in multiple-plant recognized undeveloped potential its use. colomes or thickets on large islands. Cutting promoted the whole colony to the soil level every When I arrived at the Arnold Arboretum, fourth or fifth year just before new growth over eight years ago, a magnificent specimen begins will keep the colony lush and vigor- grew in the shrub collection in Jamaica ous and in prime flowering condition. Plain, and another of equal merit grew in the At the Arnold Arboretum several Chinese perennial garden at the Case Estates m Wes- sumacs grow m full sun and one in shade. ton, Massachusetts. Although these plants The shaded specimen, which was received in have since been removed as a source of prop- 1952 and now stands 6 m tall, produces agating stock, I remember that they stood flowers but not so many as those in full sun. 2 m tall and spread in dense clumps (2-3 m It also lacks significant autumn color. This across). They had a graceful arching habit sumac’s adaptability to nutritionally im- and small and delicate foliage. Unfortu- poverished dry, sandy soils renders it an nately, when the Arboretum’s long- ideal plant for islands and parking areas at established clumps were lifted as a source of summer resorts, where its late-summer divisions to increase the stock on hand, 98 flowering would be especially appropriate. percent of the young plants were lost. The plant does require well-drained soil, Richard A. Simon, manager of Bluemount however. Nurseries, Inc., of Monkton, Maryland, has Factors that hamper development of Rhus reported similar difficulties m trying to in- 46

crease this bamboo. Development of this fill in and unify a mixed shrub and tree plant on a commercial basis will be hamp- border. It can also be used as an underplant- ered until better methods of propagation ing for a grove or group of trees. Landscape are discovered. However, once it has become designers must exercise care in choosing established it clumps up rapidly and again companion plants, for Sorbaria will domi- becomes tough and dependable. At present nate smaller or slower-growing plants. we have a superb colony of four plants that Close inspection reveals luxurious, light were grown from divisions and planted in green leaves, which are pinnately com- June 1981. The plants were spaced 1 m apart pound. Individual leaflets are marked by the in a square pattern. By August 1984 the veins and bear bold serrations on the leaf combined clumps appeared as one plant, margm, similar to those of European moun- which stands 2 m tall and spreads 3 m tain ash (Sorbus aucuparia L.). Under opti- across. The planting is extremely dense, mal conditions the foliage remains crisp and with upright central stems and arching outer attractive throughout the summer. When

- canes. The plants often remain green until the plant lacks water, however, the leaves January, but by spring the persistent foliage lose their freshness by late summer and turn is bleached to a tan color. I am told that in yellowish brown. Pruning and fertilizing the Washington, D.C., the plants are more reli- plants in spring, as well as supplemental ably evergreen, but they do best with wind watering, will help to prevent this. protection and shade to shield them from Terminal racemes of small creamy white late afternoon sun. New growth, which be- flowers appear in late June to early July. The gms late, arises from basal culms and floral cluster can vary from short and slim to branches. Once established Sinarundinaria broad and bushy. The flowers resemble munelae is a plant of distinctive habit and those of Astilbe but are much larger. Since reliability, with minimal mamtenance flowers develop over several weeks, fruit and needs. flowers are sometimes present together. The ripening fruit capsules are tan and brown and a discreet of color with Sorbaria sorbifolia L. provide montage (A. Braun). Height the white flowers. 1-3 m. Hardy to -40°F. Ural false spirea. Sorbaria sorbifolia roots readily from cut- On islands where a dense, multistemmed tings and as a result is generally propagated shrub is required, Sorbana would be the first vegetatively. This factor, combined with the choice. This plant can spread to a much fact that the plant is so infrequently grown, greater width than its mature height, and the has meant that no selections or horticul- habit varies considerably, from a low con- turally improved forms are available. A plant toured mound in dry locations to a taller selector might seek larger flowers, fuller more blocky shape on fertile or well-watered racemes, or a more compressed flowering sites. The plant’s stolomferous growth re- cycle in which all the floral clusters would quires that one use it where it can be re- appear at approximately the same time. strained by barriers such as walkways, walls, or curbs. Sorbaria is a superb selection where a natural look is called for, as it will Flowers of Ural false spirea (Sorbana sorbifoha).[. 47 48

