During the spring, my most common question that comes into the office is, “Why is my tree turning brown?” The answer to that question begins with the most basic need for all living things, water. Water is essential for all plant processes. It aids in the movement of substances throughout the plant, serves as a medium for chemical reactions, and is necessary for photosynthesis.
Most of the water taken in by a plant is lost through transpiration. Transpiration is the loss of water through small openings in the leaf (needle) surface of the called stomates. Stomates also pull in carbon dioxide for photosynthesis. This transpiration creates a negative pressure which creates a pull or suction that draws water up through the stem and roots from the soil. Plants need to have a constant water source to minimize water stress like plant wilt. If water is not available, plant wilt can lead to decline and death of the plant.
Trees and shrubs have a deeper and more extensive root system than turfgrass, so they should be watered less frequently but for longer periods of time. It is always best to water just before you observe water stress, and there are a couple of simple methods that can help you determine when the best time is to water.
Soil moisture can be determined using a soil moisture probe, a screwdriver or long metal rod will also work. The probe will easily penetrate moist soil but stops when it reaches dry soil. The soil moisture in the root zone for trees and shrubs should reach 18-20 inches.
You can also use the feel method to determine the soil moisture. Squeeze a handful of soil to get an idea of the soil moisture level. The top four inches of the soil will dry out quickly, so take a soil sample four to eight inches deep to take a soil sample. This is where the roots should be absorbing water.
In sandy or loamy soils, if the soil remains in a ball without leaking water it is at a desirable moisture level, if it falls apart, or runs through your fingers, the soil is considered dry. In clay soils, if it is hard to break apart, it is dry, if you can make a ball and moisture and stain is left on your hand, it is adequate for moisture.
Trees and shrubs should be watered to 18-20 inches. Soil type determines how quickly water is absorbed into the soil. Sandy soils absorb water fastest with an average of two inches per hour, loamy soils absorb water at a quarter of an inch per hour, and clay soils absorb water at half an inch per hour. By allowing water to penetrate deeper into the soil you are encouraging deeper rooting and a more drought tolerant tree.
This time of year, it is vital to protect your trees from damage done during the winter. Trees will continue to transpire during the winter, especially evergreens. Deep watering your trees in the fall will protect them and give them the water they will need throughout the winter.
Water throughout the root zone of your trees, the root zone typically is wider than the canopy of the tree. If I have a tree reaching out 10 feet from the trunk, the root zone may reach 12 feet in distance. Trees planted near sidewalks, roads, and parking lots have an added pressure of not being able to get water from part of their root zone.
If watering with a sprinkler system, water the zones around trees and shrubs for longer periods of time. The easiest way to ensure adequate water for trees and shrubs is to lay a garden hose at the base of the tree or along the drip line and let it run slowly for at least four hours. Move the hose around to ensure all the roots receive water.
To aid watering on sloping sites, consider drilling three or four holes approximately 18 inches deep and two to three inches in diameter at an angle pointing outward from near the base of the tree. Insert a perforated plastic pipe and fill it with medium sized gravel. Fill each pipe with water several times, or until water does not penetrate the soil anymore. This will ensure that the water you put on the ground will penetrate at least 12 inches for good root zone moisture content.
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