Looking after willows in winter

The cruel winter has been kind to Oxford’s trees; it’s years since our willows looked so colourful. The water meadows and riverside walks are galleries of gold and scarlet. Their twigs always oblige with these hues as a prelude to spring, but never more brilliantly than after a long-awaited thaw. Cold assists in their colour conversion, turning stored-up sugars into pigments, which are released in a burst of vernal anticipation.

Taking their cue from the landscape, owners of several Oxfordshire estates have embraced local willows, and the old techniques for maintaining them. Not only do these trees stabilise sodden ground and mitigate floods, they’re also better-looking than anything from further afield-consider the flickering silver dance of the white willow (Salix alba) when in leaf, or the exuberance of the common osier (Salix viminalis) when, as now, it is a haze of gleaming rods. I’ve seen both introduced to marshy tracts, producing either casual scenes reminiscent of Corot or more radical, Modernist designs. Although one of the oldest and most familiar features of country life hereabouts, a channel fringed with willows and reeds can be used to construct water-framed grids of hedges and avenues, giant parterres and even spiral labyrinths.

Meanwhile, Oxford University’s gardens favour the domesticated equivalents of these wild willows. Lakes and pools are ringed with ember-red Salix alba Britzensis and S. alba var. vitellina, which looks like extruded sunshine. Away from the water’s edge, Salix daphnoides sports stems in violet-black, and its cultivar Aglaia is a thicket of polished purple-red. Then there’s Salix exigua, the coyote willow, a native of sandbanks in the wide rivers of the Wild West and one of the finest shrubs to become available in recent years. With twigs in amber and amaranth and slender silver leaves, it’s as valuable in a high-summer border (among roses, for example) as it is in a late-winter shrubbery.

With shoots in red, plum and yellow respectively, the dogwoods Cornus alba Sibirica and Kesselringii and C. sericea Flaviramea repeat the willow effect on a smaller scale. In a month or so, these and the Salix cultivars will be stooled-pruned hard to within a few inches of the ground. At the same time, the larger willows used in wider landscapes are coppiced, with last season’s branches cut off just above a low and permanent stump.

Harsh though it seems, this is the best way to ensure next winter’s crop of painted wands. It also keeps these otherwise unruly trees and shrubs within bounds. On drier ground, two equally vivid specimens require only light pruning in mid to late spring. These are Cornus sanguinea Mid-winter Fire, a smaller, shrubbier, coral-and-flame dogwood, and Acer palmatum Sango-kaku, a Japanese maple whose leafless frame runs lacquer red.

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In gardens, these shrubs are by no means confined to the water margin-they will flourish anywhere that’s reasonably damp. In non-aquatic sites, they do, however, cry out for underplanting, being brilliant but bare. There are some obvious candidates-snowdrops, scillas, winter aconites and Arum italicum Marmoratum; grassy evergreens such as the variegated sedge Carex Ice Dance and the golden woodrush Luzula sylvatica Aurea; Bergenia cultivars with cold-burnished leaves such as Overture and Sunningdale, and all hellebores without exception.

In addition to these, Oxford’s shrubberies are carpeted with linctus-scented winter heliotrope (Petasites fragrans), and Pachyphragma macrophyllum, an underused groundcover with dark green foliage and sprigs of snowy flowers. Loveliest of all is Lathyrus vernus, a free-standing perennial pea whose finely cut foliage arises the moment winter retreats. Its flowers shift with age through rose, purple and kingfisher blue, until finally they fade, leaving you to declare with mixed regret and relief that spring has truly arrived and that it’s time to start stooling the willows and dogwoods.