MADE FOR THE SHADE (continued from The Vine newsletter)
Perfect Perennials for Dry Shade Gardening
by Pam Beck
Shade, like the saying about death and taxes, is inevitable for serious
gardeners. Either we choose to live in a house on a heavily wooded lot graced
with towering trees, or, more boldly, we move to an open, sunny space and
immediately begin planting woody specimens.
Our love affair with maturing tall trees and the dark, cooling shade they cast presents one of gardening’s greatest challenges.
Gardening books are frequently unclear about plants that grow well in shade, simply because the
definition of shade is ambiguous. We would all agree that the heavy veil cast by the
solid wall of the north side of a two-story house or privacy fence is total, deep shade, but
what constitutes bright, dappled, or partial shade? How many hours of gentle morning
sunlight equal a couple of hours of intense afternoon baking for a partial shade perennial?
If the filtered dancing shadows of pines are somehow less dense than the gloom of oaks
and poplars, which of the two is low light?
When selecting plants at a garden center, tell me who the
horticulturalist is who determines whether the plant label reads “part sun” versus “part shade,”
or distinguishes between “shade-loving” and “shade-tolerant?” And, why are the
perennials we traditionally grow in shade in the Southeast often listed as perfect for “full
sun” sites in the British Isles. That is the ultimate oxymoron! It seems the only way to prove a plant’s true worth in
shade is to plant it in at least three places around the landscape.
Added to the trials of choosing the right plants for limited
sunlight is the fact that the sheltering overhead canopy works much like an umbrella
deflecting rain. The most arid spot in any garden is at the base of spreading
evergreens and mature, large-leaved trees. Any moisture that finally does hit the ground is greedily taken up by
aggressive tree roots, leaving little for understory plants. Overbearing oaks,
sweetgum and maples, sycamores, birches and beeches are all notorious for their thirst.
A massive southern magnolia’s root system can stretch across the width of its
canopy and beyond, requiring gallons of water a day. So it is little wonder that even
weeds don’t volunteer under these evergreens.
Even during years of abundant rainfall, dry shade is still a given. We won’t mention
those horrible years of drought. But, don’t despair, rev up your chainsaw to clear cut your
woodland, or install irrigation lines just yet! A surprising number of adaptable
perennials not only survive in dry shade, but will happily thrive there, too.
Some years ago, I interviewed an expert on gardening
in dry shade in the Southeast, W. George Schmid, author of An Encyclopedia of
Shade Perennials and The Genus Hosta, both published by Timber Press. Schmid, who
hails from Bavaria, attended the University of Munich, where he studied
architecture, horticulture, botany, and landscape architecture. After a career in
these fields, he retired to dry shade gardening in his own
personal landscape outside Atlanta, GA.
Recommending perennials for the dry forest floor, Schmid admitted, “Dry shade
is a tall order. First, how dry? Like four years drought, or normally dry? Even hostas croaked
here due to drought.”
Of the true dry shade survivors, Schmid advised, “Not surprisingly, most are
natives and many have fleshy, underground rhizomes. Fleshy root systems always
contribute to drought resistance.” He recommended wild leek Allium; Anemonella (rue
anemone); native Asarum (wild gingers); Chimaphila maculata and C. umbellata better
known as Pipsissewa; Galax; dwarf crested Iris cristata; Mertensia virginica (Virginia
bluebells); Pachysandra species; and, Tiarella (foam flower). “I lost none of these during
our drought,” said Schmid. (See the sidebar for his complete list.)
Since I garden just north of Raleigh, N.C., in a 60-year old
deciduous forest formerly farmed for corn (producing moonshine before my
time), and I don’t irrigate, the shade plants I grow either survive or are replaced with
more drought-tolerant selections. To Schmid’s list, I would add my own
success with Ajuga (bugleweed); Arisaema triphyllum (Jack-in-the-Pulpit); Arum
italicum ‘Pictum’ (Lords and Ladies); Athyrium nipponicum (Japanese painted fern);
various Cyclamen for winter interest; Euphorbia amygdaloides var. robbiae (Mrs. Robb’s
euphorbia) aggressively spreading even in the driest spots; Japanese rooftop Iris
tectorum; Oxalis regnellii ‘Triangularis’ (purple shamrock); naturally occurring
evergreen Polystichum acrostichoides (Christmas fern) and its cousin from Asia
Polystichum polyblepharum (tassel fern); and, our native Trillium.
If I had to choose one reliable perennial for dry shade that I wouldn’t be without,
it would have to be the pale blue fragrant woodland phlox indigenous to
eastern North America, Phlox divaricata.
