In the vast landscape of the tree and seedling industry, certain trees raise eyebrows and elicit pointed remarks from customers. At TreeTime.ca we believe that no tree or plant is inherently ‘bad’. It is all about planting the right tree, in the right place. With certain species requiring additional thought and selective planting.

In this Gardening at USask video, Drew covers a few different varieties that require further consideration as well as the importance of making informed choices when it comes to planting. 

Caragana: A Misunderstood Tool

  • Common Caragana is a controversial shrub that is often criticized for its invasive nature.
  • However, it can serve as a valuable tool, especially in challenging environments like dry areas with limited soil moisture. Without a row of Caragana, establishing a shelterbelt can be very difficult.
    • Planting a row of Caragana helps trap blowing snow and accumulate leaf litter, which increases soil moisture. This, combined with added wind protection allows the subsequent rows in the shelterbelt to establish.
  • We are not suggesting that Caragana be planted everywhere, for every project. The key is to plant caragana selectively, understanding its purpose and not planting it indiscriminately.
  • Alternatives: Lilac, Willow, Sea Buckthorn, Red Osier Dogwood, Silver Buffaloberry, Saskatoons, Siberian Crab Apples.

Siberian Elm: Proceed with Caution

  • The Siberian Elm seeds prolifically. The seeds have the potential to be transferred throughout waterways. This can cause it to become invasive, especially in warmer climates.
  • This, in combination with its relatively short lifespan, does not make it an ideal tree for many projects. We no longer advocate its regular use, urging customers to explore better alternatives suitable for their specific regions.
  • Alternatives:
  • Dutch Elm Disease:
    • To help prevent the spread of Dutch Elm disease, it is important to prune your trees at the correct time of year. Avoid pruning trees when elm beetles are the most active. Many provinces have pruning bans in place for Elm Trees.
      • Alberta: April 1st – September 30th
      • Saskatchewan: April 1st – August 31st
      • Manitoba: April 1st – July 31st
    • Properly dispose of Elm wood at the landfill.
    • Do not store, use, or transport Elm wood.
    • Report suspected Dutch Elm Disease to provincial authorities.

Plant the right tree, in the right place

Peking Cotoneaster: Hedging your Bets

  • The Peking Cotoneaster is a popular hedge species that is found in many urban yards.
  • Once lodged in tight spaces, it persists, making removal of the root system very difficult. It can easily become invasive. 
  • The key takeaway here is to plant with care, considering the potential challenges associated with its resilience.

Tower Poplar & Swedish Aspen: Root Runaway

  • Tower Poplar have an Invasive root system that produces aggressive suckers. It is a tree that is suitable for lake lots and colder climates, but in warmer climates, it can take over. 
  • If you are in a warmer climate and looking for a columnar variety, the Swedish Aspen is a better alternative. It does not sucker as readily, limiting its spread. 
  • However, the Swedish Aspen does come with other considerations. It is more susceptible to Bronze Leaf Disease, especially with many trees planted close together.
  • Aspens & Poplars have a shallow root system which can potentially cause sidewalks to crack and heave. Tree roots are capable of taking advantage of structural weak spots. So if you have a sidewalk or driveway that already has cracks throughout, tree roots will often find the path of least resistance and exploit these gaps or cracks.

Russian Olive: Responsibly Beautiful

  • Russian Olive, is considered a beautiful ornamental tree as well as a controversial one. In Edmonton, Alberta they are often planted as a boulevard tree. Whereas a few hours south, in Calgary, Alberta, they are considered invasive.  
  • In warmer climates and along waterways the seeds are easily dispersed. They can become impregnated along a waterway and can take over a watershed. There are many areas within the United States that have spent hundreds of millions of dollars to remove Russian Olive from watersheds. We do not want that kind of problem here in Canada.
  • Responsible use is important, avoid planting along waterways and in warmer climates. If you do plant the Russian Olive, find ways to reduce the release of seeds. 

Chokecherry and Other Prunus Varieties: Tackling Black Knot

  • Chokecherry, as well as others in the Prunus genus (Cherry, Plums, Peaches), face the challenge of Black Knot . 
  • Black Knot is caused by the fungus Apiosporina morbosa, which causes black, tar-like swellings on the branches. It is a manageable issue with proper maintenance. 
  • Black Knot best practices:
    • Prune infected branches when the plant is in dormancy. This would be in the late fall, winter, or very early spring.
    • Prune branches at least 15-20cm (6-8”) below the knot, or remove the branch entirely.
    • The infected branches have to be disposed of correctly by either burning or burying. This helps to prevent the spores from spreading and infecting a neighboring tree.
    • Disinfect pruning shears before and after pruning. 
  • Black Knot can easily start to spread throughout an area or neighborhood. Be a responsible neighbor by preventing the spread of diseases and maintaining a healthy tree population within the community.

Sea Buckthorn: Thriving with Attention

  • Sea Buckthorn is capable of growing in a wide range of soil types, including dry, saline, and alkaline. It is both resilient and fruit producing making it well suited for a variety of projects. 
  • We have heard claims of its invasiveness due to suckering and birds spreading the seed. But it does not seem to be a widespread issue or concern. 
  • It emphasizes the need for hands-on ownership and regular maintenance to prevent unwarranted spreading.

Green Ash: A Favorite Under Threat

  • Green Ash is a beloved and widely planted tree due to the great canopy cover. It is frequently planted as a boulevard tree in many cities, including Edmonton, Alberta. 
  • It faces a looming threat from the emerald ash borer, which has been spotted in southern Manitoba. With about 30 to 40 percent of boulevard trees in Edmonton being Green Ash, there’s a collective responsibility to protect this tree species from potential devastation.

As stewards of the land, it is important to plant the right tree, in the right place. Selecting trees wisely is a shared responsibility, involving consideration of both the land and climate, along with specific project and maintenance requirements. Remember, we are all part of the solution.