Island and Median-Strip William Flemer III Planting

A generation ago the use of plantings to di- More and more local planning boards there- vide highways or regulate the flow of fore are requiring islands of trees to provide on was rare, confined to wealthy resi- shade and add visual appeal to these other- dential areas in such cities as Philadelphia, wise unsightly spaces. Merchants, too, find Richmond, and Boston, to cite a few well- that although the islands reduce parking known examples. The parkways of space somewhat, they are more effective Westchester County, New York, and Con- than painted lines on the pavement in keep- necticut, as well as the Shirley ing automobiles aligned. Thus, improved along the Potomac River, were among the utilization of space compensates for the loss. first divided roadways with planted strips In selecting trees and shrubs for islands or between them. The plantings were meant to median strips, one must be aware of the spe- create restful driving conditions and to cial difficulties that such sites impose. Nar- screen out headlight glare at night. After row median strips are especially difficult for World War II, planting began on a trees and shrubs because of wind whip from nationwide scale when the huge network of speeding traffic. On highways especially, the so-called national defense highway sys- with cars and trucks speeding by at 60 miles tem was installed. Almost all of the per hour, the wind damage to foliage can be superhighways had separated roadways for severe, both in the spring when the leaves opposing of traffic, and in all but the are soft and tender and in the summer when most congested urban areas the strips be- weather is hot and dry. For this reason plants tween the roadways were planted with trees with tough, thick leaves are most successful. and shrubs. Carefully kept accident-rate In the colder parts of the United States and statistics for old-fashioned and divided- (zone 6 and below), salting in highways proved beyond a doubt that the winter presents additional difficulties. benefits for median-strip planting far ex- Speeding traffic can create a salt spray as ceeded the costs of installation and mainte- concentrated as ocean spray. The salt settles nance. on plants and soil, and prevailing winds de- Now the use of island plantings has begun posit large concentrations on the downwind to spread to other sites. Among these are the side of roadways. It is essential, therefore, parking areas surrounding modern suburban that trees and shrubs chosen for these areas shopping centers. These expanses of pave- are salt tolerant. It is no coincidence that ment become unbearably hot in the summer tree species that thrive at the seashore are months, and locked cars quickly reach oven also successful in island plantings. Thus temperatures during the daylight hours. sugar maple, which is one of the choice 155

species for residential surburban planting in and shade tolerant when young. Climax its native range, is a poor choice for island species ultimately comprise the entire forest or median-strip planting, while sycamore except on very exposed sites. maple does well. Canada hemlock, The ecological conditions of island plant- which is also exceptionally susceptible to ings on highways are extremely harsh for salt spray, should be avoided, while green tree growth, and only pioneer species or ash and Japanese black pine (where it is species from dry, inhospitable climates can wmter hardy) are sound choices. Indeed the be expected to grow well. Island sites are ex- sugar maple decline m New England, about posed to full sun and wind, as well as the which so much was written 20 years ago, has turbulence caused by vehicular traffic. They since been attributed to salt kill. Mamte- are also narrow, so that natural penetration nance crews tend to use salt with a lavish of rain to the root zone is inhibited. It is es- hand, a practice that ought to be vigorously sential therefore to plant only those species curbed. Meanwhile, salt-sensitive species that are tolerant of dry soil. Among the must be avoided m island plantmgs for cold many species of small maples, the Japanese areas. maple (Acer palmatum Thunb.), which is Salt injury to trees in island plantings in strictly an understory tree in the woodlands parking lots can be very serious even though of Japan, qmckly succumbs in island plant- traffic is too slow to create salt spray. Here mgs. The Amur maple (Acer glnnala salt is spread on the pavement, and often be- Maxim.), in contrast, thrives under condi- fore the snow is melted the salt and snow tions that are lethal to the Japanese tree. Not mixture is scooped up by front-end loaders surprismgly, the Amur maple comes from and disposed of "out of the way" on the is- the harsh climate of the Amur river valley of lands, to the detriment of the vegetation China, which is bitter cold in winter and hot planted on them. and dry m summer. Our native eastern flow- ering dogwood (Comus flonda L.) grows poorly and is subject to drought stress and Ecological Requirements severe borer infestations in island plantings, The forested areas of the north temperate whereas the native species of hawthorns are zone contain a wide variety of tree and shrub excellent for such locations. The cornelian species. The greatest number occurs in cherry (Cornus mas L.), which grows out to areas where the old Tertiary forest was not the edge of the steppes of Russia, is another extirpated during the last Ice Age, particu- tree of choice. larly the eastern United States, Japan, and Island plantings of shade trees are par- parts of China. When cleared land is aban- ticularly exposed to wind damage. Al- doned in naturally forested areas, a gradual though the Bradford callery pear (Pyrus process of forest regeneration begins. The calleryana Decne.) is otherwise suitable for first trees are "pioneer" species that can islands, it is susceptible to breakage when it stand exposure to full sun and drymg winds. matures. It has been dropped by many state After these have colonized the open field and highway departments because of this but is matured, they are slowly replaced by so- still a favorite for sheltered locations in the called climax species, which are long-lived downtown areas of cities. The tough-wooded 166