Most low light, drought-tolerant perennials still require adequate water while
getting established. If you can care for them faithfully throughout the first year, also try
the native sky blue star Amsonia tabernaemontana; pink and white Japanese Anemone x
hybrid; reliable Begonia grandis (hardy begonia); the dainty springtime Erythronium
(trout lily); Ophiopogon (mondo grass); and, all colors of Tradescantia (spiderwort).
Eventually, you should be able to allow the following ferns to make it on their
own, too. Plant the nearly indestructible and aptly named Polypodium polypodioides
(Resurrection fern); shiny dark green Cyrtomium falcatum (holly fern); and, the
evergreen bronze-tipped Dryopteris erythrosora (autumn fern).
Spring flowering bulbs are essential additions if you are gardening under
deciduous trees. Since direct sunlight will hit them before the canopy completely fills out,
underplant dry, shady areas with sweeps of colorful crocus; cheerful daffodils; Ipheion
(starflowers); Leucojum (snowflakes); various Muscari (Grape Hyacinth); Scilla; and
returning species tulips.
The first rule of planting perennials, or any other understory plants, in the shade
of large trees is to do everything possible to preserve their roots and avoid
damage to them. Never till the area under a large tree. It would be better to use a
narrow shovel or hand spade, gently working around support roots as you dig. Don’t
completely encircle a large tree with new plants all at once, possibly damaging roots all
around. Remember that small holes are preferable to large ones, while still making the
width of the planting hole twice the size of the perennial’s rootball.
Another advantage of buying smaller plants is that you will save money, allowing for more
There is an ongoing debate over the value of soil amendments when
underplanting large trees. The answer depends on your soil type. Schmid advised,
“Most woodlands do not have sandy soil except along the coast. In garden woodlands,
organic matter must be added to sand or all bets are off.” On the other hand,
“Clay absorbs lots of water, but once dry, takes forever to get moist again.” The best way
to deal with clay-based soils is to fill in with the best soil you can find on the premises
Importantly, soil should never be piled around trees to raise a
bed for planting. Additional soil covering the trunk and support roots makes a fine home for insects
and disease, and if soil is piled over feeder roots,
oxygen and water cannot be absorbed.
The same is true with mulch. Whether pine needles, bark mulch, or composted
leaves, mulch is best kept away from the tree trunk and only applied to a depth of
two to four inches inside the dripline.
Finally, watch for continuous falling twigs and branches,
pine needles that pierce your hosta leaves like arrows, and acorns that can beat down like
hail. A clever way of dealing with these menaces is to plant
understory dry shade-tolerant shrubs and small trees to help protect your perennials. The
additional height will add to the overall beauty of your woodland garden.
For a detailed definition of the varied aspects of shade, and for an extensive list of
shade-loving perennials, refer to An Encyclopedia of Shade Perennials, by W. George
Schmid, 2002, Timber Press, hardcover $49.95, ISBN 0-88192-549-7.
George W. Schmid’s list of favorite perennials for dry shade:
Allium (wild leek)
Anemonella (rue anemone)
Aquilegia canadensis (columbine)
Asarum all natives (wild gingers)
Aspidistra sp (cast iron plant)
Asters (wood aster)
Campanula divaricata (bellflower)
Carex sp (sedges)
Chimaphila maculata, umbellata (Pipsissewa)
Chrysogonum virginianum (green and gold)
Claytonia lanceolata (mayflower or spring beauty)
Dentaria sp (toothwort)
Disporum sp also exotic sp. (fairybells)
Epimedium sp (barrenwort)
Eupatorium (bone-set or Joe Pye weed)
Galax sp (wandflower)
Geranium maculatum, oreganum (wild cranesbill geranium)
Hieracium venosum (rattlesnake weed)
Helleborus sp (Christmas or Lenten roses)
Heuchera villosa (alumroot or coral bells)
Iris cristata, douglasiana (dwarf crested iris)
Liriope sp (lilyturf aka monkeygrass)
Maianthemum canadense, dilitatum (mayflower)
Mertensia virginica (Virginia bluebells)
Pachysandra sp (spurge)
Podophyllum peltatum also exotic sp. (Mayapple)
Polygonatum sp native and exotic (Solomon’s seal)
Pulmonaria sp (lungwort)
Rohdea (sacred lily)
Sanguinaria canadensis (bloodroot)
Saxifraga sp (mother-of-thousands, strawberry begonia)
Sedum ternatum, nevii (stonecrop)
Silene stellata (campions)
Smilacina sp. (false Solomon’s seal or Solomon’s plume)
Solidago caesia, curtisii (goldenrod)
Tiarella sp (foamflower)
Tricyrtis sp (toad lily)
Trientalis borealis (starflower)
Uvularia sp (bellwort)
Vancouveria sp (inside-out flower)
Vinca minor (periwinkle)
ntinued from The Vine newsletter)