CHOOSE TREES TO SUIT CHANGING ENVIRONMENT
As we continue to live in higherdensity housing, especially in urban areas, there are many issues that affect us and the changing elements.
Urban heat islands are making our cities warmer by 5 to 7 C. The enjoyment of sitting out on our patio or deck is often compromised by the proximity of other people, so privacy is a concern. The sounds of songbirds and the buzzing of bees have been replaced by the noise of traffic and sirens, and we don’t see as many hummingbirds and butterflies flitting about. The recent smoke from the Interior wildfires is an extreme example of the pollution we are exposed to every day.
One of the very best solutions to so many of these urban realities is to plant the right types of trees in strategically important locations.
When I need advice about trees, my go-to person is Nancy Buley, director of communications for J. Frank Schmidt & Son Co. This Boring, Ore., nursery regularly sends thousands of new trees to 17 locations in North America to be evaluated, and they have one of the finest arboretums in the U.S., displaying a wide diversity of trees for appraisal as they grow and mature.
Buley speaks across North America on the evolving role of trees in the landscape. From city and street plantings to rural settings, she is very knowledgeable about the changing requirements for modern trees.
“Today’s trees need to be very tolerant of insects and disease problems, be able to withstand increasing heat and drought issues, as well as being relatively easy to maintain,” Buley says.
With increasing weather concerns, Buley says trees need to have a strong central leader with wide branch angles to create a more open canopy. As a very strong proponent of diversity, she stresses the need for selecting trees that make the urban forest better able to tolerate the potential increase of disease and insect problems.
Planting columnar trees is very much a trend today simply because most people have less space for trees to spread. When you see a very narrow columnar tree, you may wonder how it will provide much shade or privacy, but Buley says most will thicken out to between eight and 15 feet (2.4 and 4.5 metres).
“Crimson Spire” oak (Quercus robur x Quercus alba) is one of Buley’s favourites — a zone 4 tree, it grows up to 45 feet (13.7 metres) tall and 15 feet (4.5 metres) wide, with beautiful fall foliage that stays on during the winter to produce a comforting rustling sound. “Skinny Genes” oaks grow to a similar height but only 10 feet (3 metres) wide. For a more compact oak, “Kindred Spirit” grows 30 feet (nine metres) tall and six feet (1.8 metres) in width. These are just some of the newer, more compact forms that are ideal for planting in more confined areas.
I asked Buley about my favourite columnar Acer rubrum maples, and she was concerned that so many are being planted that diversity could possibly be compromised. She did give a nod to the new Acer rubrum “Armstrong Gold” (45 feet x 15 feet, or 13.7 metres x 4.5 metres) as being one of the better selections and to the broader-growing Acer rubrum “Redpointe” (45 feet x 30 feet, or 13.7 metres x nine metres) as one of the more disease- and heat- and droughttolerant maples that grows in a pyramidal form.
Other columnar trees of note are the zone 5 hornbeams, particularly Carpinus “Frans Fontaine,” which grows only 35 feet (10.6 metres) tall and has a 15-foot (4.5-metre) spread, as well as the columnar forms of the sweet gum tree like Liquidambar “Slender Silhouette” (60 feet x eight feet, or 18 metres x 2.4 metres) or the much more compact L. “Emerald Sentinel” (30 feet x 12 feet, or 9 metres x 3.6 metres). Both these have far fewer seed pods than their much larger cousins. Their disease resistance and drought tolerance are excellent, and their fall colour is delightful.
Planting smaller shade and screening trees is another current trend Buley mentioned. Many have flowers that are hugely beneficial for pollinator populations. Frank Schmidt & Son decided a few years ago to specialize in a selection of smaller trees. They can be more difficult to train when young, but the company could see a great potential for this type of tree.
The zone 4 fringe tree (Chionanthus virginica) is a prime example, growing only 18 feet (5.4 metres) tall with a potential spread of 20 feet (six metres). It has beautiful, clean foliage and fragrant clusters of white flowers in late spring. Buley is particularly proud of a zone 5 variety the company found in Japan called “Tokyo Tower” (20 feet x 10 feet, or six metres x three metres) which provides four seasons of beauty — notably in winter with its interesting, peeling tancoloured bark.
The silverbell tree (Halesia carolina) also rated as zone 5, and is smaller with white bell-shaped flowers. Buley says H. c. “Wedding Bells” is one of the best new cultivars, growing only 20 feet (six metres) tall and 15 feet (4.5 metres) wide, with prolific white bell-shaped flowers.
The Kentucky coffeetree (Gymnocladus dioicus) is a very clean zone 4 tree with double compound bluish-green leaves. The newest variety, G. “Espresso” (50 feet x 35 feet, 15 metres x 10.6 metres) has a nice oval growth habit.
One of my favourites is the zone 5 sourwood tree (Oxydendrum). Pyramidal in form, it grows about 20 feet (six metres) tall and 15 feet (4.5 metres) wide. In late July to August it bursts into bloom with pendulous, creamywhite flowers, and its late summer orangey-scarlet foliage holds nicely into fall.
The new hottie in snowbells is S. “Snowcone,” which grows to 25 feet (7.6 metres) and has an attractive pyramidal shape. Buley also mentioned a new purple foliage variety called S. “Evening Light” that grows only 15 feet (4.5 metres) tall and wide. Its white flowers, contrasting with the purple foliage, are really something special.
As mid-sized flowering trees, the Chinese tree lilacs are becoming very popular. Syringa “Beijing Gold” has beautiful clusters of yellow flowers, and S. “China Snow” has luscious creamy white blooms. Both grow about 20 feet (six metres) tall and 15 to 20 feet (4.5 metres to six metres) wide. Their flowers are spectacular when they bloom in late June and July.
One of the more unusual small shade trees is the Seven Sons plant (Heptacodium miconioides). Although difficult to train into a shade tree because of its multiple stems, once established it is incredibly resilient and drought-tolerant. Its fragrant flowers appear in mid-August.
I asked about the Japanese maples, katsuras and dogwoods, and Buley thought they were all great but would need watering, especially during long dry spells. A trend she noted was the growing interest in the zone 5 peeling bark maple (Acer griseum), one of the toughest maples out there. In fall, it has dramatic red foliage; in winter, its red peeling bark is stunning; and during the rest of the year, its dark green trifoliate leaves are quite unique. Growing about 20 to 25 feet (six to 7.5 metres) tall, its spread can vary but is usually in the 15-foot (4.5-metre) range.
So many more varieties of shade trees are available. The trees mentioned here not only add great diversity to urban plantings, but also provide beautiful colour and pollinator opportunities. As this long dry summer has taken its toll on so many trees, the need for heat and drought tolerance has become far more apparent.
Any of these trees, planted in the right location, can offer tremendous cooling effects in summer, making our homes and offices more comfortable and helping us save energy on air conditioning. In addition to producing oxygen, absorbing pollutants, and providing bird habitats, the benefits of shade trees are many, especially in high-density areas. When the weather cools down this fall, consider planting at least one of these great trees around your home or housing complex.
Remember any new tree must be planted with great care and kept moist until well established so that it can thrive and delight you for years to come.