bur oak (Quercus macrocarpa Michx.) can clones are much improved, however, and serve as an alternative to Bradford pear. This should rate high on the list of trees for tree comes from the Plams States, where difficult sites. The Norway maple will grow violent thunderstorms routinely occur each well in island plantings and in polluted con- summer. ditions in cities, where the sugar maple and red maple will not thrive. It is one of the few with attractive flowers, which are a Trees and Shrubs Recommended for Island species clear chartreuse color and abundantly borne. Planting The fall color is a fine yellow. The following is a list of trees and shrubs that have proved adaptable over a wide range L. 15- of soils and climates in the East and Mid- Acer pseudoplatanus Height 18 m~. Hardy to -30°F. Sycamore maple. west. For the subtropical climate of Florida and the desert conditions of the Southwest, Although it is not a particularly distin- of course, entirely different lists are needed. guished tree, the sycamore maple ranks high wherever salt spray or deicing salts are a After the hurricane in the summer Trees problem. of 1948, it was the only deciduous tree with Acer gmnala Maxim. Height 5-6 m. Hardy green leaves (no browning whatsoever) along to -50°F. Amur maple. the coasts of Rhode Island and Massachu- setts. Trees from are often mediocre, This small tree has the unique characteristic but the best clones of the variety purpureum of tolerance of extremes of heat, cold, and are vigorous and shapely, and the purple un- drought. It can be grown with several trunks dersurface of the leaves is particularly at- or pruned to a single stem. The Amur tractive. The tree tolerates soil, pave- maple’s beauty lies in its leaves, scarlet in dry ment glare, and alkaline or saline soils. fall and a glossy dark green in summer. A similar species, Acer tatancum, merely turns yellow in fall and is much less cold Celtis occidentalis L. Height 12-15 m. hardy. The Amur maple is very tolerant of Hardy to -50°F. Hackberry. salts and alkaline soil and can substitute The hackberry is one of the last trees to dis- well for the Japanese maple (A. palmatum)/ appear from the landscape as one journeys in the Midwest, where the latter is not west across the prairies. It also grows in the winter hardy. thin soil on basalt and granite hills m New England. It is not surprising therefore that it L. 15-18 m. Acer platanoides Height endures the stressful environments of island Hardy to -30°F. Norway maple. plantings. Plants from seedlings are variable, The common Norway maple has been much and many are subject to unsightly twig and maligned in recent years because trees of foliar diseases. Grafted clones are available, seedling origin vary greatly, and many are however, which are both shapely and disease distinctly inferior in growth habit, growth free. Clones and seedling trees are very rate, and quality of foliage. The best grafted tolerant of dry, alkaline soil and exposure. 177

The hackberry tree (Celtis occidentahs ~. Photo- graphs with this article from the Archives of the steppes of Russia. It is not as showy as the Arnold Arboretum. large-flowered species (Cornus flonda), but it becomes a haze of yellow in early April. Cornus mas L. 5-6 m. Hardy to Height The dark green leaves are thick and leathery -30°F. Cornelian cherry. and do not scorch in summer droughts. It is The toughest of the tree-sized dogwoods, the difficult to grow Cornus mas in tree form; it cornelian cherry grows wild on the bleak is best grown as a large clump. This tree is 188

ing spring. Unfortunately, no thornless clone of this species is available, but its thorns are much shorter and less dangerous than those of C. crus-galli.