Forms that remain compact would also be for it mtertwmes with itself to form a con- desirable. Sorbaria grandiflora is a smaller tinuous carpet. Used to unify a planting of shrub than S. sorbi foha, with a mature Taxus or Euonymus alata, it would provide height of 1 m or less and larger flowers. Ac- a more immediate finished look to the total cording to the Plant Science Data Center, plantmg. the Arnold Arboretum has the only rep- The flowers are pinkish, and the green resentatives of this species in the United leaves are tinged with shades of reddish States. Our plants were obtained as seed orange and gold in spring and summer. In from Domaine des Barres, Nogent-sur- fall, foliage exhibits a rich mosaic of colors. Vernisson, Loiret, France, in April 1939. In late July they were 1 m tall, with full-bodied Tripterygmm regelii T. Sprague & Takeda. flowers. Height 5-8 m. Hardy to -20°F. Sorbaria is tolerant of salt spray and oc- is a scandent shrub that exhib- cupies the same habitats as Rosa rugosa Tripterygmm its all the of its bit- Thunb., dry, rocky slopes facing the sea. toughness relative, tersweet scandens When it Because of its size and spread, it is not suit- (Celastrus L./. stands its branches to able for islands smaller than 4 m in diame- alone, grow upward 2 m and ter. It can be used to create a mound or de- approximately then arch outward. Their and the stems sign contour on sites where budget lim- length weight pull downward so that the outer branches arch to itations preclude moving soil to mampulate the grade. the ground, creating a skmtlike effect. Next to another plant, a trellis, or a chamlink fence, Tripterygmm will twist about the Spiraea x bumalda ’Gold Flame’. Height 1 support as a vine. It can be used to cover ugly m. Hardy to -30°F. ’Gold Flame’ spirea. fencing, for the vegetation will provide a Japanese and bumald spirea are compact, leafy screen that can be managed by occa- hardy, long-lived, and troublefree. They also sional shearing to control growth. One cau- have the advantage of an early-to- tion : Tnpterygmm should not be grown on midsummer flowering period. Spireas can be supports near walkways, for branches that used en masse as a woody ground cover to extend outward will interfere with pedes- unify plantmgs of larger shrubs such as trian traffic. The variable growth habit of rhododendron, forsythia, or winged this plant presents some difficulty when euonymus. These taller shrubs are often Tripterygium is grown with other plantings, planted to create the effect of a thicket but for it becomes entangled with and overgrows do not do so for many years. In the interim a shrubs and small trees. It is most appropriate mass planting of Spiraea x bumalda could on islands with rocky outcroppings or land- be used to fill the empty spaces and unify the scape mounds that it could cascade over. It is plantings. While they may ultimately be- also suitable for highway median strips and come crowded out, spireas will cling to any ideal as a means of masking the cast- and all niches that remain favorable for their concrete units known as Jersey barriers, growth. Spiraea x bumalda ’Gold Flame’ is which are increasingly seen along highways. one of the best cultivars for mass plantings, Dense terminal panicles of small creamy 49

and grew a large seedling population to es- tablish a mass plantmg along Willow Path. Four-year-old seedlings bloomed freely. Mature plantings form a short thicket of stems that surround and face down neigh- boring plants. Flowering in yellow-root is rather insigmficant, for blossoms are tmy, brown-purple, and appear before the foliage m late April. Casual observers can walk past a colony in full bloom and not notice the flowers. The foliage stays green later in the season than that of most deciduous plants and rarely colors before November, at the same time as or slightly after the oaks. Ar- boretum plantmgs turn a bright amber yel- low, and a mass planting makes a strong visual impact, mainly because the color ap- pears when other yellows have long smce passed. Yellow-root is ideal massed around taller shrubs, such as Calycanthus floridus L., Rhododendron vaseyi A. Gray, or R. calen- dulaceum Vaccmum Tnpterygmm regelii. Michx., corymbosum L., orPhiladelphus spp. In marginally swampy soils it combines with Magnoha white flowers are this plant’s chief ornamen- Clethra and Ilex tal quality and reach their peak m late June mrginiana L., alnifolia L., verticillata ~L.) A. Gray. or early July. The flowers are followed by Yellow-root must be mowed to the three-angled, conspicuously winged fruits, ground occasionally in order to mamtain density. which at first are lime green and then ripen Otherwise, it thrives with little care or at- to light brown. tention and is therefore a first choice for urban islands. Xanthorhiza simplicissima Marsh. Height 60-90 cm. Hardy to -30°F. Yellow-root. Although yellow-root lacks the refinement Herbaceous Perennials of many cultivated plants, it is ideal for Arundinaria vmdistriata (Siebold ex Miq.) naturalistic groupings. It is extremely flexi- Mak. Height 1 m. Hardy to -15°F. Golden ble in its habitat requirements, growing in stripe bamboo. full sun or moderate shade and in wet or dry soils. This colorful bamboo has been growing at At the Arnold Arboretum we collected the Arnold Arboretum since the early 1900s seed from a planting at Garden m the Woods and is noted for its exceptional hardiness, 50

