Q: My little courtyard looks bare under its high oak canopy. Is there a small tree that will both survive in the shade and be interesting to look at — even in winter? — Charlotte Maynard, East Hampton, N.Y.
A: If one must plant beneath trees, oaks are among the most gracious of hosts, thanks to their benevolently deep roots and nonmatting leaf litter, which gives understory neighbors room to breathe. The acidity of most oak leaves is not the problem it’s commonly believed to be; in fact, shredded oak foliage makes some of the finest leaf mold or mulch. What really limits your selection of small trees is the filtered light coming through the canopy overhead. Fortunately, there are several likely candidates.
That old standby Japanese maple is colorful, graceful, and just the right scale. One caution, though: Maples with burgundy foliage lose much of their vibrancy in shade. Instead, try the golden-leaved full-moon maple, Acer palmatum ‘Aureum,’ which glows anywhere. Shadblow, Amelanchier arborea, is an appealing understory tree whose fall foliage spectrum ranges from straw yellow to scarlet. The open-growth habit of its branches responds to artistic pruning, a boon for gardeners who value elegant structure. It’s an easy step from admiring the silhouette of trunk or branch to appreciating the beauties of bark. Clethra barbinervis has perhaps the finest bark of all. As its outer layers flake off with age, the trunk becomes mottled with silver and orange. Cornus officinalis, which also peels handsomely, runs a close second in the bark department. If you crave flowers during the dormant season, seek out one of the hybrid witch hazels, named cultivars of Hamamelis x intermedia. The red, copper, or yellow blossoms they produce in late winter give off a heady aroma. If you can postpone floral satisfaction until early spring, opt for Eastern redbud, Cercis canadensis. My own choice for a courtyard tree is Japanese silverbell, Styrax japonicum. Its horizontal branch pattern is pretty year round, but you will have to wait till June or July to sit under its dangling clusters of fragrant white or pink blooms.