Calgary Trees: What to plant!
Over the past 150 years, Calgary’s landscape has undergone a radical change from grasslands to urban forest. While many Calgarians grumble about how new infill projects are destroying the existing tree canopy in established communities and how new communities will never have a tree canopy because of small lots, big homes and underground services, in reality Calgary probably shouldn’t have any trees other than along the edges of the rivers (Bow and Elbow) and creeks (Fish, Confederation and Nose Hill) basins.
A view of the Bow River and Prince’s Island 100+ year ago. Note there were very few trees.
A view of Calgary today and how we have created an urban forest where there was once only grasslands.
The tree canopy of inner-city streets helps makes them more attractive places to walk. They also help to make the homes cooler in the summer.
Simply put Calgary is not a tree-friendly environment.
Calgary's tree canopy coverage (around 8.25%) is significantly lower than many other major Canadian cities, including Toronto, Vancouver, and Montreal, which boast 20-30% coverage. The city also has a lower canopy than other prairie cities like Edmonton (over 13%) and Winnipeg (17%). But there is a good reason for this.
Calgary has a harsher climate than other prairie cities because of our Chinooks. Chinook winds are bad for trees because the sudden warm temperatures can prematurely break dormancy, triggering sap flow and bud growth, which can then be killed by a subsequent cold snap. Chinooks also cause dehydration or "tip kill," where the warm, dry wind increases water loss from the plant while the roots are still frozen and unable to replenish it, leading to dried twigs and discolored needles.
Not only isn’t our climate tree-friendly, but the fact that Calgary’s airport and major water reservoirs are both within the city’s boundaries, means less trees.
But humans love to manipulate the places they live to create a sense of place that fits with their ideal aesthetics. In Calgary (and Canada for that matter) that means a front lawn with a big tree.
It isn’t just infill homes in established communities that have no place for trees, it is also in new communities where lots are smaller so duplexes and townhomes take up almost the entire lot, so there is no front yard so there will never be a tree canopy.
Even small older homes look bland without a tree in the front yard. Trees are great at hiding cookie cutter homes those built 75 years ago or today.
Who cares what these homes look like when you can’t see the homes for the trees.
Our trees are dying
Recently I had a chance conversation with Aaron Cull of Evergreen Ltd (B.Sc., Master Gardener, ISA Arborist and Certified Pesticide Applicator) about Calgary’s tree canopy. His biggest concern was the oystershell scale pandemic in our city. Oystershell scale first showed up in Calgary in May 2015, in cotoneaster hedges and has been spreading since then. It has the appearance of small clusters of oyster-shaped “shells” that adhere to the bark on shrubs and trees. It reproduces once per year and once hatched, the “Crawlers” feed on fluids found in the tree’s branches. They then permanently attach to the branch, developing a hardened shell that protects them from predators, the elements and most pest-control methods, while they ultimately kill the tree.
Trees planted on small spaces next to major roads like this one next to Crowchild Trail struggle to survive.
Plant less trees?
As Aaron I chatted I shared with him my view that perhaps Calgary should be planting less trees and more vegetation that is more suited to our climate and soil conditions. I know that idea won’t be popular with most Calgarians, so I asked him to share with me what are the best and worst trees to plant in Calgary. At least then, we won’t be wasting our time, water and energy on trees that don’t grow well here.
Best Coniferous Trees
Mountain Pine or Mugo Pine are great for our climate and they grow upwards not outwards. Bonus: They are drought resistant.
White and/or Blue Spruce are also drought resistant and have a conical growth shape that protects them from winds. FYI: Be sure to allow for a 30 foot area around the trees to all for full maturity spread.
Larches are great. Who knew Larch’s have heat stress genes that allow for tolerance in our arid climate.
Green Ash are structurally strong so they can withstand our winter storms and chinook winds.
Ohio Buckeye is the best for smaller areas by fences or garages.
Worst Trees to grow in Calgary
Columnar Aspens as the aggressive roots that can spread into lawns and foundations, disease prone and suspectable to damage in storms.
Chokecherry / Mayday as they to are easily damaged in storms and are very susceptible to black knot and oyster scale, and roots sucker around the base making it difficult to have flower beds underneath them.
Crab Apple (all species) as highly susceptible to diseases, dead branches and replacement withing 5 years.
Pear Trees and Hawthorne are very susceptible to Oyster scale.
Who knew American Elm are easily damaged due to their martini glass shape as they mature.
We have left the worst to last – cotoneaster hedges as they are the root cause of the spread of Oyster Scale.
Tree Growing Tips
The best time to plant trees is after the May long weekend when there is no more frost in the ground. This can stretch into the middle of June some years.
In the Fall, starting in mid-September, be sure to water your new trees once per week until middle of November to provide a protective coat of water around the root system. This will prevent frost cracks from occurring in the Spring during temperature fluctuations i.e. Chinooks, by allowing the tree to warm up from the inside out.
Mature trees and shrubs also need to be watered weekly after Thanksgiving to first hard frost to allow them to winter better.
Last Word
Calgarians love the tree lined streets of its inner-city neighbourhoods. In many communities you can’t see the house for the trees, which is often a good thing as the house design isn’t that great.
One of the reasons many people don’t like new communities is because of the lack of trees, to buffer the cookie cutter homes and new patina. Unfortunately, in new suburbs the townhomes and apartments will never have the grand trees to buffer their often cookie-cutter architecture due to underground utilities, front garages and small lots.
As I have said many times “don’t judge a community until the trees are taller than the houses.” Unfortunately, that isn’t going to happen with most new homes being built today.