Shrub yellow-root /Xanthorhiza simplicissima)./. in islands with granite or concrete curbs, as it may penetrate asphalt and colonize adja- rampant vigor, and dense canopy. Its green- cent grass areas. Compamon plants must be striped golden foliage is attractive through- large shrubs or trees that rise above the out the summer. The foliage is especially at- bamboo and have a competitive advantage tractive when back lit by the evening sun, because of size, as this plant will dominate which tends to intensify the color and gives low or slow-growing neighbors. the plant a golden glow. The leaves shimmer The golden stripe bamboo is especially at- in the breeze. The plant is at its best in full tractive when grown in front of a New En- sun. It grows successfully in shade, but the gland stone wall or when used in large leaves turn to muted shades of gold or green. masses. Successful plantings I have observed Arundinana viridistriata is extremely m- include a ground cover of Arundmaria vasive and it must be contained. In my own crowned with the golden foliage of an indi- garden it sends out underground stems that vidual or grove planting of Chamaecyparis grow outward at the rate of 1 to 2 m each sea- obtusa (Siebold & Zucc.) Endl.’Crippsii’, son. Perhaps this intrusive vigor is what is which provides contrast in color, texture, needed on island plantings, and what better and mass as well as permanence in the containment exists than a traffic or parking winter landscape. Another possibility is in- island? This bamboo should be grown only dividual plants or drifts of Miscanthus 51

sinensis ’Variegata’ interplanted with a mass branches, which can be used to soften the of the bamboo. The Miscanthus, with leaves edges of islands. striped white, exceeds the height of the The ovate leaves are green, with broad sil- bamboo by half a meter and provides a per- very markings over approximately 1/a to 1/z of manent Victorian bedding effect. Used the leaf surface. These silver markings are alone, this bamboo will form a solid, dense useful in helping to brighten shaded situa- stand capable of restraining all but the tions. The foliage is tough and remains green toughest woody weeds. and in fair condition in Boston until No- Once the bamboo is subjected to a killing vember or December. frost, the foliage turns a tan color. Early Pierre Bennerup of Sunny Border Nurser- winter ice, sleet, and snow often cause it to ies in Kensington, Connecticut, grows yel- break or lodge over and become untidy. low archangel beneath a colony of mature When this occurs, it can be mowed to the maple trees, and the perennial is both full ground, creating space for the disposal of and successful. It will grow in full sun, and I snow without fear of injury to permanent recently saw fully exposed plantings on plantmgs. This seasonal mowing would also Nantucket, Massachusetts. The leaves were help to retard or elimmate the encroach- yellowish, however, and lacked the crisp at- ment of woody plant invaders. tractiveness I normally associate with the After transplanting, bare-root clumps re- foliage of this plant. quire two to three years to resume normal Perenmal companion plants that grow growth, but this recovery time should be through a ground cover of Lamiastrum m- much shorter when container-grown nur- clude common bleeding heart (Dicentra sery stock is used. In order to keep a land- spectabilis [L.] Lem.), Solomon’s seal scape planting dense, it should be top (Polygonatum commutatum [Schult. f.]) A. dressed with a high mtrogen fertilizer at the Dietr., bugbane (Cimicifuga racemosa [L.] beginmng of each growing season. Nutt.) turtle head (Chelone lyomi Pursh.),[, common peony (Paeonia lactiflora Pall.),[, and gas plant ~Dictamnus albus L.~.[. Lamiastrum galeobdolan ~L.~ Ehrend. & The only special care yellow archangel re- is occasional summer Polatsch. ’Variegatum’. Height 30-46 cm. quires pruning during Hardy to -10°F. Yellow archangel. to restram growth. If planted in or near natural woodlands, it tends to become inva- Yellow is a that toler- archangel perennial sive and may overgrow native vegetation. ates both dense shade and dry, impoverished soils. It blooms in early May on erect stems Miscanthus sinensis Anderss. 46-60 cm tall. The flowers are small and Height 1-2 m. to -30°F. Eulalia bright yellow, typical of the mint family, Hardy grass, Chinese silver and partially hidden by the leafy stems. grass. After flowering, which generally lasts 2-3 Decorative ornamental grasses are still rare weeks, trailing vmy stems emerge and root in New England gardens. One lovely, hardy vigorously where leaf nodes touch the soil. species is Miscanthus smensis, which is The stems eventually form a solid mat of available in several useful and distinctive 52

