Some Like It Dark
Despite the reputation of conifers as sun-loving plants, there are selections that do well in shaded areas of the landscape, as well.
Shade is to plants what SPF is to human skin. Higher levels of SPF in sunscreen give more protection from the sun's rays. Many plants are protected from the sun for part of the day, but get full sun for the rest. Others experience light shade under the umbrella of a tree with only occasional sunlight peeking through the leaves. For those places where very little light filters through, the plants receive considerable protection from the sun. Plants in this situation are considered to be in full shade.
A Japanese tree commonly found growing in shady locations, Thujopsis dolabrata is perfectly adapted to low-light sites. A slow growing large tree, it can be quite elegant with sprays of bold foliage. Top left, the unique foliage of Thujopsis dolabrata is highlighted by chalky white variegation.
Photos courtesy of U.S. National Arboretum unless otherwise noted.
Chances are good that you've encountered this situation all too often; so many landscape sites present the puzzle of what to plant in shade. And for the client who's eager to have conifers, it's a tricky call. Conifers don't usually jump to mind as options for these sites, especially since we tend to think of all conifers as sun-loving. While that's mostly true, there are a number of selections that actually grow well in shade. In fact, some require this natural form of "sunscreen" for survival.
In general, solid green colored conifers are the best performers in shade. They put all of that chlorophyll to good use for food production, which keeps them strong and vibrant in the lower light levels. On the other hand, variegated conifers and those conifers from more northerly climates do well in light or filtered shade. Note that we say "light or filtered" shade-not full shade. If the shade becomes too dense, the variegation that's the highlight of these selections will fade over time.
And as much as your clients would like to brighten up that dark spot in their shady conifer garden with gorgeous golden or yellow varieties, these conifers really aren't made for the shade. Planting them in a shady area will most assuredly cause them to lose that vibrant, sunny color.
If you're designing for a client whose site has a "dark side," here are some of the best conifer selections for shady places.
Taxus is one of the best conifers for those dense shade areas, and the variety available means there's sure to be a yew for every shady garden. The foliage is generally very dark green, and female selections will have red, fleshy fruits, or arils. Growth habits range from low and spreading to narrow columns and large pyramidal trees.
If the site calls for a short, neargroundcover plant, try T. baccata 'Repandens', a low-growing selection with arching branches that droop slightly at the tips. If allowed to spread naturally, the plant reaches nearly 10 feet wide and grows only to about 4 feet in height in zones 5 to 9.
For a shady site that needs a focal point, there's T. × media 'Flushing', which has a narrow, columnar habit. While 'Flushing' can reach 12 to 15 feet in height, it spreads to only 2 to 3 feet in zones 4 to 7.
A fastigiate form of Taxus baccata makes an outstanding focal point in the shade garden.
And if you're fortunate to be working on a shady site that can support a larger tree, T. × media 'Kelseyii' is a good choice. Kelsey yew can grow to about 15 feet at maturity, with a spread of 10 feet in zones 4 to 9.
A word or two of caution in growing yews: They will not tolerate wet or damp soils and must be planted in well-drained sites in order to thrive. They're also favored by deer, so if the deer population in the area is at critical mass, be judicious with your placement.
Cephalotaxus (plum yew)
Similar in overall appearance to the yew, plum yew's foliage is a little coarser in texture and more olive-green in hue. There are low-growing selections as well as a beautiful, large, wide, spreading shrub.
C. harringtonia 'Prostrata' can be used as a groundcover, growing only 2 to 3 feet in height with a similar or slightly wider spread in zones 6 to 9. Its low, mounding habit features arching, pendulous branches that reach up and out in a delicate-looking-but sturdy- spray.
For a larger selection, try C. harringtonia 'Duke Gardens', a slow-growing plant that reaches 4 to 6 feet tall and wide in zones 6 to 9. The oval to rounded shape is highlighted by upswept, arching branches and can lend a semi-formal look to the shade garden.
Unlike yew, plum yews are much more tolerant of a wide range of soil conditions and are equally adapted to dense shade plantings. Plus, they're relatively resistant to deer pressure and can offer a suitable substitute for Taxus where deer browse is heavy.
