The Society receives many gardening questions. This page was created to share answers to some of the Frequently Asked Questions (FAQs). If you don’t see your question listed here, check out the options on the Gardening FAQs page.

Tree and Shrubs Tips

What do I do if the leader of my conifer has broken?

A leader is the tree’s main upright stem. If it breaks, the tree will push the growth of the lateral branches surrounding the site of the original leader, to create a new leader. To support a new leader, prune back the competing growth so the tree once again has a clear, single leader. For all trees, having a healthy, strong leader is important to the structural integrity of the tree. 

What are some columnar or narrow tree selections for small spaces?

‘Rosthern’ columnar crabapple, ‘Gladiator’ flowering crabapple, ‘Prairie Spire’ green ash, ‘Moonglow’ upright juniper, pyramidal mountain ash, and ‘Parkland Pillar’ birch, among others.   

Do poplar/aspen trees break foundations of buildings? 

Poplars and aspens have thirsty roots and will actively seek out water sources. If there is an existing crack or leak in a piping/plumbing system or a source of water in the foundation, they may grow towards it. If the area is dry, there should not be a problem. When planting any tree, always allow sufficient space for roots to grow—do not plant large trees too close to buildings or other structures.

When can I prune my lilac?

The best time to prune a lilac bush is in early summer, right after the current flowers have faded. This prevents accidentally cutting off the buds for next years flowers, which start forming soon afterwards on this year’s wood.  Without pruning, lilacs will eventually flower only on the upper tips. Pruning encourages new growth and promotes more blooms all over the shrub.

What are the recommended trees for Calgary?

The City of Calgary has a page dedicated to the top trees species for Calgary. Use this link to visit the page for more information about the trees.

How do you plant a tree?

Choosing the correct tree to plant and planting it in a suitable spot often requires careful decision. To find out more, read the How To Plant a Tree leaflet.

Tree Diseases and Pests

How do I deal with black knot? 

Prune away infected branches 5 to 10 cm below the individual knots. Dispose of the diseased branches in the landfill. Prune when the trees are dormant. To find out more, read the Black Knot in Trees leaflet.

What is Cytospora Canker?

Cytospora canker is a fungal disease that attacks trees that are injured, weak or stress. It can occur in deciduous or coniferous trees. To learn more, read the Cytospora Canker in Trees leaflet.

How can I treat poplar trees for bronze leaf disease?

Prune out infected branches.  Pick up all leaf litter from infected trees.  Dispose of diseased branches and leaves in the the garbage. Do not compost them.  If the problem is severe, consult with a certified arborist. Read the Bronze Leaf Disease in Trees leaflet for more information.

How do I deal with fireblight?

Prune diseased branches. The diseased wood must be disposed of at the landfill. To learn more, read the Fireblight in Trees leaflet.

What is European Elm Scale?

European Elm Scale is a pest that often attacks elm trees by penetrating the tree bark and leaves and sucking the juices. The pest eggs hatch in June and feed on the leaves in July. For more information, read the European Elm Scale in Trees leaflet.

How do I deal with Oystershell Scale?

Oystershell Scale is an invasive species that attaches to tree bark and causes injury. Regular watering, pruning and ensuring that your tree and shrubs are in a biodiverse enviornment may help prevent Oystershell Scale. To find out more, read the Oystershell Scale in Trees leaflet.

How do I identify and deal with leaf rollers in my aspen and poplar trees? 

The leaves of the trees will be rolled up and often will contain a small white worm within.  Fortunately, leaf rollers only have one generation per growing season, so they will move on quickly—there is no need to take action. Keep the trees as stress-free as possible.  Maintain a regular watering schedule, feed them in the spring with a side dressing of compost, and mulch them for winter protection. 

How can I control spruce sawfly?

Handpicking or spraying the larvae with blasts of water from the garden hose to knock them off may work just after they have hatched.  (They usually feed on lower branches first).  If the infestation is too severe, a consultation with a certified arbourist may be necessary. 

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