Dry and shady gardens: a double whammy
Most gardeners would agree that gardening in full shade presents certain difficulties, and I dare say that all would agree that gardening in dry, compacted soil is an even greater challenge; but combine the two, and you have a serious gardening hardship.
Dry shade is almost always the result of mature trees with roots that run close to the soil surface, taking up water before it has a chance to reach other plants. While non-native maples tend to lead the pack in this respect, dry shade is a fact of life at the base of most large trees. Worse still, your natural inclination to add more soil and raise the grade won’t work because vigorous feeder roots quickly invade and out-compete new understory transplants. Also, raising the grade above tree roots more than four inches (10 cm) may compromise the tree.
In my own garden, I have to contend with several areas of hardcore, dry shade. To deal with it, every autumn I loosen the existing topsoil with a garden fork, and add a six-inch (15-cm) layer of shredded leaves to improve the soil’s tilth and texture. I then top the layer of shredded leaves with a one-inch (2.5-cm) layer of compost or composted manure for additional nutrients.
Some shade lovers, such as Siberian bugloss and bigroot geranium, are naturally hard-wired to cope with dry conditions, while others (‘Ice Dance’ sedge, for instance) would, given their druthers, prefer much more moisture — thereby enabling them to launch a large-scale botanical incursion; but within the strictures of “dry shade,” they behave like perfect gents.
When installing perennials in these demanding conditions, add plenty of composted manure to the planting holes. It’s easier to plant in individual holes, rather than trying to dig an entire bed at once, and smaller plants get off to a stronger start than larger ones because they adapt to coexisting with tree roots more easily. Digging into soil filled with tree roots means it’s inevitable a few of the roots will be cut, but avoid cutting those more than two inches (5 cm) in diameter — doing so may damage the tree. Water at least once a week while plants become established. (Small plants need less water to get established, too.) During periods of prolonged drought, even mature clumps may need supplementary irrigation.
Most perennials that are able to tolerate dry shade bloom from early spring to midsummer, so mixing and mingling foliage types will ensure visual interest is sustained even when plants aren’t in flower.
8 great perennials for dry and shady gardens
Wild ginger (Asarum canadense)
This native groundcover bears downy green leaves that conceal distinctive burgundy to brown spring flowers borne at ground level. Taking several years to establish, mature patches can be divided in early spring or late autumn. Deer resistant and hardy to Zone 3, wild ginger grows four inches (10 cm) tall with an indefinite spread.
‘Looking Glass’ Siberian bugloss (Brunnera macrophylla ‘Looking Glass’)
This is a naturally occurring sport of B. m. ‘Jack Frost’, and a sizeable clump of ‘Looking Glass’ brunnera can lighten up the darkest corner of your garden. Blue, forget-me-not-like flowers appear above shimmering silver leaves in late spring. Growing 12 to 16 inches (30 to 40 cm) tall and wide, ‘Looking Glass’ is hardy to Zone 3 and is both deer and rabbit resistant.
‘Ice Dance’ sedge (Carex ‘Ice Dance’)
This bright, variegated Japanese sedge is too rambunctious for the average herbaceous border, but dry shade will keep it within bounds. Deer resistant and hardy to Zone 5, it’s essentially evergreen, although some trimming may be required in spring. Growing 10 inches (25 cm) tall by 18 inches (45 cm) wide, it spreads by underground stolons (runners); mature clumps can be divided in spring.
Red barrenwort (Epimedium x rubrum)
The leaves of red barrenwort, a cross between the European E. alpinum and the Asian E. grandiflorum, emerge in spring with a conspicuous red tinge that gradually turns green and finally takes on a reddish bronze hue in autumn. Cut stems back to the ground in late winter to better appreciate its red-and-yellow-striped flowers in spring. Growing 12 inches (30 cm) tall by 18 inches (45 cm) wide and hardy to Zone 4, red barrenwort is deer and rabbit resistant.
‘Bevan’s Variety’ bigroot hardy geranium (Geranium macrorrhizum ‘Bevan’s Variety’)
Masses of deep magenta-pink flowers are produced in early summer and held above aromatic, downy green foliage that turns cranberry red in autumn. Native to Europe, bigroot geraniums grow 12 inches (30 cm) tall by 18 inches (45 cm) wide, and form a dense mat capable of choking out most weeds. Deer and rabbit resistant and hardy to Zone 3, plants can be divided in early spring or fall.
Hellebore (Helleborus x hybridus cvs.)
Probably due to the price of new cultivars, gardeners tend to treat hellebores with kid gloves, apparently forgetting what tough old customers they actually are. Once established, hellebores self-seed to form large colonies that are particularly well suited to growing in dry shade. Hardy to Zone 4 and growing 16 inches (40 cm) tall and wide, hellebores are deer and rabbit resistant.
Variegated Solomon’s seal (Polygonatum x hybridum ‘Striatum’, syn. P. multiflorum ‘Variegatum’)
A marvellously architectural plant, variegated Solomon’s seal has graceful arching stems with green leaves edged and streaked with white, and dangling, white, bell-shaped flowers in late spring. Growing 24 inches (60 cm) tall by 18 inches (45 cm) wide and hardy to Zone 3, it takes a few years to establish, and then spreads slowly but steadily by underground rhizomes; deer and rabbit resistant.
‘Sissinghurst White’ lungwort (Pulmonaria ‘Sissinghurst White’)
Another terrific plant for lighting up dark corners, ‘Sissinghurst White’ has deep green leaves spotted with silver and bears clusters of pristine white bells in mid-spring. It grows 10 inches (25 cm) tall by 18 inches (45 cm) wide and spreads slowly via creeping roots; self-seeds modestly. Hardy to Zone 3, its deer- and rabbit-resistant leaves can be cut back hard if they begin to look tatty by midsummer; mature clumps can be divided in autumn.
8 great groundcovers for dry shade
Given plenty of moisture, these tough-as-old-boots groundcovers can easily become invasive, but grown in dry shade, they will be far less unruly. Plants will require supplementary watering for one year while they become established.
[Common and botanical name / Hardiness zone / Dimensions (height x width)]
Lily of the valley (Convallaria majalis) Zone 2, 6 x 12 in. (15 x 30 cm) Considered invasive in some jurisdictions.
Sweet woodruff (Galium odoratum) Zone 3, 4 x 12 in. (10 x 30 cm) Considered invasive in some jurisdictions.
Spotted deadnettle (Lamium maculatum cvs.) Zone 3, 6 x 12 in. (15 x 30 cm)
False Solomon’s seal (Maianthemum racemosum) [syn. Smilacina racemosa] Zone 3, 24 x 24 in. (60 x 60 cm)
Ostrich fern (Matteuccia struthiopteris) Zone 2, 36 x 36 in. (1.2 x 1.2 m)
Japanese spurge (Pachysandra terminalis) Zone 4, 8 x 12 in. (20 x 30 cm)
Lesser periwinkle (Vinca minor) Zone 3, 4 x 24 in. (10 x 60 cm) Considered invasive in some jurisdictions.
Labrador violet (Viola riviniana [Purpurea Group], syn. V. labradorica) Zone 3, 4 x 6 in. (10 x 15 cm)