Fall is a critical period for trees as they prepare for the winter months ahead. As temperatures drop and daylight hours shorten, trees undergo physiological changes to prepare for colder weather. An adequate water supply during this time is crucial to support trees' metabolic activities and strengthen their defenses against winter stressors.
Deep watering plays a vital role in ensuring the well-being of trees throughout winter and into the beginning of the next spring. In Alberta, where the climate tends to be dry, September and October can bring a scarcity of moisture, causing many trees to suffer from water deficiency. Water scarcity during these months can be detrimental to tree health.
Benefits of Fall Watering
The significance of fall watering lies in its ability to help insulate the soil and, more importantly, protect tree roots. Cold conditions surrounding the root system can severely harm or even kill roots, resulting in branch dieback or, in severe cases, the eventual loss of the tree. Providing adequate water in the fall helps protect the soil and roots from harsh winter conditions.
Frozen water in the soil can help insulate the root zone and maintain soil temperatures warmer than the surrounding cold air. When roots lack water, they become more susceptible to damage from cold and dry conditions. Freezing and thawing can also cause damage to fine roots, putting significant stress on trees.
Well-watered trees are more resilient to winter stressors such as freezing temperatures, winds, and fluctuations in soil moisture. Proper hydration enables trees to endure these stressors and emerge in the spring with minimal damage.
It is important to note that newly planted trees are at a higher risk of sustaining injuries from winter cold compared to mature trees. Additionally, coniferous trees may lose water through their needles faster than their roots can absorb it during the winter months, resulting in brown needles during the spring, an occurrence known as winter browning.
To mitigate the risk of dead branches or the loss of entire trees, ensuring an ample water supply in the fall is crucial for tree survival during the winter months.
Root Health and Preservation
Root injuries resulting from cold conditions pose a significant threat to the vitality of trees and shrubs. In contrast to branches, buds, or trunks, roots do not enter dormancy simultaneously. Research indicates that roots continue their functions and growth during winter, especially when soil temperatures remain favorable. However, the physical effects of freezing, heaving, and soil cracking during winter can cause substantial harm to roots, particularly the delicate feeder roots in the upper layers of organic material.
Preserving the roots is of paramount importance:
- Thorough Watering: There is a common misconception that trees don't require water during winter. While trees use less water due to reduced transpiration (water loss through leaves) in winter, they still need hydration to endure the season. Ensuring adequate water before the onset of freezing temperatures is crucial. Deep watering for both young and mature trees is essential. Frozen water can help insulate the soil and minimize frost penetration into the root zone.
- Snowfall Advantages: Early snowfall is beneficial as it helps prevent the soil from freezing, even in severely cold air temperatures. Moreover, if snow arrives after the soil has already frozen, it acts as a protective layer, shielding the roots from temperature fluctuations during thawing periods in January or March.
- Mulch Magic: Mulching is a fundamental practice to shield roots. It inhibits weed growth, protects roots from extreme heat, and retains moisture. Creating a donut-shaped wood chip cover around your tree is a simple yet efficient approach to conserving moisture and minimizing soil freezing.
- Examine and Seal Cracks: For recently planted trees or trees growing in dry conditions, inspect the soil for cracks resulting from the planting process or dry fall conditions. Sealing these cracks can help prevent cold air from infiltrating the soil. Adequate mulching can also serve this purpose.
- Fertilization: On sandy soils, consider fertilization in the spring or fall. Conversely, for heavy clay soils, opt for fertilization after the leaves have fallen.
- Utilize Autumn Leaves: Rather than disposing of autumn leaves, allow them to remain on the ground, mulch them, or incorporate them into the soil. This practice aids in nutrient preservation. However, exercise caution if you identify leaf diseases (e.g., leaf spots, bronze leaf disease, etc.), as appropriate disposal may be necessary to prevent future complications.
Fall Watering Techniques
Proper fall watering involves more than simply adding water to the tree. Timing, how much and where you water, and maintaining adequate soil moisture all play an important role in preparing trees for winter.
Deep Watering: Ensure that the water reaches the root zone by watering deeply. Slow, thorough watering allows the moisture to penetrate into the soil and reach the root tips where it is needed most.
