Landscapers are looking beyond conifers to these trees offering year-round foliage, flowers, drought tolerance and cold hardiness.
In looking at a rooftop garden in downtown Portland, Sean Hogan saw something that caught his eye. There, some 20 stories up, he saw several Acer rubrum (red maple) trees. All had changed to their fall color — several months early.
“It’s strange,” said Hogan, owner and principal designer of Cistus Design Nursery in Portland. “Visitors come to Portland in summer and scratch their heads at the beautiful fall color — in June.”
The cause? A stress reaction caused by drought conditions.
Along with others in the industry, Hogan believes that broadleaf evergreens could be the answer in Pacific Northwest landscapes both public and private. These trees and shrubs can handle local climates, while providing the landscape with specimens that recognize the region’s unique botanical character.
Hogan wrote about the idea in Trees for All Seasons: Broadleaved Evergreens for Temperate Climates (Timber Press, 2008), and he’s not alone in his thinking.
Increasingly, broadleaf evergreens are being recognized for their capability to not only be climate appropriate, but also to hardily handle climate change and provide the characteristics the retail market is looking for in its plants, including four-season interest and flowering.
“Gardeners are shifting to work with nature, rather than against it, and to gardens that are sympathetic to where they live,” said Jen Hardin-Tietjen, general manager at Forestfarm in Williams, Oregon. “I think that is a reason to find lush-looking plants.”
Broadleaf evergreens don’t fit the traditional xeriscape garden, but they’re appealing because of their drought tolerance.
Oregon nursery growers must watch the bottom line, however. The East Coast and Midwest markets that make up the bread-and-butter clientele for many Oregon growers are filling their sales order forms with deciduous trees and conifers.
“If you look at the statistics for Oregon, the [nursery] product that leaves Oregon is well above 70 percent,” said Jay Sanders, sales manager at KG Farms in Woodburn, Oregon.
As a result, native nurseries and specialty nurseries tend to be more successful at selling to the Pacific Northwest, Sanders said.
Also suppressing demand for broadleaf evergreens is the fact that many are USDA Zone 8, making them less suitable for colder markets. There’s also the expense of growing them. Some of the more popular ones take much longer to grow to specimen size.
Forestfarm, with its mail-order business, sells a constant supply of broadleaf evergreen trees, Hardin-Tietjen said. However, the specialty grower stops at a 5-gallon size, putting the task of growing to a larger size onto the consumer.
Seattle-based landscape architect Michael Lee summed it up thusly: “Nurseries will only grow what they can sell, and landscape designers will only spec what they can buy,” he said.
Still, Pacific Northwest and other large markets, wholesale and retail, increasingly value the qualities that broadleaf evergreens bring to the table.
“The East Coast is a big market, but we have lots of places that have a strong market (for trees outside those colder, wetter zones),” Hogan said.
Many markets marked by periods of drought or summer drought are searching for trees that will maintain their foliage and thrive in these conditions. Hogan said that nurseries should consider growing a percentage of their plants for these other markets.
Supply right now is consistently low for plants that are in constant demand, according to Lee, Hogan and Hardin-Tietjen. They and others have either been in the position of collecting seed to grow varieties in demand, growing out broadleaf evergreen trees to size for landscape jobs, shipping from California, or having to discontinue offering or specing broadleaf evergreen trees when availability in the region dries up.
But the desire for consumers and commercial properties to find broadleaf evergreen trees, many times native types, that will be more climatically appropriate is a constant these days, providing opportunities for growers to assess the possibility, especially with new breeding programs, of meeting demand that some say will only increase.
The great oaks
Oaks (Quercus), with several hundred evergreen varieties from shrubs to large trees, are one category receiving a lot of attention for their ability to handle a variety of landscaping needs.
For practical purposes, they are deep-rooted, evergreen and suited to growing for extended periods without water.
“For me, they don’t make us look like Detroit in winter, with so many dismal deciduous trees,” Hogan said.
For landscape value, their many forms answer the need for plants that perform well, have interesting leaf color and year-round interest, and “don’t look like oaks,” Hogan said.
The commonly held perception of the oak-tree leaf form is based on widely planted types, such as red (Q. rubrum), pin (Q. palustris) and scarlet oaks (Q. coccinea). But many evergreen oaks are either grown in California or available in only 2–5-gallon sizes that must be grown bigger for larger installations.
Among the favorites:
- By far, cork oak (Q. suber) was mentioned as receiving huge interest regionally that is met largely by imports from California. A Mediterranean tree, it grows to 65 feet. It has a thick and knobby bark that owns the distinction of being able to regenerate itself once peeled from the tree, revealing a deep orange underside. Leaf form is shallowly lobed, looking more like a cottonwood than an oak.
- Canyon live oak (Q. chrysolepis) is native to the western United States. It is a deep-rooted tree with a golden underside to its leaf, and at 30–50 feet, it is useful where a smaller mature tree for public installations is desired.