Fraxinus pennsylvanica Marsh. Height 15- 18 m. Hardy to -40°F. Green ash. While the white ash (Fraxinus americana L.)[ is preferable for its superior autumn color, it is not as suitable for stressful environments as the green ash, which will tolerate drought, heat, cold, and saline and alkaline Cornelian cherry (Cornus mas).). soils with impunity. Seedling trees are vari- able, and many female trees set large crops of and defoliate very in the fall. As is free of the borers or diseases that plague early common to trees with a broad latitudinal Cornus flonda. range, green ash has a number of geograph- ical races. Trees grown from Florida seed are Crataegus crus-galh L. var. mermis. Height as hardy as orange trees in North Dakota, 6-8 m. Hardy to -30°F. Thornless cockspur while trees from North Dakota hawthorn. provenance grow as well as balsam fir would in Florida! The common cockspur hawthorn is one of Several fine male clones are available, all our toughest small trees, but because of its from the North Central States, where green long, needle-sharp thorns, it constitutes a ash is an important shade tree. ’Marshall’s danger in areas where pedestrian traffic is Seedless’ is unsmtable, however, because present. The thornless form has the favor- nurserymen have found that it has begun to able qualities of the species without the seed overabundantly. dangers: tolerance of drought and exposure, fine glossy foliage, and long-lasting red Gleditsla triacanthos L. var. inermis Willd. fruits. Height 15-18 m. Hardy to -30°F. Thornless honeylocust. Crataegus phaenopyrum (L.f.) Medic. Height The selection and introduction of a number 6-9 m. Hardy to -30°F. Washington haw- of thornless clones with crowns thorn. shapely have transformed the honeylocust from an One of the finest small-flowered trees for is- unattractive weed tree mto an important land planting. In the mini parks of tree. The thornless honeylocust is downtown New York City, it thrives under rapid growing, easy to transplant, and toler- the most adverse conditions. It is attractive, ant of very difficult urban environments. although not spectacular, in bloom. The Like green ash, it is among the trees that glossy foliage turns red in the fall, and the persist longest as one crosses the northern brilliant red berries hang on until the follow- prairie states with their harsh extremes of 199

climate and alkaline soil. Such tolerance for tree is young to prevent interference with adversity is an mdication of the honey- passing traffic. The thick, corky bark of ma- locust’s suitability for island planting. It is ture trees is an attractive feature. The particularly desirable for parking lots be- foliage, which is free of pests and diseases, cause its tiny leaflets blow away after drop- turns a clear yellow in the fall. Staminate ping and do not have to be removed. Though (male) trees are preferable for urban settings, cold hardy, it does not thrive in the very acid as pistillate (female) trees produce large soils of parts of Maine and Nova Scotia. crops of fruits.

