Rowans to suit small gardens

Press, 2 June 1989, Page 11

Rowans to suit small gardens

Oardener’s H DIARY

Derrick Rooney

If you are looking for an attractive small tree to plant this winter — and you should be, if you don’t have sufficient trees already, because all gardens benefit from having at least one tree — and if you want one that will be pleasant to look at for different reasons in different seasons, you might well consider selecting one of the numerous forms of rowan.

The rowans comprise the major section of the genus Sorbus, a large, cosmopolitan genus of trees which includes many species with fine flowers, or foliage, or fruit, or all three.

All have a common character — narrow, pinnate leaves with more-or-less numerous small segments — that separates them from the other major group of sorbus species, the whitebeams. The latter have simple leaves, lobed or toothed sometimes, but not divided into segments. The whitebeam itself, Sorbus aria, is fairly rare in New Zealand. A native of Britain and Europe, it is a slow-growing, round-headed tree with oval leaves, conspicuously white underneath. The flowers are inconspicuous, but the fruits are attractive when they ripen crimson in autumn, about the same time as the leaves turn russet and gold. In Britain, at least 10 cultivars, including two with golden or yellowgreen foliage, are grown, and there is a second species, Sorbus anglica, a very rare native of western Britain, which is similar but smaller, and thus more useful in the garden. S. torminalis, the serviceberry, is related but has maplelike leaves.

The common rowan is S. aucuparia, also known as “mountain ash.” A familiar tree with narrow leaves divided into 11 or more small, toothed leaflets, it is naturalised in parts of New Zealand. The white flowers are hawthornscented, and appear in early summer, in flattish clusters. The bright, orangered fruit ripen in autumn. Numerous cultivars or hybrids, selected mainly for their larger or differently coloured fruit, are available in New Zealand now. Among them are “Xanthocarpa” (also known as “Fructuluteo” and "Fifeana”), which is very erect-growing when young (the crown rounds out later) and has amber-yellow fruit; it won an Award of Merit from the Royal Horticultural Society away back in 1895. “Kirsten Pink,” my favourite, is a Dutch-raised hybrid with pink fruit; it grows quickly, fruits precociously and appears to be immune to pear-slug, which can debilitate some of the rowans. “Fastigiata,” which I have ordered to fill a vacant space this winter, is slow growing, with very erect branches, making a narrow column.

The Asiatic relatives of the rowan include some lovely small trees, almost any of which, where space is limited,

might take precedence over the European forms. “Joseph Rock,” introduced to cultivation from seed sent home by the famous American botanist, is one of the finest. Small, slow-growing and almost shrubby, it bears large, yellow fruit. Of Chinese origin, it may be an undescribed species or a natural hybrid. S. prattii, also slow growing, has large, pearly white fruit but has been reluctant to produce them in my garden. S. cashmiriana has large white fruit and — maybe uniquely among the rowans — pink flowers. S. hupehensis, much planted in Central Otago, has elegant, glaucous leaves, and fruits that ripen pinkish white and hang on long after the leaves have turned crimson and fallen.

S. vilmorinii is a small, shrubby tree with very small, dainty leaflets and fruits that reverse the natural order: they begin in red, and turn white as they ripen. S. esserteauana “Fiava” has large, flat clusters of lemon yellow fruit. The leaves are dull green above but underneath are covered with greyish down; they look good on breezy days. S. discolour (of gardens) is also known as “Embley” and has exceptionally rich autumn foliage colour — the leaves turn glowing red and hang on the branches for several weeks.

Worth seeking out is S. ursina, also known as Sorbus sp. “Lowndes” after Colonel Donald Lowndes, who introduced it from the Himalaya to cultivation in Britain.

A small tree with erect branches, grey bark, and leaves divided into as many as 21 leaflets, each with conspicuous veins, it has marble-sized white fruit, often tinged red. Sometimes, as in S. vilmorinii, the fruits turn red when semi-ripe but fade to white later. This is a most handsome small tree which has only recently become available in New Zealand

Several hybrids, of English origin, between the European and Asiatic rowans are now available in New Zealand. They have names like “Apricot Lady,” “Sunshine,” and “Winter Cheer.” I chose "Sunshine” because the shortish internodes on its stems suggested that it might be slow growing, and because the label said it had bright yellow fruit; I wanted a tree with yellow fruit.

If I had more space I would be tempted also by S.X. Kewensis, a hybrid raised at the famous London garden in the 19305. It is a cross between the common European rowan and a Chinese species with a difficult name: S. pohuashenensis. A mediumsized tree blessed with hybrid vigour, it has big clusters pf orange-red fruit that weigh down the branches in autumn. In a new garden I would certainly plant it in preference to the common rowan.