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 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.

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. 

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. 

How do I deal with fireblight?

Prune diseased branches. The diseased wood must be disposed of at the landfill.

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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