How to water trees during drought

Editor’s note: Get Growing, written by the La Plata County Extension Office’s Master Gardener Program, appears every other week during the growing season. It features timely tips and suggestions for your garden and landscape.

By Darrin Parmenter

As an integral part of any landscape, trees – despite their well-developed root system – can also succumb to drought stress. While symptoms of injury can be sudden – leaves wilting, curling, yellowing or scorching on the edges – the effects may not be seen for up to two years. Conifer needles can also exhibit stress by turning yellow, brown or even purple, and if the lack of moisture continues for an extended period, needle drop could occur.

Drought stress may also be a predisposing condition that sets the tree up for more serious infestations from pests or diseases in following years.

To keep your trees, especially those that were recently planted, healthy and growing, try following these watering techniques:

Deep water (12-inch depth below soil surface) up to three times per month, depending on supplemental precipitation.

Don’t stick the hose next to the trunk, but instead water the dripline, which is the outer edge of the tree’s branches.

Water slowly, allowing the moisture to percolate into the soil rather than having it run off.

Because the vast majority (90 percent) of the tree’s roots are in the top 12 inches of soil, digging holes around the tree to water deeply could harm those fragile roots.

How much water to use? Colorado State University Extension’s general recommendation is use approximately 10 gallons of water per inch of trunk diameter (taken at knee height) for each watering. So for a 4-inch-diameter tree, you would apply 40 gallons of water.

If you aren’t sure what the rate of water is coming out of the hose, then time how long it takes to fill a 5-gallon bucket with the hose. Then do some complicated third-grade math and you will have the time it takes to evenly distribute the water to the tree. You can also sacrifice a couple 5-gallon buckets by drilling out quarter-inch holes near the bottom and setting them, filled with water, under the dripline.

parmenterdm@co.laplata.co.us or 382-6464. Darrin Parmenter is director and horticulture agent of the La Plata County Extension Office.