Malus baccata (L.) Borkh. Height 9- Platanus x acerifolia (Ait.) Willd. Height 12 m. Hardy to -50°F. Siberian crab apple. 21-27 m. Hardy to -30°F. London plane tree. A native of one of the world’s harshest cli- mates, the Siberian crab apple is a first This vigorous hybrid is the city tree par ex- choice among flowering trees for island cellence, a standard agamst which others plantmgs. It survives drought and a wide must be judged. Tolerant of drought, poor range of soil conditions. The flowers are red soil, reflected heat, and atmospheric pollu- to pink in bud and pale pink to pure white on tion, it is easy to transplant and grows rap- opening. Bloom is heavy on alternate years. idly. The original clone, now often called the The tree is virtually immune to apple scab "Bloodgood strain" is resistant to anthrac- disease and mildew and resistant to fire nose leaf disease, which defoliates our native blight. In fact, in the Pennsylvania crab- sycamores during wet springs. The London apple trials, which have been conducted for plane tree has gone through several cycles of many years, the only clones to receive rec- popularity and disapproval. Many years ago a ommendations have been Malus baccata few nurserymen grew the trees from seed seedlings or hybrids derived primarily from that produced great variation m habit of baccata. A very desirable feature of this growth and disease resistance, and this may species is its disease-free foliage, a trait that be one cause for the disapproval. Another is shared by M. xatrosanguinea (F.L. Spath) may be the plane tree’s vulnerability to C. K. Schneid. and M. flombunda Siebold ex canker stam disease, a serious condition Van Houtte. Crab-apple trees chosen for is- spread by pruning tools or other mechanical land planting where pedestrian traffic is pres- means. The severity of the disease once led ent should be trees that bear tiny fruits or the city of Philadelphia to enact ordinances few fruits. that prohibited planting the tree. Still, where a large tree is needed for island planting, it is amurense 9- Phellodendron Rupr. Height a first choice. 12 m. Hardy to -40°F. Amur cork tree. Having originated in the fierce climatic ex- Pyrus calleryana Decne. Height 12- tremes of the Amur River valley, this small, 15 m. Hardy to -30°F. Callery pear. spreading tree easily endures poor, dry soil, reflected heat, and atmospheric pollution. The cultivation of the vigorous, thornless Its lower branches must be pruned when the ’Bradford’ pear by the U.S. Department of 20

Agriculture Plant Introduction Station at Sophora japonica L. Height 15-18 m. Beltsville, Maryland, transformed an un- Hardy to -30°F. Japanese pagoda tree. known, thorny scrub tree mto one of the This unusual summer-flowering tree has most popular street trees. This tree has ev- been in the nursery trade since the 19th cen- erything to recommend it: rapid growth, tury but only recently has become a popular beautiful pure white flowers, and richly col- street tree. It is one of the most variable of ored fall foliage. Like all pears, it grows well all species; a single seedlot can produce both in compacted, poorly oxygenated soil. Brittle dwarf weepers and tall, full-headed trees. wood is its only weakness, and mature trees Now improved clones with first-rate shade can literally collapse in a violent summer tree form are readily available. This species wind storm, as the parent tree did at tolerates soils the Beltsville. The Pennsylvania highway de- compacted (including " yard" soils of Washmgton, D.C.), high partment and others have removed it from pH, salt, drought, and polluted air. It is a their planting lists for that reason. However, conspicuous bloomer in August and retains for street or island plantings in more shel- its dark green leaves later in the fall than tered urban locations it is still an excellent other deciduous trees. Like it choice. Several cultivars that are more wind honeylocust will not grow in highly acidic soils, however. firm and/or more cold hardy than ’Bradford’ are now available in the nursery trade. Syringa reticulata (Blume) Hara. Height 6- 9 m. Hardy to -30°F. Japanese tree lilac.

Quercus macrocarpa Michx. Height 18- This tough, hardy small tree is covered with 24 m. Hardy to -50°F. Bur oak. huge pamcles of white flowers in June, after the season of most other Many species of oaks make excellent shade blooming flowering trees has passed. It withstands exposure and trees under ordinary street conditions, but alkaline soils and is not troubled by mildew few thrive m constricted island plantmgs, on the leaves or stem borers as are other especially where soil pH is high. Members of lilacs. The lower branches must be the black oak division of the family (pin, red, pruned when young so that they will not interfere scarlet, willow, and black oaks) turn yellow with pedestrian traffic. Several clones are from chlorosis under these circumstances now available, including one from Canada. and gradually die out. The bur oak is unique These have been selected for their superior in that it grows well in alkaline soils, stands and blossoms. drought, heat, and cold and is tolerant of foliage, growth habit, larger deicing salts. It is not so easy to transplant as Tilia cordata Mill. 15-20 m. the pin oak but is comparable in this regard Height Hardy to -30°F. Small-leaved European linden. to red and scarlet oaks. It grows slowly but becomes a tough, long-lived tree. Its native Lindens in general grow well under city con- range extends farther west than that of any ditions, and the best clones of this species of the other eastern oaks, which means that are especially reliable. Like those of the it is naturally adapted to ecological condi- pagoda tree (Sophora japomca populations tions similar to those of island plantings. of small-leaved lindens grown from seed are 21

