There are right ways to water trees, and wrong ways.
Watering a tree the wrong way can make it susceptible to fungal disease, such as crown rot, and water-stress. While roots are meant to be exposed to soil and water, bark is not.
The two most common wrong ways include planting a tree in the center of a bowl-shaped depression, where water pools around the trunk, or using a sprinkler that sprays the trunk. In both cases, water ends up collecting in the crevices of the bark, causing rot and fungal infection. Improper planting depth and over watering are the two most common causes of tree death.
While you can certainly water your trees with a hose, irrigation rings can save time and provide the water more slowly, preventing runoff. Irrigation rings are handy tools for preventing shade tree decline and conserving water.
Where do trees need water?
If you’ve ever stood under a tree canopy when it’s raining, you know that most, but not all, rain water is deflected away from the trunk by the leaves. The leaves farthest from the trunk form what is know as the tree’s drip line.
Trees have evolved in ways that protect the trunk from excessive moisture, while allowing rain water to reach tree roots. Roots that grow beyond the canopy absorb the lion’s share of rainwater. You can mimic this action by providing irrigation water in a ring at the drip line of mature trees.
Types of irrigation rings
Irrigation rings provide water where it is needed most, in the top 2 or 3 feet of soil, by releasing the water slowly. Irrigation rings come in many forms:
Or, you can do what I do, which is simply to dig a shallow trench, 4” deep and wide, in a circle under or slightly outside of the drip line. If you have a semi-dwarf tree with a canopy that is 8’ across, and a trench 4” wide and deep, that trench will hold approximately 20 gallons of water. One added benefit of the trench method is that it helps keep turf at a distance. This type of irrigation ring is not suitable for newly planted trees.
Newly planted trees
Newly planted trees need water close to, but not touching, the trunk. This is where all the roots are. As the tree becomes established and the root system spreads out, you can start using a trench irrigation ring. Of course, it’s a good idea to dig the trench before the tree’s roots reach that area.
In each case, the benefit to the tree is that water is allowed to seep into the soil slowly enough to be absorbed by the tree, rather than running off as urban drool, or percolating downward where tree roots cannot access it as well. And don’t forget to mulch under trees, keeping the mulch 6” away from the trunk. This will reduce water needs, thwart opportunistic weeds, and stabilize soil temperatures.
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