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L E SSO N S F R O M
N O R T H E R N E U R O P E
expanding your plant palette Mary Forrest, Professor at UCD School of Agriculture and Food
Science, provides a fascinating insight into the trees and shrubs of Denmark, many of which could be effectively used in the Irish landscape
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enmark and Sweden are seldom visited for their gardens, parks and open spaces, at least by Irish horticulturists. A tour with the International Dendrology Society to Denmark and southern Sweden in June 2017 was an eye opener to the wealth of trees and shrubs cultivated. While the landscape elements in suburban gardens, parks and open spaces are similar to this country, many of the trees, shrubs, climbers and hedges cultivated are unfamiliar or cultivated differently. They provide new ideas for the design and management of planting schemes in Ireland.
SOME TREES WORTH PLANTING Zelcova serrata, a relative of Ulmus (elm), is a well branched wide spreading, smooth barked tree to 20m with finely pointed ovate foliage and good autumn colour. More elegant that Carpinus betulus ‘Fastigiata’ (hornbeam), it is suitable for a space where Fagus (beech) would become too large a tree. Cercidiphyllum japonicum f. pendulum is a weeping graceful tree, less angular than Fraxinus excelsior ‘Pendula’ (weeping ash). The leaves are opposite and round. Each spring the emerging amber coloured young foliage permeates the air with a sweet scent, this colourful display is repeated in the autumn. As in Ireland, Japanese maples (Acer palmatum) were popular in suburban gardens and in tree collections. Their cultivation as a hedge is unusual but effective since when not in leaf, many branched stems continue to act as a screen (Fig 1). Many other small to medium sized maple species were cultivated; Acer carpinifolium, as the name indicates has hornbeam-like (Carpinus) foliage, produces plenty of seed; A.trautvetteri is a beautiful fast growing tree with seeds which become an attractive red colour, and A. sempervirens is a neat tree with the typical three lobed leaves of maple foliage, stiff to the touch and distinctly parallel sided seed. Although Liquidambar styraciflua (liquidambar) is growing well as a street tree in Dublin, providing rich autumn colour, it flowers in Copenhagen. Clusters of female flowers, green ones from this year and reddish from last year, hung beneath the maple-like foliage.
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While birch is native in Nordic countries species from Manchuria, Japan and China trees were frequent in tree collections in Denmark and Sweden. Betula costata is a tall growing tree with ‘very’ peeling bark on main trunk, less so on well coloured branches. Betula ermanii has pale coffee coloured smooth bark on branches and upper part of the trunk. Betula davurica, again with a shaggy peeling bark, was planted in a few collections. Though in leaf the branch coloured and peeling papery nature of the bark was obvious, these trees growing as specimens or in groups must be spectacular in winter. Ptelea trifoliata (hop tree) a deciduous wide spreading tree was commonly planted in gardens and tree collections. In late June to July it looks attractive from a distance with shiny trifoliate leaves and a ‘haze’ of white flowers. On closer inspection they were clusters of dainty star-like flowers. Gleditsea triacanthos ‘Rubylace’ is a small specimen tree. It was well placed by a flight of steps in a suburban garden where brown tinted bark and bronze coloured pinnate foliage could be admired from above and below. Flowers were the noticeable features of two other leguminous plants. Colutea arborescens (bladder senna) is a 1m tall deciduous shrub summer flowering shrub with pinnate leaves. The bright yellow pea-like flowers each with delicate orange markings are succeeded by pea-like seed pods which swell to what is commonly called a bladder. Indigofera amblyantha is an elegant tall shrub to 2m, with small pinnate leaves. Pale pink or mauve flowers are borne over a long flowering from June to October, a time when few shrubs are in flower. While both genera are grown in Irish plant collections they deserve wider use as summer flowering shrubs in dry sunny situations.
SHRUBS AND CLIMBERS FOR LANDSCAPE SCHEMES Viburnum tinus and V. davidii are stalwarts of landscape schemes in Ireland but other species are worth planting. Viburnum ‘Pragense’ is a medium sized shrub, a hybrid of V. rhytidophyllum and V.utile. The foliage is evergreen, like a smaller version of V. rhytidophyllum but with glossy rather
/ www.horticultureconnected.ie / Spring 2018