extremely variable. Growth may be either rapid or slow; wood is sometimes weak; and leaves may be small and leathery or large and easily scorched. Grafted trees do not ex- hibit graft mcompatibility and reproduce exactly the very best forms. Easy to trans- plant, fairly rapid m growth, and tolerant of many soils and climatic conditions, they are excellent subjects for urban islands. The flowers are not conspicuous, but their rich fragrance is a great rarity among shade trees.

Tiha x euchlora C. Koch ’Redmond’. Height 12-15 m. Hardy to -30°F. ’Redmond’ lin- Flowers of the tree lilac re- Japanese (Synnga den. ticulata).~. Much controversy exists as to whether this tree is a Crimean or an American linden cul- The small-leaved European linden (Tiha cordata)./. tivar. It has the large leaves and resistance to spider-mite attacks characteristic of Amer- ican lindens. A compact, upright tree that is native to Nebraska, it is mured to climatic extremes of heat, cold, and drought and thrives m urban locations.

Ulmus x hollandica Mill. hybrids. Height 15-18 m. Hardy to -30°F. Dutch elm. The Dutch elm disease, which was first identified in Holland, has destroyed a major portion of the splendid elm populations of Europe and during this cen- tury. In response to the crisis, the Dutch government selected and bred elms to pro- duce forms that would be immune to the disease. Seven clones were distributed, some of which have demonstrated remarkable re- sistance to even the most virulent strains of the fungus. These have the upright, rectan- gular crowns of European elms rather than the wine-glass shape of American elms. Al- though vulnerable to elm-leaf beetle, they are exceptionally well adapted to urban 22

street conditions and grow well in narrow these sites. They must be tolerant of poor planting pits and poorly oxygenated soil. soil, drought, and exposure to wind and heat. Salt spray is just as damaging to shrubs as to trees m island plantings, and it is not sur- Zelkova serrata (Thunb.) Mak. Height 15- prising that several of the species listed 18 m. Hardy to -20°F. Japanese zelkova. below are also first choices for seashore planting. In addition, like are Not many decades ago this species was shrubs, trees, rarely encountered outside arboreta and bo- vulnerable to the problem of vandalism. The New York City Public tanical gardens. Seedling trees are very vari- Housing Authority has found that it is best to avoid shrubs with able, and most have irregular, zig-zag habits of growth and small yellowish foliage. The conspicuous flowers except for extremely vigorous growers such as All of the original introductions came from the forsythia. shrubs listed below are on the list warmer regions of Japan and were not too approved for the and have withstood the cold hardy. It was not until the Dutch elm authority severest tests of in disease destroyed the American elm and the time very unfavorable search began for replacement species, that inner-city conditions. They are relatively free from diseases and insect and can zelkova began to receive serious attention. pests Hardier clones with excellent shade-tree truly be termed low-maintenance shrubs. Shrubs that grow to be too tall for their lo- shapes are now available and are being cation can be cut down to the widely used on city . Tolerant of pol- safely ground lution, drought, and heat, they have shown and will resprout and grow more densely than ever. On level sites a remarkable vigor in downtown locations in well-sharpened brush mower can be used at a Washington, D.C., and Baltimore, Maryland. great savings in labor costs. Cutting back is best done in They are not as cold hardy as most impor- November or December so that the cut sur- tant shade trees but otherwise are excellent faces can out and seal themselves before choices for island planting. Any tree with dry the to run m the cut- such a wide native distribution as zelkova sap begins spring. Also, off at this time will result in the most must have hardy races m the colder parts of ting its range, and a serious attempt to find them vigorous regrowth. would increase the uses of this excellent tree. Although artifical innoculations of Zelkova serrata with the Dutch elm fungus have demonstrated that this species is vul- Acanthopanax sieboldianus Mak. Height nerable to the disease, this factor can be ig- 2-3 m. Hardy to -30°F. Five-leaf aralia. nored because the insect vectors of the dis- This dense, many-stemmed shrub is ease do not feed on this tree. espe- cially tolerant of poor, dry soil and atmo- spheric pollution. It is thorny and makes an excellent barrier Shrubs planting. Other than its abundant disease-free foliage, it has no spe- Shrubs for urban islands should share the cial beauty but is most useful for its vigor same characteristics as trees chosen for under adverse conditions. 23

