If you’ve ever stood under a tree canopy when it’s raining, you know that much of the rainwater is deflected away from the trunk by the leaves. This protects the trunk from moisture that might cause rot or fungal disease, while allowing rainwater to reach roots.
In the past, it was common to plant trees in depressions that were filled with water to irrigate the tree. We now know that this is a bad idea as it exposes the trunk to too much moisture. Instead, it is the roots that grow beyond the canopy that absorb the most water. You can mimic this action by providing irrigation water in a ring at the drip line of mature trees.
While you can certainly water your Morgan Hill trees with a hose, irrigation rings save time and provide the water more slowly, preventing runoff. Irrigation rings come in many forms:
Irrigation bags are large bags that wrap around tree trunks and slowly deliver a specific quantity of water. These are especially useful for large plantings. The bags must be removed when not being used to reduce moisture buildup and to facilitate respiration.
Ooze rings work similarly to irrigation bags, but without touching the trunk.
Tree ring irrigation contraptions (TRIC) are DIY kits that create a singular drip tube for a tree, using adapters, tubing, and a filter. Like other drip irrigation systems, these are easily clogged, especially when you have hard water, as we do here in the Bay Area.
Soaker hoses can be spiraled around a tree, starting from the middle of the tree’s canopy and ending just beyond it.
Or, you can simply to dig a shallow trench, four inches 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 eight feet across, and a trench four inches 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 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.
Irrigation rings are handy tools for preventing shade tree decline and conserving water. And don’t forget to mulch under trees, keeping the mulch six inches from the trunk. This will reduce water needs, thwart opportunistic weeds, and stabilize soil temperatures.
Kate Russell is a UCCE Master Gardener in Santa Clara County. For more information, visit mgsantaclara.ucanr.edu or call (408) 282-3105 between 9:30 a.m. and 12:30 p.m., Monday through Friday. Stop by the Spring Garden Market between 9 a.m. and 2 p.m., April 13, at Martial Cottle Park for all your spring planting needs.
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