Cephalotaxus harringtonia 'Prostrata' can be used as a groundcover, growing only 2 to 3 feet in height with a similar or slightly wider spread. Its low, mounding habit features arching, pendulous branches that reach up and out in a delicate-looking-but sturdy-spray.
Thuja occidentalis and T. plicata
Both Thuja occidentalis (American arborvitae) and T. plicata (western red cedar) are native conifers and are extremely adaptable plants. Both species have many cultivar selections that vary in color and habit. Tolerant of damp or dry soils, they require filtered sun or high shade to survive.
An old cultivar, Thuja occidentalis 'Hetz Midget', as the name implies, is a dwarf form with rich green foliage. It grows slowly to 3 feet tall. The cultivar 'Little Gem' forms a dense globe with dark green foliage. Many other cultivars grow in light shade as well.
Chamaecyparis obtusa (Hinoki false cypress)
Well-known for their beautiful sprays of cupped, dark-green foliage, Hinoki cypress are slow growers that need moist, well-drained soils. Plants grow well in light shade or on sites that have afternoon shade, especially in the summer months.
What do we mean by "shade"?
Definitions of sun requirements may vary from region to region and from horticulturist to horticulturist, but most can agree that few plants do well in 100 percent, never-see-the-light shade. Mushrooms, maybe, but not ornamental plants. But what is really meant by "shade"?
In general, here's the scoop:
Full sun: Six or more hours of direct sunlight each day.
Partial sun/partial shade: These terms are often used interchangeably, but there's a subtle difference. Many hold that "partial sun" means 4 to 6 hours of sun each day, and "partial shade" is slight less: about 2 to 4 hours of sun each day.
Filtered sun/dappled sun: Also called filtered shade and dappled shade, these terms indicate that light is available through the canopy of an overstory plant.
Full shade: Less than 2 hours of sunlight each day.
Then there are "light shade," "deep shade," "thin shade," "dense shade" . and the list goes on. When in doubt, ask the grower or your extension agent.
C. obtusa is a large plant, growing 50 to 75 feet in height and 15 to 25 feet wide in zones 4 to 8. It has a pyramidal habit, featuring spreading branches that tend to droop a bit at the tips. On mature trees, the reddish brown bark peels, providing an additional textural interest.
Smaller, more landscape-friendly cultivars have been developed; for example, C. obtusa 'Nana Gracilis' reaches only to 3 to 6 feet and spreads about 2 to 4 feet in the first 10 years, obtaining 6 to 9 feet in height at maturity. C. obtusa 'Green Cushion' is a miniature selection, growing only about 1 inch per year.
Chamaecyparis obtusa 'Green Cushion' is a miniature selection, growing only about 1 inch per year.
Thujopsis dolabrata(hiba cedar)
A Japanese tree commonly found growing in shady locations, Thujopsis dolabrata is perfectly adapted to low-light locations. A slow growing large tree, it can be quite elegant with sprays of bold foliage.
Thujopsis dolabrata 'Nana' is a compact, slow-growing selection has unusual, antler-like foliage with pronounced, chalky white undersides. Over time, the plant forms a layered mound, reaching 4 feet in height with a 6-foot spread in zones 5 to 9. It does best in filtered shade.
Tsuga canadensis(Canada hemlock)
Commonly seen growing on moist, north-facing slopes in its native range, hemlock has adapted well to garden situations. There are weeping selections, dwarf, congested foliage selections, and the more familiar graceful pyramidal shaped plants. They do well in filtered sun and can tolerate occasionally dry soils once they are established.
Thuja occidentalis 'Hetz Midget', developed and grown by Fairview Evergreen Nurseries, is a compact plant that grows to about 3 feet tall and wide.
Photo courtesy of Hagan Hetz, Fairview Evergreen Nurseries
However: As good a plant as Canada hemlock may be, the Eastern half of the U.S. has experienced significant problems with hemlock woolly adelgid (Adelges tsugae), and so we no longer recommend this plant for landscapes east of the Mississippi River.
Susan Martin is the former curator of the U.S. National Arboretum's conifer collection in Washington, D.C.; she retired in 2007 after 30 years in her position. Chris Carley is supervisory horticulturist for the U.S. National Arboretum. He can be reached at Christopher.firstname.lastname@example.org.