Berberis thunbergii DC. Height 2 m. but, being thornless, it should not be planted Hardy to -20°F. Japanese barberry. where it can be trampled by pedestrians. Several forms that are lower and more Japanese barberry plants were once sold by spreading are grown in Japan, but unfortu- the millions for low-growing , but nately these are not available in this coun- their use has declined as formal clipped try. hedges have lost popularity m home gardens. It is still useful as a barrier and tall ground cover, however, and will grow well in condi- Elaeagnus umbellata Thunb. Height tions of poor soil and neglect. The numer- 3-4 m. Hardy to -40°F. Autumn olive. ous, small thorns are needle sharp, a real de- The foliage of this species is not so showy as terrent to without trespassers being danger- the pale silvery leaves of the Russian olive ous. The brilliant shades of scarlet in foliage (Elaeagnus angustifoha~. Yet is has the ad- the fall and the persistent red berries are very vantage of being better adapted to the East- attractive. The redleaf form is colorful ern States and other areas where summer throughout the growing season. humidity is normal. The extensive highway plantmgs of Russian olive m the East in the 1950s all have succumbed to Chaenomeles lagenana (Loisel.) Koidz. gradually twig blight, while the disease-free autumn olive Height 1-2 m. Hardy to -30°F. Flowering has become naturalized in the quince. extensively same areas. Autumn olive is a superb tall One of the most colorful early-flowering shrub for roadway or seashore planting, shrubs, the flowering quince resists van- withstanding salt, poor soil, and drought dalism because of its numerous prickly without setback. The silvery green foliage thorns. It is a popular substitute for the and pretty bronze-to-red fruits are decidedly Kurume azaleas m cold areas where the lat- ornamental. The U.S. Soil Conservation ter are not winter hardy. There are numer- Service has introduced a strain grown from ous named clones with flowers ranging in seed called ’Cardinal’ with fruits that are a color from pure white through various bnghter red. shades of pink and orange to deep crimson red. They vary m height and density, and the Forsythia x intermedia Zab. Height 2 m. low, bushy forms are excellent for ground to -20°F. border cover. Hardy Showy forsythia. Wherever it is wmter hardy, this is one of the best shrubs for screening purposes. It is Deutzia Siebold & Zucc. gracilis Height vigorous, pest free, tolerant of city condi- I m. to -30°F. Slender deutzia. Hardy tions, and unaffected by deicing salts. Van- This low, twiggy shrub has greatly in- dals do break off branches m the blooming creased in popularity m recent years for the season (April), but the plant quickly recovers purpose of mass plantmgs. It is covered with from the injury. pure white flowers m May and has abundant Three excellent new clones of the much pest-free foliage. It is also useful as a hardier Forsythia ovata have been bred for 24

the northern Plains States and Canada, shrub, spreading gradually by underground where border forsythias will survive. runners.

