How Does Weather Impact Our Trees?

Checking the weather forecast is a daily ritual for many of us. After all, weather impacts our physical and mental wellbeing. But weather also impacts other life forms including trees, which can be even more sensitive to its unstable nature. When the forecast calls for periods of undue weather, learn how to spot common stress symptoms in your tree so you can help protect it against potential threats before they become problematic.

Weather helps define the state of our atmosphere – think hot, cold, rainy, dry, etc. Like us, trees have their own preferred range of environmental conditions and when pushed outside their comfort zone by weather, they can become stressed. Frequent weather changes and prolonged periods of extreme weather (e.g., a heatwave) can create new or worsen existing stresses for a tree, as well as impact its ability to adapt to and resist potential threats (pests, diseases etc.). Here are some of the top stress-inducing weather events and how you can protect your tree against them.

Too much rain

An abundance of rain can oversaturate soil and reduce oxygen available for tree roots, leaving your tree with symptoms of wilting leaves, browning, leaf drop and even fungal diseases such as powdery mildew. So, when the forecast calls for extended periods of rain, be careful not over water your tree. Tip: always check the moisture levels in the soil around your tree before watering. To do this, stick your finger into the soil around the base of your tree – if it feels damp and cool, your tree should be good for another day and if it feels hard and dry, it’s time to water!

Powdery mildew on leaf(© Scott Nelson 2004_powdery mildew)

Fungal diseases spread in moist, warm conditions. Powdery mildew seen on this leaf could mean your tree’s environment is too wet. © 2004 Scott Nelson - powdery mildew

Extreme heat and drought conditions

Heatwaves pave the way for drought conditions and when trees lack water, many areas of their growth and development are impacted. Symptoms that show your tree is lacking water include early fall colour, leaf drop, browning along the leaf edges, and wilting leaves. To protect your tree during extended periods of heat, be sure to provide regular watering (approximately six gallons per tree, two to three times a week) and mulch, which will help retain water and protect roots.

Leaf with browning edges and discolouration(© 2016 Brenna Anstett / LEAF)

Browning edges of a leaf is a potential sign of drought stress. © 2016 Brenna Ansttt / LEAF

Extreme temperatures

Unexpected cold snaps or temperatures that flipflop between above and below freezing make trees vulnerable to cellular damage, especially in the bark, buds and leaves. Symptoms that show your tree is being impacted by low temperatures include cracked bark, blackened leaves, early leaf drop and reduced flower blooms in the spring. Protecting your tree from the effects of extreme temperatures starts at the pre-planting stage: increase resiliency by selecting a native tree that has evolved to the local climate.

Tree trunk with bark crack and trees damaged in winter ice storm(© 2013 Rosser 1954 (left) and © 2013 William F Hertha (right))

Left: The frost crack seen on this European beech tree is an example of a low temperature injury. © 2013 Rosser1954

Storms

High winds, heavy rain and ice buildup place a lot of stress on a tree, which can lead to fallen branches or structural damage. To protect your tree against storms, it is important to incorporate regular pruning into your tree’s maintenance. Pruning dead, dying and diseased branches can help reduce fallen branches during storms, while pruning to ensure structural integrity can better prepare your tree for the forces nature may inflict upon it over time.

The best way to prepare your tree for any type of weather is by minimizing pre-existing stress. Planting the right tree in the right place coupled with regular care, creates conditions for your tree to thrive and therefore better resist and adapt to weather as it changes.

Need help planting the right tree in the right place? The LEAF subsidized Backyard Tree Planting Program includes a consultation with a certified arborist who will assess your yard, recommend planting locations and native tree species that are best suited for your property’s unique soil, sunlight and spacing conditions. Apply online today to get started.

Jess Wilkin is the Residential Planting Programs Operations Supervisor.

LEAF offers a subsidized Backyard Tree Planting Program for private property. The program is supported by the City of Toronto, the Regional Municipality of York, the City of Markham, the Town of Newmarket, the Regional Municipality of Durham, the Town of Ajax, the Township of Brock, the Municipality of Clarington, the City of Oshawa, the City of Pickering, the Township of Scugog, the Town of Whitby, Ontario Power Generation, Ontario Trillium Foundation and Trees for Life.