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This time of year is sometimes considered perilous in the garden. Obviously, there’s the potential for ice and snow, and the danger those pose to pedestrians and to brittle-branched, broadleaved evergreens like Magnolia grandiflora, but the greater shame, it seems to me, is the attitude that the garden is not worth visiting in the winter. And considering that we might suffer a significant freeze and miss out on the amazing array of winter flowers—note that a number of camellias, winter viburnums, mahonias and confused rhododendrons are in bloom as I write—the winter chill brings out another dimension in the garden we should consider. And that is the importance of broadleaved evergreens to the garden structure. Plenty of ink has been spilt here on the subject of rhododendrons, and while this is a practically inexhaustible subject to me, and worthy not least because of their diversity, size and sheer numbers in the Garden, it’s always worth discovering and exploring other groups of broadleaved evergreens.
Osmanthus—the sweet-olives—are easily recognized by their sizeable, oppositely-arranged, leathery, usually toothed, evergreen leaves. One of the most attractive of this tribe is Osmanthus serrulatus (fine-toothed sweet-olive), which hails from the mountains of southwestern China. We have a single plant in the David C. Lam Asian Garden, near the corner of Rock and Decaisne Trails. It is a large shrub, now becoming almost tree-like, with long-pointed, uncommonly dark green, lustrous leaves. In April, plants produce pompom-like clusters of small, fragrant white flowers between each set of the previous year’s leaves. The flowers of osmanthus are often small, but frequently powerfully fragrant. In fact, the genus name means fragrant flowers. If we had another in the vicinity (i.e., a different seedling of the same species), we’d undoubtedly see masses of blue, lozenge-shaped fruits in autumn. Alas, Osmanthus species are self-incompatible, and require cross pollination to set fruit. A similar-looking sweet-olive, but with fewer discernable marginal teeth, is Osmanthus yunnanensis (Yunnan sweet-olive). The vigour of this plant is substantial. Our plant, visible below the boardwalk east of the Campbell Building, is kept to a reasonable 2.5 m by 2.5 m by annual pruning. It would make a sturdy tree, otherwise.
A few metres away on Cox Trail (and also where Wharton Trail meets Kingdon Ward Way, and another above Lower Asian Way west of Meyer Meadow) is the smaller-leaved, but tree-like, Osmanthus suavis, the sweet sweet-olive (Latin: suavis= sweet), with leaves that are like miniature versions of O. serrulatus. This one has my vote as the most attractive of the sweet-olives when flowering – see Daniel Mosquin’s exceptional image in our Flickr album. The largest of our sweet-olives is Osmanthus decorus (on Beer Trail just below Campbell Glade). While its leaves are much the same size as those of O. serrulatus and O. yunnanensis, the plant is a monstrous, sprawling shrub that can grow to more than 10 m tall and even wider in diameter. Its primary claim to fame (other than being generally unmanageable) is as a parent of the excellent landscape shrub known as Burkwood sweet-olive. The other parent, Osmanthus delavayi (Delavay sweet-olive) has leaves about the size of an average fingernail. There is an unruly specimen on Delavay Trail just west of Wharton Glade. Both species are known for the heady fragrance of their flowers, and the hybrid is noted for this, as well as for a leaf size and stature intermediate between the parents.
A close relative of Osmanthus is the Mediterranean genus Phillyrea. High in the Asian section of the E.H. Lohbrunner Alpine Garden is Phillyrea latifolia (broad-leaved phillyrea). Visitors would be forgiven for assuming that this plant is Osmanthus x burkwoodii, as the two are remarkably similar, both in shape and leaf size, although the leaves of the Phillyrea are more papery. The two genera differ primarily in their fruits, which are dry and papery in Phillyrea and juicy in Osmanthus. Finally, the hybrid tea-olive, Osmanthus x fortunei, which is a cross between the tender O. fragrans (tea-olive) and the spiny-margined O. heterophyllus (holly-leaved sweet-olive) is planted in the Winter Garden as well as in the Asian Garden above Lower Asian Way, west of Meyer Meadow. The flowers are small, but intensely fragrant, smelling of sugared apricots, and nearly obscured by the softly spine-margined leaves. As long as winter temperatures don’t stay below the freezing mark for long, the hybridtea olive will generally have open flowers from Halloween through January. This plant was introduced to the Netherlands from Japan in 1856 by the German physician, naturalist and explorer Philipp Franz Balthasar von Siebold, thence to England in 1862 by the Scottish botanist and plant hunter, Robert Fortune, for whom the shrub is named.
Submitted by: Douglas Justice, Associate Director, Horticulture and Collections