Different trees have different water requirements, but as a general rule, most trees need about 10 gallons of water every week or two, for every inch of tree diameter at breast height (about 4.5 feet above the ground). In other words, a walnut tree with a 6-inch-diameter trunk will require about 60 gallons of water every other week.
There are a number of factors that influence a tree’s water needs, including those detailed below. Be sure to consider these factors carefully when deciding upon a supplemental water regimen for your trees.
The Tree Species
Some tree species simply need more water than others do. For example, a black cherry tree usually requires more water than a redbud does. Typically, a tree’s water needs reflect the habitat from which they hailed, although there are a few exceptions.
The Geography and Surrounding Habitat
Trees growing in hot, windy and exposed locations will require more supplemental water than those growing in damp, sheltered locations. Additionally, trees growing lower in a water shed usually require much less water than those growing on hills or high slopes.
The Age of the Tree
Older trees, who have more extensive root systems, generally require less water (relative to their size) than younger trees, as they are able to withdraw more water from the soil. Many large, mature trees only require supplemental water during extended droughts.
The Health of a Tree
Trees that are battling pests or pathogens may have different water requirements than those who are in good health. Additionally, those trees that have become stressed by drought or poor weather may require more water than trees that have not been exposed to such conditions.
The History of the Tree
The things a tree has experienced over the course of its life may alter its supplemental water needs. For example, trees usually require significant quantities of water for the first year or two following installation.
Methods of Administering Supplemental Water
You can apply water to a tree’s root system in a number of different ways. Some of the most common strategies include the following:
Simply spraying water on a tree’s roots with a hose is a viable method for those with the time to do so (it takes about 5 minutes for a medium-pressure hose to dispense 10 gallons of water). Be sure to apply the water around the dripline, where the bulk of the absorbing roots are, rather than saturating the soil near the trunk.
Sprinklers are not an ideal method by which to supply trees with supplemental water, but they will work if need be. Just be sure to aim the sprinklers so that they are soaking the ground near the drip line, and that they aren’t repeatedly spraying the trunk.
Unlike traditional sprinklers, which waste a lot of water, drip irrigation systems use tiny spray heads to deliver the water right to the soil. Drip systems are ideal for those with small groups of trees, although they can be designed to cross long distances if necessary.
Like drip irrigation systems, soaker hoses are a very efficient way of watering trees, and because they allow you to provide a lot of water over a long period of time, they are ideally suited for watering trees.
If you need help determining the water needs of a tree on your property, reach out to your friends at Evergreen Arborist Consultants. One of our experienced tree-care professionals will visit the property, inspect the trees in question and help you arrive at a reasonable estimate of its water requirements.