Preparing Trees for Winter by Toso Bozic

As fall officially starts in 8 days, September 21st, Toso Bozic of the ATTS Group has put together some fact sheets about helping trees through the fall and winter months.

1. Fall is very dry and watering trees is crucial for root survival and health, see this video for how soil drought can affect watering.
2. Soil dryness creates cracks that cold air can enter during winter and kill the trees. Tree death in winter is very common and soil dryness is one of the main causes of tree mortality.
3. Wood chips are you're best friend for protecting roots
4. Rake and remove tree leaves if you know they are infested by Bronze Leave Disease, Melanspora Leaf Rust or any other diseases, otherwise keep these leaves as mulch.
5. You should only prune dead and broken branches and should not prune in fall, especially fruit trees.

As trees are preparing for winter, deep watering may help their well-being during the cold winter months as well as at the beginning of next spring. The majority of Alberta is dry with very little moisture during September and October, with many trees experiencing water deficiency during these months. The main reason for watering in fall, prior to winter, is that water acts as an insulator to the soil and most importantly to the roots of trees. Cold air around the root system will greatly damage or kill roots, causing branch dieback or eventually kill the tree.

Having frozen water in the soil makes it warmer than the surrounding cold air. Roots without water around them will be more susceptible to cold dry air damage. Cold air in the soil will draw water from roots and create icicles in the live root cells. Icicles in root cells damage or kill fine roots causing significant stress to trees. Newly planted trees are more prone to winter kill injuries than mature trees. Be aware that during the winter months the coniferous trees may lose water through their needles faster than their roots can absorb it, which will turn needles brown in spring. This process is called winter browning.

To avoid dead branches or entire trees being killed, providing sufficient water supply in the fall is crucial for tree survival during harsh winter months.

Image 1: Epicormic  shoots and top branches dead due to winter root damage on old and young elm trees

Water and Soil Testing for Sodium

Prior you do any watering you should make yourself aware of the sodium levels in water and soil. If you have a high sodium level in water, you are setting up your trees to be killed in the long run. Any water and soil-testing laboratory can measure sodium levels in water and soil. Most labs will measure Calcium, Iron, Magnesium, and many others including Total Dissolved Solid (TDS) or Electrical Conductivity (EC)

The first step is measuring the salinity/sodium levels in the soil. Salinity in soil is measured as Electrical Conductivity of extract (ECe) in deciSiemens per meter (dS/m). Most trees will grow in soils with an ECe of up to 4, but beyond that level their growth is restricted. With a soil with an ECe between 8-16 dS/m, only saline tolerant species may grow, and their growth may be only satisfactory.

The second step is to measure the sodium level in the water. As you add water with high sodium levels, you will increase the overall salinity in soil year after year. Most plants (flowers, vegetable, and crops) do not perform well when more than 100 ppm of sodium in water.

According to Alberta Health most of the Chloride concentration for drinking water is less than 250 mg/L or 250 ppm.

Trees affected by salt will have a stunted appearance and reduced growth and many will succumb due to higher doze of salt in soil or on trees itself.

Timing

When to water in the fall is hard to determine, as the weather in Alberta is unpredictable, but you should know your local weather situation and act accordingly. For hardwood species, you should wait until leaves fall off and just prior to first soil freezing. For coniferous timing, it is the same as for hardwood species. Most of the trees will 'shut down' in the early weeks of October just prior to soil freeze. If you wait and the ground freezes, frozen soil will act as barriers and water will not seep down to the soil to the root zones. Always water early in the day, so the plants have time to absorb it before the temperature drops at night.

Where to Water

Most people make the common mistake and water trees right next to the trunk. Trees should be watered at what an arborist calls the 'drip line' –an imaginary line extending from the outermost branch tips straight down to the ground. Most of the roots are spread beyond the drip line and usually are equal to the tree's height.

How much to Water

As a rule of thumb for every inch in the tree's breast height diameter, equals 10 gallons of water. Watering should be slow and deep (6-12 inches). There are several ways to water trees by using a deep-root fork or needle (up to 8 inches into the soil), using a soaker hose, or sprinklers. Avoid water spraying on needles or foliage. If you use sprinklers avoid water hitting the tree trunk directly.

Image 2: Use an irrigation bag for small tree watering and wood mulch to the reduce the impact of cold air getting into the soil and damaging roots.

Mulching

Beside watering you may also add the mulch to your trees before freezing. Mulch protects tree roots from winter freezing and reduces the possibility of root damage and tree mortality. Mulching also provides several other functions, such as preventing weeds, protecting roots from extreme heat and keeping moisture longer around trees. Create a donut-shaped wood chip cover around your tree to keep water inside. Putting wood chips next to the trunk attracts rodents, insects, and potential diseases.

Harsh winter climates in Alberta can create many damages to trees and shrubs. Some of the most common damages occur due to cold temperature and dry air, winter sun, wildlife damage, salt, deep freeze, heavy snow and ice. There are a few things you can do to reduce potential damages.