cultivars that vary in habit, height, leaf tex- at the base, and as a result the stems and ture, and foliage colors. During October this habit are more upright. plant bears showy fan-shaped pamcles of One cultivar formerly incorrectly iden- gray to purplish flowers, and these mature to tified as Miscanthus sacchariflorus (Maxim./ a tan color and remain throughout the Hack. ’Gigantea’ is now known as Miscan- wmter. Although not invasive, it can seed it- thus floridulus. It forms a massive clump self into adjacent areas. An example of an es- and spreads by stolons, so its outward caped planting can be seen in a stretch of the growth needs to be planned for or restrained. Pennsylvania Turnpike several miles west of It is useful for accent or as a hedge or screen. the Valley Forge mterchange. Given a few years to establish itself, it has Miscanthus sinensis can be used either the capacity to form a dense solid wall for as a specimen plant or in mass plantings or most of its full height, providing privacy that hedges. It provides the same substance and shrubs require many years to produce. permanent effect as a shrub. When Miscan- All of the Miscanthus mentioned here are thus becomes dormant in winter, the foliage tough, hardy, and long-lived and require lit- turns to colors of tan and beige, and this tle maintenance. Cutting back once each combined with the foliage texture provides year is sufficient. They are generally well an ornamental effect as trees and shrubs lose behaved in the landscape and with a little their leaves. Winter storms tend to cause the foresight and planning will not overwhelm tall stems to break and with time give the their neighbors. a more disheveled In plant progressively ap- ~ York, Pennsylvania, and Baltimore, pearance. When this happens, it should be Maryland, I have seen Miscanthus used suc- pruned to just above soil level. cessfully in the parking lots of fast-food To thrive Miscanthus requires full sun, for restaurants, where ease of maintenance is a in shade the stems are weak and often break. high priority. The grass was mixed among It adapts to many soils, however, from acid trees and shrubs in narrow planting islands. to alkaline and from quite dry to wet. A word of caution: care must be taken to Worthy cultivars include ’Gracillimus’, avoid confusing Miscanthus with weeds ’Variegatus’, and ’Zebrinus’. ’Gracillimus’ early in the spring, when it is difficult to dis- has leaves 1 to 2 m tall that are shiny, dark tinguish from invading grasses. green, upright, and extremely thin, with a texture unlike those of any other Miscan- thus species or cultivar. This cultivar forms clumps easily. ’Variegatus’ is I to 2 m tall. Petasites x hybrida. Mill. Height I m. Its foliage is variegated with white to Hardy to -25 °F. Butterbur. cream-colored stripes running the length of the leaves. In habit it is fountainlike, with Butterbur is a plant whose size and vigor the outer leaves drooping downward. ’Ze- often intimidate designers. It forms a mas- brinus’ is 2 m tall. Its leaves are green with sive colony with a bold tropical effect. Indi- horizontal bars of yellow. This plant is vir- vidual leaves are huge (60-90 cm wide) and tually identical to ’Strictus’ but much fuller architecturally distinctive because of the 53