Ligustrum obtusifolium var. regelianum Potentilla fruticosa L. Height 1 m. Hardy (Koehne) Rehd. Height 2 m. Hardy to -40°F. to -50°F. Bush cinquefoil. Regel privet. This hardy, drought-resistant shrub is This is the only hardy privet that is low smtable for mass planting in full sun but growing, dense, and spreading, and excep- does not thrive in shade. It is not spectacular tionally useful for mass planting. One of the m bloom, but the pretty yellow flowers are toughest shrubs for city use, it is a mainstay borne over a long period during the summer. for adverse sites. Almost 100 years of exten- It is especially useful where summers are sive planting in New York City and else- dry, with low humidity. Many cultivars are where have shown that it is one of the most available, varying in flower color, habit of reliable shrubs for city landscaping. growth, and tolerance for adverse condi- tions. ’Katherine Dykes’ is among the best for use. Lomcera fragrantissima Lindl. & Paxt. ground-cover Height 2 m. Hardy to -10°F. Winter honey- suckle. Prunus maritima Marsh. 1-2 m. Hardy to -40°F. Beach plum. This handsome semievergreen shrub is This was once a rarely grown native shrub often listed as hardy to -20°F, but it is bet- chosen by landscape ar- ter grown at minimum winter temperatures knowledgeable chitects for mass m seashore of -10°F and above. It has leathery foliage plantings gar- dens. It is now extensively used, not only for and deliciously fragrant flowers, which open the traditional seaside but also for in March in the south and in April further uses, because it is so tolerant of north. It withstands poor soil and polluted roadway planting, salt spray and poor, sterile soil. The white air and is free of pests and diseases. Young flowers are attractive m the spring, and the plants are sparsely branched but fill out with fall is more colorful than that of age to form an impenetrable screen. foliage many other plums. The dense branching habit renders it useful for barrier Myrica pensylvanica Loisel. Height 2 m. planting. Hardy to -40°F. Bayberry. Rosa rugosa Thunb. Height 1 m. Hardy to One of the three most shrubs appropriate -50°F. Rugosa rose. for the seashore, bayberry has proved to be equally indispensable for roadways. It grows Generally regarded as the most beautiful wild in the poorest, most sterile soils and of all the wild rose species, this splendid withstands salt spray, heat, drought, and pol- shrub is unsurpassed for mass planting. It is luted air. It is semievergreen in the southern a seashore plant in its native Japan and has part of its range, and the foliage is pleasantly become widely naturalized in this country aromatic. The gray-white berries of female on the East Coast. The red, pink, or white plants last far into the winter. This is a dense flowers are deliciously fragrant, and the 25

Arrowwood (Viburnum dentatum) / m flower.

handsome disease-free foliage turns orange status, these plants are an exceptional group and red in the fall. It thrives along the of shrubs for mass plantings in adverse loca- seashore and in adverse urban locations. tions. They are covered with fragrant pink Like other shrub roses, it benefits from being flowers in June, and their glossy foliage turns periodically pruned to ground level and scarlet in the fall. The red new stems and grows best in full sun. Rugosa rose has the abundant red fruits are colorful throughout advantage of blooming throughout the the wmter. Easily transplanted, they with- summer, unlike most other wild roses. stand drought, salt spray, and exposure and are free from pests and foliar diseases. Rosa mrgimana Mill. Height 1 m. Hardy to -40°F. Virginia rose. Symphoricarpos xchenaultii Rehd.’Han- cock’. Height 45-60 cm. Hardy to -20°F. This the shining rose /Rosa nitida~, species, ’Hancock’ coralberry. and several other native species comprise a confusing group of very similar wild roses of This low, rapidly spreadmg shrub from doubtful identity. Whatever their taxonomic Canada is an excellent ground cover in full 26

