The Society receives many gardening questions. This page was created to share answers to some of the Frequently Asked Questions (FAQs).

Gardening Tips

Does leaving grass clippings on my lawn cause thatch?

Grass roots are the primary cause of thatch, not grass clippings. Thatch is made up of roots, stems, rhizomes and other plant materials. These materials contain large amounts of lignin (fibrous material) and decompose slowly. Grass clippings are about 80-85 per cent water with only small amounts of lignin, and break down rapidly.

To learn more about the practice of leaving clippings on the lawn, also know as grasscycling, read the information sheet from the City on the Society’s Resources page. The City also has lawn care information on their website

How can I attract beneficial insects to the garden?

Encourage biodiversity!  Choose a variety of plants that bloom throughout the season.  Plants of varying heights will attract different types of insects. Many beneficial insects prefer small, simple blooms.

How can I keep hanging baskets looking good all summer?

Soil in hanging baskets will dry out quickly, especially in windy conditions, so keep up with the watering – this is usually once per day and sometimes even more than that.  Make sure you match plant selections with their site.  Fertilize once every two weeks during the growing season with a water soluble fertilizer formulated for flowering plants.  Deadhead spent blooms when necessary.

What can I grow underneath a large conifer?

Large conifers will compete with other plants growing beneath them for sunlight, water, and space.   You need to be able to control these barriers to plant growth.  The simplest, most workable solution is to set up planter boxes/containers and then plant shade-loving species in them. (Watering will have to be done on a regular basis as the plants might not receive sufficient rainfall).  You are at least able to give the plants the soil and nutrition they require, without competition from the trees.

What are some herbaceous perennial selections for shady sites?

Hosta, bleeding heart (Lamprocapnos spectabilis), bugloss (Brunnera spp.), Ligularia, Astilbe, ferns, queen of the prairie (Filipendula rubra), among others. Visit the Perennial Plant of the Year page under Resources for more plant information. Society Members may visit the Society’s Plant Database under the Members Only section of the website.

How do I deal with fairy ring in my lawn?

If the rings are small, you can remove the top 5 cm of top soil and turf and reseed.   

How can I design my yard to conserve water?

Select water-wise native plants.  Grow less lawn.  Use mulch.  Make sure your soil is healthy. Use compost.  Install a rain barrel.  Water only when needed. Sign up for a Design Your Yard workshop to learn more.

Garden Diseases and Pests

How do I get rid of aphids? 

A strong blast of water from a garden hose is effective. It may be necessary to repeat the application. Using a soft, damp cloth to gently wipe sturdier plant leaves may work, as will handpicking. 

How do I prevent cutworm damage in the vegetable garden?

Keep the area around the vegetables absolutely weed free—this helps control the spread of cutworms because they like laying their eggs on plants that are not their food sources, such as grass. “Collar” your young plants as soon as they emerge out of the soil—you can raid your recycling bin and use empty toilet paper rolls or used single-serve yogurt cups (with the bottoms cut out).  Sink the collars about 2.5 to 5 cm into the soil.

How do I deal with powdery mildew? 

Be sure to water only at the base of the plants and do not splash water on the leaves.  Do not over water.  Poor air circulation can encourage the spread of powdery mildew as well—try to separate individual plants so that they are not crowded together and if you have a fan, run it gently near the plants to keep air going over the leaves.  If the plants are really dense, you may need to prune out some of the leaves (but not too many!) to open up the crowns so that more air will pass through.

How do I get rid of red lily beetles?

Although there are some biological controls under trial, the best way to remove the beetles is by handpicking and have them drop into a bucket of soapy water.  Look for adults, larvae, and frass in the soil and on all plant parts.  Diatomaceous earth may be applied to the soil and the leaves (make sure you cover the undersides of foliage, not just the tops). Bear in mind that red lily beetles will overwinter in the soil. They will eat all true lilies (not day lilies), Fritillaria, lily of the valley, and Solomon’s seal.

How do I manage slugs?

Warm wet weather results in a healthy population of slugs. Slugs are soft bodied creatures. Creating a coarse barrier between your plants and slugs can help control these pests, with diatomaceous earth being a good option. Please follow the safe handling instructions on the package of diatomaceous earth.

Hand picking slugs off leaves in the morning or evening can also be used for control. Placing a half grapefruit peel (dome up) in the garden is an attractive shelter for slugs. Check each morning, squish the slugs inside and reposition in the garden. Replace the grapefruit rind when required.

Keeping space between plants and removing decaying foliage will also help by make the environment less inviting to slugs.

How do I prevent vole damage? 

Make sure your lawn is mowed in the fall, just before the snow falls—tall grass provides a place for voles to hide.  You can purchase or make cylindrical guards from hardware cloth for your trees.  Sink the guards at least 5 cm into the soil, and make sure the cloth covers the tree well above what the average snow line would be.  Snap-type mouse traps baited with peanut butter may also work to catch them.

Is there any way to prevent dew worms from making a mess of the lawn?

Spread gypsum or coarse sand over the mounds.  The dew worms will not usually crawl over abrasive surfaces. 

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.

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. 

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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