Tree and shrub care in your yard

Trees and shrubs help make Calgary the lush, environmentally vibrant place it is. Help protect our trees and shrubs with these maintenance tips.

Wait to water - if the ground is no longer frozen, and if tree buds are starting to swell, this is a good time to water trees. Established trees and shrubs (two years in the ground) do not require water as frequently as newly establishing plants. Most species will thrive on a good watering (to the root depth) one or two times a month during the growing season (April to September). You may need to increase this frequency to once a week during periods of hot weather. A good guideline for the amount of water is within the range of 38 litres per inch of trunk diameter when measured at 54-inches above grade.

Use a regular garden hose or a soaker hose and move the hose frequently to ensure that all the area under the tree's drip line is saturated. To determine the tree's drip line, look at where the rain falls from the tree during a rain shower.

Under the tree's canopy, loosen the soil to promote root growth and vigour. Grassy areas beyond the tree well can be aerated to allow increased water saturation, but be sure the aerator does not hit the tree's roots. Do not allow grass to encroach into the tree well.

Establishing trees and shrubs can also be fertilized once or twice a year. This should be done in early spring or fall using a slow-release, complete fertilizer containing moderate amounts of nitrogen (e.g. 22-14-14 or 20-20-20). It is not generally necessary to fertilize mature trees.

To prevent pests on your trees and shrubs, ensure that trees and shrubs have sufficient water and nutrients to maintain good health. Monitor plants regularly for pest activity and damage, which will occur together. Plant damage may take the form of spotty or discoloured leaves, leaf curl or roll, leaf perforations, or plant defoliation. Find out more about tree pests and diseases and how to fight them.

If small numbers of pests are present, early action can be taken in the form of pre-emptive tactics. Pests can sometimes be sprayed with water or handpicked Alternatively, a smaller tree or individual branches can be gently knocked with a stick or broom handle to dislodge pests. Place a sheet, tray, or garbage can lid under the tree to capture the pests and aid in dispatching. Also, yellow sticky traps hung from the tree's branches can be useful to keep pest numbers in check.

If pest numbers become excessive or reach infestation levels, population "knockdown" may be necessary. A mix of diatomaceous earth and water can be applied to plants to kill crawling insects. A horticultural oil mix may also be applied to plants to suffocate pests. Some plants do not tolerate this well so try this spray on a small portion of the plant and wait for a day or two to test for plant burns. An insecticidal soap, or permethrin mix, are other options for population knockdown. With all of these applications, be sure to follow label directions and apply the spray directly to the pests.

For more information, please visit our tree section or contact Parks.​​​​