If you’ve ever stood under a tree when it’s raining in Gilroy, you know much of the rainwater is deflected 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 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 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 like irrigation bags, but without touching the trunk.
Tree ring irrigation contraptions are DIY kits that create a singular drip tube for a tree, using adapters, tubing, and a filter. Like other systems, these are easily clogged, especially when you have hard water, as we do here.
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 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 about 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. As the tree becomes established and the root system spreads, you can use a trench irrigation ring. Of course, it’s a good idea to dig the trench before the 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.