While September and the fall may be around the corner, some Ontario residents have already noticed the leaves are changing colour. The red, yellow and orange burst of colour on deciduous trees like maple, oak and birch is usually the signal that fall is here and seeing it in August may seem a bit early for the leaves to start changing colour. It turns out, the wet weather is likely to blame.
“The trees that are changing colour early appear to be under stress,” University of Guelph Arboretum manager and certified arborist Alison Morrison said. “This year, heavy rains have been hard on urban trees with poor soil conditions and drainage. We seem to have heavy rain that moves quickly over the land and runs off without percolating through the soil to provide the tree with what it needs, or we have days of saturating rain that completely fills the soil and leaves the trees sitting in water.
” Neither condition is ideal, Morrison said. “Trees prefer a slow trickle that soaks in without oversaturating, leaving space for air and not drowning the very important soil fungi and bacteria that support a tree’s nutrient uptake.” Another issue adding to the stress on the trees this summer is the heat and humidity, which has created perfect conditions for fungal pathogens and some pests and diseases to breed in trees, Morrison said.
“Many species are suffering from various mildews, rusts, scales and wilts.” Healthy trees have robust immune systems that allow them to combat these infections by creating chemical or physical responses that slow the transmission. In years when they struggle to get enough water or air to their roots, it can be hard for them to mobilize these defences, and that’s when we see signs of stress.
Normally, the leaves’ colour change usually comes as sunlight decreases and cold weather moves in. “The changing colour is the chlorophyll in the leaves breaking down as the tree decides to go dormant to preserve the resources it has gained over the season for a potentially better future growing season.” The tree goes dormant to conserve energy.
“To be honest, there are still many unknowns about what triggers trees to start preparing for dormancy, but the agreement is that there are several factors, including lower light levels, temperatures and stresses,” Morrison said. “Additionally, some trees are just more sensitive than others, which could be due to their genetic makeup.” To see how your tree is coping, dig a little hole under your tree, Morrison said.
Is the soil too wet — is it dark and soaking? Does it small bad? That’s anaerobic bacteria from too much water, Morrison said. In this case, if the tree is large, there are not too many easy solutions, but looking at your tree’s roots for root flare can provide an answer. A tree buried too deep is already going to be oxygen deprived and so is less resilient when the soil gets saturated.
Root flare is where the tree’s trunk meets the roots and flares out. Ideally, you should see a portion of the root near the top of the soil. If you cannot find that root flare, try gently excavating around the trunk to understand how deep it is.
Then you can gently remove a layer of soil under the tree until you see fine root hairs and thicker buttressing roots just under the soil — that is your ideal planting depth. “This can be done in annual phases and the grade adjusted around your tree if the tree is much too deep,” Morrison said. “Any work you do should be gentle and in light phases, so the tree is not shocked by the changes you are making.
” Decomposed wood mulch is the best; it is full of beneficial fungus and bacteria that help break down nutrients so the roots can take them up, Morrison said. Make sure your mulch does not touch the trunk of your tree and the bark, Morrison said. “Pushing mulch against the trunk of your tree holds moisture against the bark, which can cause it to rot and effect the connection between the roots and the tree.
” When mulching, think of a doughnut, not a volcano. Also mulch lightly, too much can block oxygen exchange in the soil. An inch or two is plenty.
“We need this soil to dry out, get some air moving and get those roots growing.” Is the soil dry? Even large and established trees can receive help from a drink of water when the soil is dry. This means leaving your hose on trickle for an hour or so and moving it around under the branches of your tree.
“Do this once a week if there is not a significant rain fall that week, up until winter freeze-up. This should supplement your trees’ water needs and allow it to ease into dormancy.” If there is grass under your tree, raise your mower deck as high as you are comfortable with, Morrison said.
“Short grass uses lots of water and allows the sun to bake the earth. This warming of the soil evaporates water and kills beneficial microorganisms in the soil important to tree health.” Morrison even recommends removing sod under trees and applying a light layer of decomposed wood mulch to help cool the soil and keep the moisture in it for the tree to take up.
“Understanding the stress factors affecting our trees helps us appreciate the delicate balance they keep to survive and thrive. By recognizing these signs, we can better support our urban forests and ensure they continue to provide beauty and ecological benefits for years to come.” As fall creeps into the area, there are many opportunities to see the colourful leaves.
If you want to go for a drive, provincial parks will be full of colour in the next few weeks. At the moment, they are still not reporting any colour changing on the Fall Colour Report, which lets you know areas to view the colours at ..
