Did you know that the sudden appearance of brown foliage on evergreen trees and shrubs that we see in March and April is often a result of winter desiccation? Every spring we get calls from property owners wondering why their cedars, spruces, yews, junipers and boxwoods are suddenly showing signs of browning foliage in March and April. Here is a brief explanation of the problem, and some practical ways to prevent your evergreens from desiccating this winter.
Evergreens are plants that retain living and functional foliage all through the year, often remaining functional for multiple years. Although evergreen foliage is resilient to our winter conditions, this foliage can be vulnerable to desiccation during mild spells where we experience sunny conditions such as during a typical “January thaw”. This vulnerability to winter desiccation exists because evergreens rely heavily on stored water reserves in the root system to carry them through winter dormancy.
Susceptibility to foliar water loss in winter is even greater if the evergreens have been planted in the last few years or if excavation has occurred within the root zone. Newly planted trees have a very limited root system, and it can take as much as 3-5 years for them to create a balanced root system that can fully support shoot growth. Trees that have suffered root loss due to construction activity in the tree protection zone of the root zone can be especially vulnerable to winter desiccation due inadequate water storage in their remaining root system.
Evergreens (like this low growing groundcover juniper) located near cement and stone walkways are more susceptible to winter desiccation since the hardscape surface reflects sun and heat onto vulnerable evergreen foliage during mild, sunny winter weather.
To further understand winter desiccation, let’s go back to our high school biology for a moment. You might remember that plants make their own food through a process known as photosynthesis – opening their leaf pores to capture atmospheric CO2 and using light energy to convert the CO2 and available water to sugar (plant food). These plant sugars are stored in leaves, stems and roots to be called on later when needed. Evergreen foliage is therefore a significant storehouse for sugars and water, making evergreens extremely vulnerable to events that result in foliar loss. This is why spruce trees are often unable to recover from a single, significant defoliation event (>50%) such as those that resulted from Spongy moth infestations in 2021.
Since evergreens retain their foliage all year round, unusually mild and sunny afternoon conditions in winter can signal the opening of their leaf pores. Yes, even in winter! Instead of an opportunity for sugar production, the low light levels in winter are inadequate to provide enough light energy for photosynthesis and the leaves just end up losing precious stored water. This water loss causes evergreen leaf tissues to dry out (desiccate) and then die and turn brown. This is why we see the signs of winter desiccation mainly on the southwest side of the tree – the afternoon sun side. In the southern Ontario landscape, it is easy to find this type of injury on young evergreen trees, shrubs and groundcovers that have afternoon sun exposure.
Thankfully, it is just the leaves that are killed but remember that those leaves hold major storage reserves of plant sugars and water. For evergreens that lose more than 25% of their foliage, it can be very difficult for them to regrow fast enough to replace the sugar and water stores that were lost. Without their foliar storage reserves, plants become stressed and can be more susceptible to environmental issues, pests or mechanical damage.
Where winter desiccation damage is minor, stems and buds for spring growth remain alive and will eventually regrow to screen the areas where evergreen foliage has been killed. Unsightly desiccated twigs can be pruned out, leaving more desirable foliage and space for nearby twigs to grow into.
The good news is winter desiccation is largely preventable. At Beautiful Trees Inc., we can protect your vulnerable evergreens with our Anti-Desiccant Treatment. Anti-Desiccant Treatment is applied just prior to the onset of winter to provide a protective coating on evergreen foliage that helps to seal in precious water. Anti-Desiccant Treatments will naturally weather or wear off over the winter months, leaving foliage healthy and ready to grow by the following spring. Contact us for a Free Quote to have your beautiful evergreen trees protected in November and early December.
Another prevention option is to construct burlap barriers around your evergreens. These physical barriers can block the sun’s energy and help keep evergreen foliage dormant. In areas where de-icing salts are used near evergreens, it is important that the burlap barrier does not directly contact the evergreen foliage. De-icing salts tend to accumulate on burlap barriers and can easily leach through and onto vulnerable evergreen foliage.
Call us today to book your free on-site estimate to protect and inspect your beautiful trees and shrubs this fall.
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Bolton, ON
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Beautiful Trees Inc.
Main Office (Johl Anderson)
206 Hickman St
Bolton, Ontario L7E 2P4
(416) 738 – 4137
Thornton Yard ( Jon Fry)
5089 20th Sideroad
Thornton, Ontario L0L 2N0
Vandorf Yard (Chris Ward)
2375 Vandorf Rd
Stouffville, Ontario L4A 2J7
Monday – Friday 9 AM to 5 PM
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