Timing: Timing the watering during fall can be challenging due to unpredictable weather in Alberta. However, understanding your local weather patterns is essential. For hardwood species, it is advisable to wait until leaves have fallen and just before the first soil freeze. The timing for coniferous trees is similar to that of hardwood species. Most trees enter a state of dormancy in the early weeks of October, just before the soil freezes.
Waiting until the ground is frozen will hinder water from seeping down into the root zones, as frozen soil acts as a barrier.
Preferably, water early in the day to allow plants ample time to absorb the water before nighttime temperatures drop.
Mulching: To complement watering efforts, mulching is highly beneficial, especially before the onset of freezing temperatures. Mulch serves as protection for tree roots against winter freezing, reducing the risk of root damage and tree mortality. Additionally, it aids in weed prevention, shields roots from extreme heat, and retains moisture around the trees. Creating a donut-shaped wood chip cover around your tree is an effective way to retain water. However, caution should be exercised to avoid placing wood chips next to the trunk, as this can attract rodents, insects, and potential diseases.
Applying a layer of 4-6 inches of wood mulch around the base of the tree helps retain soil moisture by reducing evaporation and preventing weed growth. This also moderates soil temperature, providing a more stable environment for root growth.
Where to Water: A common mistake is watering trees right next to the trunk. It is more effective to water along the "drip line," an imaginary line extending from the outermost branch tips straight down to the ground. Many of the tree's roots extend outward from the trunk, so watering around the drip line and beyond can help reach the root zone.
Amount of Water: Determining the appropriate amount of water involves a general rule of thumb: for every inch in the tree's diameter at breast height, approximately 10 gallons of water should be applied. Watering should be slow and deep, penetrating 6-12 inches into the soil.
Various methods, such as using a deep-root fork or needle (up to 8 inches into the soil), a soaker hose, or sprinklers, can achieve this. It is important to avoid spraying water on needles or foliage, and if sprinklers are used, water should not hit the tree trunk.
Monitoring and Adjusting: Regularly monitor soil moisture levels and adjust watering accordingly. Factors such as rainfall, temperature, and the tree's water needs should all be considered when determining the amount and frequency of watering.
Avoid Over-watering: While it is important to ensure adequate moisture, over-watering can be detrimental. Excessive water can lead to root rot and other issues. Pay attention to signs of over-watering, such as waterlogged soil or wilting despite sufficient moisture.
Water and Soil Sodium Analysis: Ensuring Tree Health
Prior to any watering activity, it is important to have a clear understanding of the sodium levels in both water and soil. Elevated sodium levels in water can pose a significant long-term threat to the health and survival of trees. Fortunately, various water and soil testing laboratories offer measurements of sodium levels, along with other essential parameters such as calcium, iron, magnesium, total dissolved solids (TDS), and electrical conductivity (EC).
The first step involves evaluating salinity and sodium levels in the soil. Soil salinity is quantified through the Electrical Conductivity of extract (ECe), measured in deciSiemens per meter (dS/m). Trees typically thrive in soil with an ECe of up to 4. Beyond this level, their growth becomes restricted. In soils registering an ECe between 8-16 dS/m, only saline-tolerant species may grow, and even their growth might be suboptimal.
The second step is to measure sodium levels in the water you intend to use. The addition of water with high sodium levels can progressively increase soil salinity over time. Most plants, including flowers, vegetables, and crops, do not perform well when water contains more than 100 ppm of sodium. High sodium levels can also gradually degrade soil structure, reducing water availability for trees.
Alberta Health guidelines recommend that chloride concentrations in drinking water remain below 250 mg/L (250 ppm). Trees exposed to excessive soil or water salts may exhibit stunted growth, reduced vitality, and, over time, could succumb to salt stress.
Conclusion
Fall tree watering is a crucial practice to support the physiological changes that trees undergo during this transitional season. Adequate hydration ensures that trees accumulate energy reserves, increase their defenses, and remain resilient to winter stressors. Implementing proper fall watering techniques, including deep watering, monitoring soil moisture, and applying mulch, contributes to the overall health and vitality of trees, ultimately enhancing their growth and appearance in the following spring.
Written by: Toso Bozic
Mulching is the most important activity that you can do to prevent root damage from winter freezing and reduce the possibility of root damage and tree mortality.
Use an irrigation bag for small tree watering with wood mulch to reduce the impact of cold air getting into the soil and damage roots (L and C); underground irrigation (R)