and full sun to light shade. It tolerates full sun in dry soils, but without adequate mois- ture the leaves wilt during the heat of the day. Even with adequate moisture, the hot- test summer days may cause foliage to wilt. Although invasive, this plant is easily con- tamed by an in-ground soil barner such as a curb. Butterbur can be seen in a number of Mas- sachusetts landscapes, for it was once used as a logo by the landscape architect Fletcher Steele. One of the finest remaining examples of Steele’s work is a public planting at Naumkeag in Stockbridge, Massachusetts. The most elegant planting combination I know is at the Arnold where a Eulaha grass (Miscanthus ~lomdulus/[ Arboretum, vast patch of Petasites surrounds a lovely specimen of dawn redwood (Metasequoia way the petiole joins the center of the un- glyptostroboides H. H. Hu & Cheng) with dersurface of the leaf. delicate fernlike foliage. Butterbur is m the daisy family, and the flowers are among the earliest to appear each Phalaris arundinacea. L. var. picta L. Height spring. They occur in great numbers m 1-2 m. Hardy to -30°F. Ribbon grass. rounded cones that rise only a few centime- ters above the soil surface. A casual observer Ribbon grass is an exceptionally decora- can mistake the greenish yellow flowers for tive plant, with multiple cream-colored early leaf growth. Petasites japonicus stripes that run longitudinally against a (Siebold & Zucc.) Maxim., a relative, is background of green. Dense, stoloniferous, much more dramatic in flower, producing and vigorous, it will quickly invade neigh- tall spikes of rose pink flowers later in the boring plantings unless restrained by a bar- spring. Unfortunately, this species is not rier. It is most useful as a ground cover successful as a large-area ground cover, for planted under complementary shrubs and mdividual stalks are widely scattered, and as trees. a result the plant is not effective as a mass. New growth on ribbon grass begins early At the Arnold Arboretum both types grow at in spring, and the plant reaches mature different sites between Willow Path and height quickly. The leaves remain in prime Goldsmith Brook and are the subject of condition until midsummer. Thereafter, much attention and inquiry from visitors. the heat and drought of New England sum- Petasites x hybrida is rampant and mers cause the foliage to become yellow- spreads across even larger areas each season. brown, especially at the bases of the stems. Its growth is hastened by moist to wet soil Also, strong winds and heavy rains can break 54

the bulbs divide and increase, producing a multitude of smaller but more charmmg flowers scattered through a sea of striped grass. The leaves of both the narcissus and the tulips ripen off before I mow the grass m midsummer, so the bulbs are not disturbed.

Vines Campsis radicans. (L.) Seem. ex Bur. Height 9-12 m. Hardy to -20°F. Trumpet vine.

Islands are often too small or narrow to allow trees and shrubs to grow successfully. For these confined spaces I propose a novel Ribbon arundmacea var. /. grass (Phalaris picta use of the trumpet vine. Upnght supports, such as slender concrete columns, wood posts, or light standards could be installed the stems. At this point, the planting should individually or in groups as supports. Trum- be cut or mowed back to soil level, the area pet vine can be planted at the base of each watered well, and a liquid fertilizer high in support, and using rootlike holdfasts to nitrogen applied. In three to four weeks the cling, it will grow upward. As the vine grass will recover, return to its normal reaches the top of each support, it will pro- height, and remain vigorous until frost kills duce branches that spread outward, resem- the foliage. bling the crown of a small tree. Rigid hori- The habitat requirements of ribbon grass zontal arms installed at the top of each col- are easily met. The plant is best grown in umn will increase the spread. Also, loops of full sun; it will tolerate light shade but will heavy architectural chain, ropes, or cable not reach its full potential there. strung between supports can be used to The species grows wild at the Arnold Ar- create a garland effect. boretum in wet or poorly drained soils. In Trumpet vine flowers in July and August my garden the variegated variety has grown in colors of orange, scarlet, or yellow. The for seven years in dry, sandy soil where it is extra large orange-red flowers of Campsis baked by the summer sun and heat from an xtagliabunna (Vis.) Rehd. ’Mme Galen’ pro- adjacent brick wall. Under the maintenance vide a spectacular complement. regimen discussed above, it remains lush I have selected Campsis radicans over and healthy. other vines because of its ease of culture I have found Phalans to be a good compan- even in difficult inner-city environments, ion for early spring bulbs such as narcissus quick recovery from transplanting or prun- and the large-flowered hybrid tulips. When ing, long life, and ability to recover from re- first planted, the tulips exhibit the large peated attacks of vandalism. blossoms illustrated m bulb but catalogues, Gary L Koller is managmg horticulturist at the Arnold over the years the flower size diminishes and Arboretum