Gardening in the shade is one of the larger challenges that most gardeners face sometime – if not today, then eventually. Landscapes and gardens evolve; change is the norm. Roses and coreopsis that flowered profusely in a young garden become spindly and barren as trees mature. Hostas diminish as an oak tree’s roots invade its space. Different plants suit now-shadier sites.
Gardeners, too, change. Perhaps your heat tolerance is less than when you were 30, or the dermatologist has given you the talk about avoiding direct sunshine. Perhaps the increasingly shady garden is doing you a favor.
What kind of shade?
Every chapter and talk about shade defines shade variations:
Part shade is usually considered three to six hours of direct sun in the morning or late afternoon with solid shade the rest of the time, or continual dappled shade provided by a high tree canopy.
Light (thin) shade describes a location with a couple of hours of morning or late-day sun that is otherwise shaded by immature trees or high tree branches.
Medium or high shade is just a bit dimmer, with more solid tree canopies covering the plants and only a bit of daily sunshine.
Full shade or heavy shade – well, you get the picture. Few situations perfectly match the definitions, and you’ll have to analyze each site carefully – not just in June but later in the season as well. Horticulturists can guide you, but ultimately you’ll have to experiment with the many possibilities among shade plants.
Consider the underground
If shade were merely a function of light intensity, plant selection would be simple. But most shade is caused by trees, and all trees have roots – in fact roots that generally occupy the top 8 inches of soil and grow much farther outward than the trees’ widest branches. So any plants within a tree’s sphere of influence have to compete below ground for water, nutrients and just plain space. No wonder the hosta weakens and the astilbe turns puny as the young oaks and maples attain maturity. This kind of shade – usually called dry shade – is the most difficult place for shrubs or perennials to inhabit, and requires careful plant selection and site manipulation.
In a recent program on shade gardening, hosta expert and author Mike Shadrack described his struggle in a woodland garden: “I dug careful planting holes among the tree roots and used ample compost, knowing that naturally the roots would encroach – but I planned to recut a circle around every hosta every year, to foil those roots. But the garden is enormous and that job never quite gets done. I’ve found that hostas and other perennials near trees seem to do well for three years or so and then seem to stop growing– or even get smaller. Time to dig them up, tease out the tree roots and replant them.”
Plants that require moist soil suffer the most in competition with tree roots. An astilbe in the shade of your house might do twice as well as an astilbe under a tree, given the exact same amount of light. Provide moist soil or don’t bother with astilbes (or Rodgersia, Sanguisorba or Ligularia for that matter).
Right plants for dry shade
Setting the moisture lovers aside, many perennials and shrubs are excellent choices for planting under trees. Plants listed here are cold-hardy; heights shown are approximate – many factors intervene. Just remember that all new plantings need good soil (with the correct pH) and ample water while they get established; after that most will be quite drought tolerant.
• Medium to large deciduous shrubs (4–7 feet)
Calycanthus floridus (Carolina Allspice)
Clethra alnifolia (Summersweet), many sized cultivars
Eleutherococcus sieboldiana ‘Variegatus’ (formerly Acanthopanax), sometimes called Five-leaf Aralia. Don’t let the names scare you.
Aralia racemosa (Spikenard)
Hydrangea quercifolia (Oakleaf Hydrangea)
Viburnum – many
• Short deciduous shrubs (2–4 feet)
Rhus aromatica (Fragrant sumac)
Diervillea lonicera (Bush honeysuckle)
Itea virginica (Sweetspire) ‘Little Henry’ (taller cultivars available)
• Evergreen shrubs (Plants marked * need wind protection)
Pieris japonica* (Japanese Pieris)
Perennials (Plants marked ** spread easily)
Alchemilla mollis** (Ladies’ Mantle)
Anthyrium augustum (Lady Fern)
Aruncus dioicus (Goatsbeard)
Many spring-blooming bulbs
Assuming you don’t want to kill the trees providing your shade, remember their needs and the fragility of their root structures when you plant among them. Never raise the soil level more than 4 inches on top of tree root areas, and never let soil touch the tree trunk; start any planting holes several inches away from the trunk. Plant only a few plants around the tree root zone, and let the plants spread out naturally. If you use logs or rocks to enclose a bed, keep it small and limit the weight you apply on top of the tree roots. Avoid putting weight – machinery or even your own – on tree root areas. Keep root areas mulched and use boards to establish limited foot traffic routes.
With careful plant selection and effort you can establish a tranquil, woodland-like, layered planting in the shade, and it may become your favorite place.
Sally Cunningham is a garden writer, lecturer and consultant.