- Silver oak (Q. hypoleucoides), now on Portland’s street tree list, has silver bark and a narrow leaf with an attractive reflected white underside. “It’s a nice size, not too big, reaching 30 feet or so,” Lee said, “with beautiful texture and is totally hardy. It’s very drought tolerant, but because it comes from a monsoon area, it will be fine with water.”
- Interior live oak (Q. wislizeni), which Hogan used at Portland’s Edith Green-Wendell Wyatt Federal Building, can reach 50 feet with glossy, oblong, dark green leaves.
- Laurel oak (Q. laurifolia) is on beautiful display in Seattle’s Washington Park Arboretum and around the city. They have bright green foliage that stays nice in winter, even as they can thin out. Growing 65–80 feet, they can withstand wet or dry conditions, growing anywhere you plant it, Lee said.
On the smaller side
Obviously, the limitation for home-owners growing oak can be the large size.
“What we’re hearing from consumers is city lots are getting smaller,” Hardin-Tietjen said. “In general, any of the cultivars coming out that are smaller or columnar, that fit more into garden spaces, we snap up right away.”
One of the shorter varieties, Mexican blue oak (Q. oblongfolia) is shrubbier with small oval and powder blue leaves, pink-red new growth, and it grows only 20–30 feet, Hogan said.
Also being used in smaller gardens are many large shrubs that grow to the height of a small tree.
For instance, strawberry bush (Arbutus unedo), a popular seller at Forestfarm for its dwarf habit and hardiness in wide-ranging water situations, fits the need for evergreens in small spaces. “Wherever you can get evergreen more dwarf, you will be more successful,” Hardin-Tietjen said.
For the love of a flower
Sweetbay magnolia (Magnolia virginiana) makes a nice street tree for its fragrant flowers, Lee said. It has forms that are less evergreen and others that are more so. On the more evergreen side are ‘Moon Glow’, which is slow-growing to 15 feet over 10 years, and ‘Henry Hicks’, with its columnar habit.
“They tolerate wet or dry conditions and blend with everything,” Lee said.
M. virginiana var. australis is, in general, more evergreen and more drought tolerant and much deeper rooted than the semi-deciduous ones that are more commonly grown, according to Hogan.
Also in the smaller tree category, Michelia maudiae, an import from China, reaches 25 feet over 10 years, but blooms young with flowers along the preexisting leaf axles in late spring through May, contrasting the bluish leaf. “They need some summer irrigation, but they’re very useful as a small street tree or for a garden and patio,” Hogan said.
M. laevaefolia can be shrubby or grown to a dwarf-size tree. It has copper-colored indumentum on stems, leaves and buds, and abundant, fragrant flowers in late spring and fall.
Evergreen dogwoods also fit into the small trees category homeowners want, and they answer the call for flowers. Hogan split dogwoods into two categories: those that are highly drought tolerant, and those that take nurturing and some periodic summer irrigation.
“These are trees that can survive with little or very little irrigation, and are adapted to dry weather,” Hogan said.
For instance, Cornus capitata ‘Mountain Moon’ produces abundant flowers even in dry heat. Lee recommended C. capitata ‘Summer Passion’ for its spate of small flowers in spring and early summer, followed by shiny leaves that emerge in a purple-bronze color through most of summer.
And then there is the category that needs some summer irrigation but has tremendous flower power, such as C. kousa var. angustata, with its star-shaped flowers and dark green narrow leaves, and C. omeiense, with its glossy foliage, coppery-bronze new growth and large flowers.
“Both are Zone 7,” Hogan said, “and 20-footers that flower well into summer.”
When clients are looking for that tree they hope will hide the neighbors’ garage, and they were thinking of birch, Lee turns to boxleaf azara (Azara microphylla), which is readily available. It will shield the view of the ugly garage much better than the birch, and it will provide flowers to boot, followed by small berries.
“It’s useful for screening and has a light texture, filmy not heavy,” Lee said.
“One issue with evergreens, especially in tree forms, is a lot of them are Zone 8, and we’re a Zone 7,” Sanders said. “It depends on their zoning, whether you see them in a nursery.
“As our zones change with the onset of warmer weather, that does open the door for the production for some of the less cold-hardy plant material.”
At the same time, breeding programs are creating more cold-hardy plants, Sanders said; for instance, taking old-fashioned varieties like M. grandiflora and yielding ‘Victoria’ and ‘Little Gem’ to tolerate Zone 7.
“Eucalyptus is a strong Zone 8 tree, but that being said, if it’s planted in the appropriate environment and drainage in Pacific Northwest, it will actually survive, except for extremely cold years, when you may see some dieback,” Sanders said.
Hardy varieties being grown in the Pacific Northwest include Eucalyptus lacrimans (weeping snow gum), which has “a stunningly beautiful, smooth, creamy gray-covered trunk with weeping foliage,” Lee said. “You expect to see it in Los Angeles, but it’s probably the hardiest eucalyptus around here. It’s not big, growing to 30 feet or so, and it’s a beauty. During the cold snap a few years go, the one in a front yard not far from my house had no damage whatsoever.”