Gardening under a tree can present challenges, but with careful planning you can create a peaceful place to relax that also shows off your green thumb. Include elements other than plant material to round out the space -- a birdbath, comfortable seating and a small water garden are inviting additions. Common shade-loving plants don’t always sport colorful blossoms as their major point of interest. Colorful foliage is longer-lasting than flowers, and textured leaves and shapely plants add interest all season long.
If you are gardening under a mature tree with canopied top growth, plant native understory trees such as dogwood or redbud. Local, native woodland plants that grow successfully in your climate are good choices for mid-level and ground cover plantings. Try to maintain the grade of the land surrounding the tree: Don’t build up the soil into a raised bed or otherwise raise the grade around the trunk or bury exposed roots. Doing so can cause stem-girdling roots or trunk rot to develop. Set new, small plants no closer than 12 inches to the trunk, and if you encounter tree roots as you dig planting holes, relocate the new plants and leave the tree roots undisturbed. As options to in-ground plantings, potted flowering plants placed on natural moss enhance the space with little effort. While you may not think of them for a shade garden, hanging baskets add color and texture. Place them on tall shepherd crook hangers for eye-level appeal.
Different tree species have different root structures. For example, nut-bearing hardwoods tend to have deeper roots and fewer fibrous surface roots, while other deciduous trees may have extensive feeder root systems that spread close to the surface under the tree. Small amounts of root damage can cause progressive tree-health issues, even for a large, established tree. Dig carefully under a tree, and avoid using a tiller where the roots are close to the surface. Instead, dig with hand tools or a spading fork, identifying and protecting the root structure as you work. Set permanent plantings in the spaces between roots, especially creeping or spreading vegetation that will become a ground cover. Horticulture experts at the University of Illinois suggest planting under a tree one section at a time over a period of a few years to limit shock to the tree.
Shade density under a tree varies depending on the tree species, the season of the year, the time of day, and surrounding undergrowth. Dappled sunlight under an open, branching tree can be utilized by planting shade-loving shrubs such as peegee hydrangea (Hydrangea paniculata) or bigleaf hydrangea (Hydrangea macrophylla) as a middle layer, creating denser shade for low-growing flowers and plants at ground level. Species of hydrangea vary in cold hardiness: Peegee varieties are generally hardy in U.S. Department of Agriculture planting zones 3 through 8, while bigleaf varieties tolerate warmer USDA zones 6 through 9. You can alter the perception of light under a tree by incorporating plants such as yellow-leaved hostas (Hosta ‘Bright Lights') for brightness, or a dark-leaved hosta variety such as Blue Shadows (Hosta 'Blue Shadows') to deepen the perception of shade density. Most varieties of hostas are perennials in USDA zones 3 through 8, with many varieties tolerating sheltered, moist areas of zone 9.
Trees monopolize water and nutrients in the soil, and they steal the nutrients from new plants you place in the ground near their roots. Plan to irrigate a garden under a tree and increase the fertilizer schedule as necessary. Shrubs and perennials can take three years to become well-established, and they may need extra attention during that time. Planting in containers allows you to properly care for individual plants with different needs. You can arrange and rearrange container placement to highlight certain plants when they look their best.