Irrigation in the desert

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As summer heat starts stressing the plants in our landscapes, it is important to know where and how deeply to water for optimum plant health.

The soil surrounding a plant's root system serves as a storage tank from which the plant draws moisture. The goal is to water the root zone where most water-absorbing or "feeder roots" are found. This is usually in the top 8-24 inches of soil and out one and one-half to four times as wide as the plant's canopy.

How deep should you water?

Smaller plants usually have smaller root systems. Water perennials, annuals and vegetables to a depth of 1 foot. Water small to medium shrubs and large groundcovers to a depth of 15 inches. Water large shrubs and trees to a depth of 18 to 24 inches.

It helps to use a soil probe to monitor how deeply you water. This could be a purchased product, a piece of sharpened wood, metal such as rebar or a long screwdriver.

A purchased soil probe pulls out a core of soil and you can look at the depth the water reaches by examining the core. A stick or metal bar will slide easily through wet soil, but become difficult to push into the ground as the soil dries out. You might want to put inch marks on your probe to make an easy-to-read depth gauge.

To test how deeply the water is penetrating, water your normal cycle, and then go out after 24 hours with your probe. Once you have determined how long it takes to fill a root zone, irrigate that same length of time each watering session.

How wide an area should you water? Wider is better, all the way round a plant.

A 2-inch increase in diameter of watering area translates to a 44 percent increase in coverage. This increase in irrigated area allows a plant to increase its root zone. A larger root zone results in a stronger, healthier plant and means more flowers, more shade, more fruit and more veggies.

As shrubs and trees grow, apply the water near the outer canopy rather than right at the trunk. Feeder roots are located out from the trunk.

In our arid climate, water is life because plants will not survive with inadequate irrigation. Be water wise. Make every drop count.

This information comes from "Desert Landscaping for Beginners - Tips and Techniques for Success in an Arid Climate" by the Arizona Master Gardeners of Maricopa County Cooperative Extension.

For information, contact me, 775-887-2252 or, your local University of Nevada Cooperative Extension office or at "Ask a Master Gardener" at

• JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.


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