Using Marginally Hardy Trees in the Landscape
I just got back from Montana, and was somewhat surprised with how much more variety they are able to use with trees and shrubs, only a few hours south of us. Oaks and maples, that barely make it through winter in Alberta, make majestic street trees in towns like Bozeman, Missoula, or Livingston.
Unfortunately, our choices for street trees are limited in Alberta, and many of our staples face ever increasing threats from invasive insect pests, such as European elm scale, oystershell scale, and inevitably, Emerald Ash Borer and Dutch Elm Disease, both lingering just east of the province as of this writing (Sept 2018). Whenever I meet a fellow arborist, be they municipal or residential in specialization, we drift to the same topic of, “What are we going to use for street tree options?” But that’s the subject of another article.
So the same tree that grows to a height of 40′ or more in Montana, might make it through the winter here, and put on one to a few inches of growth per year, maxing out at a much shorter height and width. But so long as it’s hardy (ie. makes it through the winter intact), it can be a useful accent in our ornamental landscapes, or a welcome addition to our short list of small trees.
In the picture above, I used a serviceberry (basically a single-stem Saskatoon tree) as an accent in a bed of mature daylilies and irises, planted close to both my house and my neighbour’s. And even though this tree is sitting in 24″ of black dirt, and gets all the loving care it needs, it barely puts on new growth, maybe 1/4″ per year. But it flowers nicely, leafs out, bears fruit, and has excellent fall colour. What do I care if it grows? It’s perfect as it is.
In the above pic, I used a norther pin oak as a small tree to add height and contrast next to a heavily trained ‘Royalty’ crab and some dwarf hybrid lilacs. The slight nitrogen deficiency in the oak creates a lovely chartreuse colour that contrasts nicely against the deep purple leaf of the crab. The oak is growing at such a slow rate, I can keep this look and balance for many years.
My suggestion for people who want to create a bit of new interest in their tree and shrubs beds is to experiment with some new marginal trees (avoid zone 4, however, unless you like wasting money). So long as the tree makes it through winter, it is hardy. Worst case scenario is that you rip it out and try something else. For the hard-core gardeners, this can prove to be quite a bit of fun.
(c) 2018 Shane LePage, Wild Rose Garden & Tree Service Inc., Red Deer, AB.