or partial sun. It has tiny, neat foliage and figure 1). Plantings often fail when the soil is spreading branches that root wherever they graded to an even crown so that water runs touch the ground, forming a dense mat. off mstead of being absorbed. As noted ear- Coralberry grows well m poor soil and is free lier, the surface area for rainwater infiltra- of pests and diseases. tion is very limited in island plantings, and because islands are surrounded by pave- Viburnum dentatum L. Height 3-4 m. ment, which carries off precipitation, the Hardy to -50°F. Arrowwood. subsoil beneath is usually deficient in mois- ture. Thus, little capillary replenishment to This splendid shrub is one of another cluster the root zone can occur. of species whose identity is doubtful. Al- Because islands are small and their soil is though it inhabits wet, lowland areas in the often too much or humus is fre- wild, it is also drought tolerant and with- poor, peat quently added to the beds. Many old backfill stands salt spray and exposure. The foliage specifications called for up to a third or a half and stems are immune to the stem cankers of the mix to be well-rotted manure or other and leaf spots that disfigure other hardy forms of humus. Trees initially grow vigor- viburnums. The berries are an mconspicu- ously in such high-humus soils, but when ous blue-black color, but the yellow and red the surrounding soil is clay, they to fall color of the foliage is first rate. begin slow down and stagnate in a couple of grow- mg seasons. Orgamc matter of any kind is Viburnum prunifolium L. Height 4-5 m. soil bacteria and Hardy to -40°F. Black haw. gradually decomposed by eventually disappears into the atmosphere One of the tallest native viburnums, the as carbon dioxide. As the volume of humus black haw makes an excellent screening m the backfill disappears, the tree settles plant and can also be sheared to create a deeper in the soil and roots become situated formal hedge. This is an upland species, in- too deeply for proper growth. Arborists and ured to poor soil and drought. In autumn the landscape architects are now re-exammmg smooth oval leaves mitially turn pmk, then the old specifications for soil amendment. and red, finally purple. The berries also Unless the soil on the site is entirely unsuit- change from green to pmk and finally blue- able - a mixture of brickbats and rubble for black in the fall. example - they recommend adding fer- tilizer and enriching the existing soil with a minimum of not more than 10 Island Tree Planting humus, per- cent. Such minimal treatment avoids the Island beds for tree plantmg should be raised interface problems that can occur when the well above the level of the surrounding backfill mix is very different in texture from pavement. The runoff from the impermeable the soil in which the planting pits were ex- pavement can so concentrate rain and snow cavated. Since trees for island plantings have melt in a sunken island that death from root to be large enough in caliper to withstand rot can occur. Although raised above grade vandalism, they are usually balled and bur- level, the surface of the island also should be lapped rather than container-grown. These somewhat dished to retain rainwater (see transplant with little difficulty and do not 27

Figure 1. Dished island surface crowned surface

Figure 2. Planted high Planted too deep

Figure 3. Improved method Traditional method Edges of basin placed over edges of ball 28

need high-humus backfills. If the existing enough from the perimeter of the island so soil is a heavy clay and requires lightemng that the bumpers of cars will not debark the for proper air penetration, coarse sand, cal- trunks or flatten the stems. The large auto- cined clay particles, or similar nonorganic mobiles of the 1960s are no longer common, materials should be used. but even small cars have substantial over- Whenever trees are planted in newly hangs. In far too many island plantings, trees worked or loosened soil, they should be set become will established initially but even- "high" in relation to the final grade level (see tually succumb to repeated debarlang by figure 2). The ideal system is to place the ball careless drivers. on an unbroken column or pedestal of undis- turbed soil so that it cannot settle, though William Flemer III is the propnetor of Pnnceton Nurs- enes, Pnnceton, New Jersey such extra care is impractical in all but a few planting situations. An alternative solution is high planting, 5 cm above grade for the top of a 60 cm ball, 8 cm for a 90 cm ball. It is far better to err on the side of too shallow rather than too deep planting. A famous example was the red oak leading to the - gers University in New Jersey. The land on the site was a very poor red-clay soil, so generous amounts of rotted manure were incorporated in the backfill. The trees all lived and grew well for the first two growing seasons, only to stagnate later on. Eventu- ally all the trees were dug up again and reset with the tops of the balls above grade, and thereafter they grew beautifully. High plant- ing is the best way to avoid these difficulties. Most plantmg specifications for shade trees recommend forming a shallow berm around the edge of the planting pit to facili- tate watering. Experience in , where water is scarce and expensive, has shown that the basin is much more effective if the edges are placed over the edge of the ball (see figure 3). Particularly m sandy loca- tions, this assures that the ball itself is well watered during irrigation and that the mois- ture does not slip down the side of the pit. One detail that is often overlooked in is- land planting, especially in parking lots, is to ensure that trees and shrubs are planted far