Cold Winter Damage and Prevention

Cold winter damage can happen due to a tree's inability to survive cold weather, lack of snow in some parts of Alberta, strong cold and dry wind and heavy snow and ice in late fall or early spring. There are few things you are able to do to avoid cold winter damage:

• Choose hardy trees and shrubs that can withstand cold temperature. Alberta belongs to Canada Cold hardiness zones 1, 2 and 3 and partly zone 4. So choosing trees and shrubs that are hardy enough for our climate is the first step to protect them from cold weather
• Snow is an excellent insulator for trees and shrubs
• Plant trees and shrubs in protected area buildings (or already established tree shelter) to avoid direct exposure to strong wind
• Proper pruning will reduce the number of branch breaks during heavy snow or ice

Root Injuries and Protection

Root injuries due to cold are one of the most impactful damages that trees and shrubs can sustain. Roots do not become dormant at the same time as branches, buds or trunks/stems. Several studies are showing that roots remain mostly inactive. Roots can and do function and grow during winter months, whenever soil temperatures are favorable, even if the air above ground is brutally cold. The freezing, heaving and cracking of winter soil physically damages roots, particularly the fine feeder roots in the uppermost organic layers. The root damage can also trigger a range of effects, such as reducing a tree’s ability to take up water and nutrients, particularly during a spring bud break, and to support stem and branch growth in summer. Severe root damages from winter will greatly contribute to whole, or partial, tree mortality.

To protect roots is the most important thing that you can do for trees and shrubs. Here are several recommendations:

• Provide deep watering just before freeze (young and old trees). Frozen water is an excellent insulator and will reduce frost penetration to the root zone. Moist soil holds more energy than dry soil. Once the soil is dry, it is easier for the frost to penetrate deep and dry out roots. The freeze will take moisture from roots and create crystal icicles in the roots which will create physical damages to the root system. The best way to water is slowly, with a soaker hose, at an approximate rate of 10 gallons (around 40 liters) per inch of tree diameter (tree diameter is measured at breast height).
• Good deep early snowfall will keep soil from freezing even if the air temperature is brutally cold
• If snowfall happens after the soil is already frozen, deep snow will protect the roots from January or March early thaws, when the temperature fluctuates
• Mulching is the most important root protection you can do. Mulching provides a few key functions, preventing weeds, protecting roots from extreme heat and keeping moisture around trees. 
• For newly planted trees check if there are cracks in the soil due to planting or a dry fall. Fill in these cracks with soil to prevent cold air from entering. 
• For sandy soil you should fertilize in the spring and for heavy clay soil you should fertilize in the fall.
• Instead of disposing of fall leaves, keep leaves on the ground, mulch or blend them into the soil to retain nutrients. Be aware of leave diseases and rake to avoid problems.

Wildlife Damage and Prevention

As winter is very harsh for many wildlife species, they are looking for food usually on young and recently planted trees. Several wildlife species can create damage to your young trees. Mice, voles, rabbits, deer and moose will griddle and eat the bark, twigs, branches and buds by feeding on them. They can create severe damage, including total or partial destruction of trees and shrubs. There are a few things you can do, such as erecting physical barriers, to prevent damages:

• Use mesh wire (1/4 inch in size) to protect trunk bark from mice, rabbits, voles and to some extent deer and moose. Deer and moose will strip bark either by eating or using their antlers.
• Use plastic tree guards for small animals.
• Properly install mesh wires or plastic tree guards with no gaps between the bottom of the mesh cylinder and the ground where animals could crawl under the fencing.
• Build a large fence for deer or moose and use repellant.

Image 3: Meshed wire and plastic guards around tree trunks.

Salt Damage and Prevention

Various salt (chlorides) are used to prevent ice from forming on the road in Alberta. Some studies show, sodium chloride is one of the most damaging agents on trees and shrubs. There are several things you may able to do:

• Avoid or reduce the amount of salt used for de-icing
• Plant salt-tolerant trees and shrubs in areas with high use of salt
• Use other alternative de-icing material such as sand or small gravel
• Put some trees under burlap to prevent salty spraying particles on the trees
• Move trees and shrubs further away to avoid salt damage

Image 4: Burlap to protect trees from salt around the driveway. Street trees are buried in snowpack with heavy salt in it.

Pruning

After leaves drop, in September and October, you may be considering prune dead, diseased and damaged (3D) branches. Dispose of or burn any infested branches. Perform proper 3-way cut pruning techniques and do not damage the branch collar during this process. Otherwise, avoid pruning at this time of year as this may create additional stress to the tree.

Image 5: A broken branch that needs to be removed and proper pruning, allowing the tree to heal a wound.

For more information:
Toso Bozic P.Ag
ISA Certified Arborist
CERT ID: PR 5356A
(780) 712-3699
bozict@telus.net
www.yardwhispers.ca or www.attsgroup.ca