Winter Watch: Tree Health and Fungus Prevention in Calgary
Contributed by Jolene Ottosen for the Chaparral Green Thumbs
As Calgary settles into its deep freeze, winter is the perfect time to give your trees and shrubs a health check. While most fungal diseases slowdown in cold weather, winter planning, pruning, and cleanup can help prevent problems before spring growth begins. Although January is generally too early to start pruning, it is an ideal time to plan ahead. This is also a good opportunity to consider aesthetic and structural improvements that can enhance tree form and improve air circulation between branches. Regular pruning, done at the right time, encourages healthy new growth in spring.
Winter pruning is beneficial for many trees because they are dormant, making pruning less stressful and reducing the risk of spreading disease. With the leaves gone, it is also much easier to spot structural issues and lingering infections. However, do not prune trees or shrubs that bloom in early spring—wait until after they have finished flowering.
Tips for Winter Tree Care
• Inspect for damage and disease: Look for black knots, cankers, or resin on branches.
• Prune during dormancy: Late winter (February to March) is ideal for removing infected wood. Always cut well below the affected area and disinfect tools between cuts.
• Choose mild days: Prune only when temperatures are above freezing to reduce the risk of frost damage.
• Use proper cutting technique: Always use clean, sharp tools, and avoid cutting branches too close to the main trunk. Cutting at a node, where one branch connects to another, is preferable.
• Dispose properly: Bag and place infected branches in the trash—never compost them. Even professional compost facilities may not reach temperatures high enough to kill fungal spores.
• Plan ahead: If fungicide will be needed, note it now and apply it in early spring before bud break.
Below is a list of common tree fungi found in Calgary, along with their symptoms and treatment tips. If fungicide is recommended, check with a local arborist or garden centre to ensure you are using the correct product and applying it safely.
Final Tip: Healthy trees are more resistant to disease. Water deeply before the ground freezes, mulch roots (keeping mulch away from trunks), and avoid mechanical damage. If you are unsure about what you are seeing, take a photo and consult a local arborist or garden centre—they are always happy to help.
Stay warm, and happy winter gardening!
If you are interested in joining us in the garden next season, we would love to hear from you! Please email us at [email protected].
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