Best Plants Under Big Trees

Below the canopies of mature trees lies a double gardening whammy: thick shade and parched ground. Plants must not only battle for sunlight, but also compete with tree roots for water.Because tree roots can extend as far out as the branches, anywhere within the drip line (the ground area under the tree's outermost branches) is the dry-shade zone. It's hard to improve soil here, as you don't want to damage the tree roots. Even plants that like shade, such as primroses, moss and ferns, can struggle without extra care.But by choosing the right plants--such as hostas, pictured at left--you can have a lush green undergrowth. Read about our recommendations on the next six slides.

Use at least a 3-inch layer of mulch to conserve soil moisture around new plantings, says Matt Fox, horticulture manager at the Iowa Arboretum (30 miles northwest of Des Moines near Madrid).Keep mulch an inch away from tree trunks so it won't smother the tree roots or introduce pests or disease. Any new plantings should go at least 1 foot inside a tree's drip line.Dry-shade-tolerant plants need extra water their first summer and fall, but then should survive with little added moisture except in extreme drought.An easy, common plant for dry shade is Vinca minor (left). It spreads quickly and looks attractive, with glossy leaves and purple-blue flowers.Other interesting possibilities for dry shade include hostas, Canadian wild ginger, fringed bleeding-hearts, 'Pink Skyrocket' foamflower and 'PJM' rhododendron (details on next slides).

Hostas These leafy perennials love the shade and come in many foliage variations. Good choices include 'Pandora's Box' (green-edged, white leaves, 8 inches tall); 'Francee' (white-edged, olive green leaves, 2-3 feet); 'Frances Williams' (pictured at left; blue-green leaves with chartreuse edges, 2-3 feet); and 'Guacamole' (dark green-edged gold leaves, up to 3 feet). Many hardy to Zone 3.

Fringed bleeding-hearts (Dicentra eximia or Dicentra 'King of Hearts') Unlike spring-blooming bleeding-hearts, which go dormant by summer, the flowers and blue-green, fernlike foliage of fringed bleeding-hearts (left) persist through the season. They grow up to 2 feet tall. To Zone 4.

'Pink Skyrocket' foamflower (Tiarella cordifolia) 'Pink Skyrocket' (left) features serrated, maplelike leaves with bronze veins and, in spring, dense, 11-inch spikes of fragrant pink blossoms. To Zone 3.

Canadian wild ginger (Asarum canadense) This easy-care, 4- to 6-inch-tall perennial groundcover (left) survives in harsh climates and spreads easily. Rounded, heart-shape leaves grow 2-4 inches long. To Zone 2.

'PJM' rhododendron (Rhododendron 'PJM') An understory shrub that grows up to 4 feet tall and wide, 'PJM' is one of the few rhodos that grows well in the alkaline soil common in many parts of the Midwest. Clusters of lavender flowers stand out against shiny, dark green leaves. To Zone 4.Pictured: Rhododendrons flourish under trees at the Holden Arboretum in Kirtland, Ohio.