February 2001, Volume VIII, Issue No. 2

Water for Irrigation
Hard Water, Hard Times

David M. Kopec, Extension Turfgrass Specialist

Last month's Newsletter addressed salts in irrigation water. This month's issue deals with the water issue of "hard or soft."

As mentioned previously, salty water is different from "hard " water. Many homeowners do not make this distinction.

The salt content (salinity) of water addresses the sum of all the dissolved mineral elements in the water. "Hard" water addresses the amounts of calcium and magnesium in the water. The amount of the total calcium and magnesium alone determines whether the water is "hard"or not. The concentration is actually measured in parts per million, milligrams per litre, or in older units, called "grains." The higher the value, the greater the amounts of calcium and magnesium.

The classification is as follows:

Water Class PPM Grains

Soft 0 - 60 0 - 3.5
Moderately Hard 61 - 120 3.5 - 7.0
Hard 121 - 180 7.0 - 10.5
Very Hard > 180 > 10.5

Is hard water bad for lawns and landscape plants? NO – it's good!

Calcium and magnesium in the water help counteract the sodium in the water. Calcium and magnesium in household water make soap hard to dissolve. Over time, they can form deposits inside pipes, especially if they are made out of galvanized steel. That's why people switch over to water softeners. Here's how a water softener works:

A softener adds sodium to a large tank of water. Inside the tank, the sodium replaces the calcium and magnesium that already exists in the tap or well water. This makes the water "soft" for household purposes.

While this is good for water use inside the house, it makes things bad for use outside the house. The "new sodium" from the water softener can lead up to a build-up of sodium in the soil which supports the lawn and landscape plants. While the absolute amount of sodium itself may not harm the landscape plants itself, sodium build-up in the soil degrades the soil structure. Moderate to high sodium levels in the soil causes the soil to lose its ability to form small clods. The soil becomes dispersed and flaky. The "flaky" condition causes poor water infiltration, and starves lawn and plant roots for oxygen. It also increases irrigation run-off as well.

If you use a water softener and irrigate the lawn and landscape plants, here's
what to do:

Twice a year apply agricultural-grade gypsum to the lawn at the rate of 2.5 lbs per 100 square feet (10 x 10 feet) area of the lawn. Water it in. It won't burn the lawn.

For landscape plants, apply gypsum at the rate of 0.75 ounces to every square foot of understory canopy space that gets irrigated. This may be as little as 4/10 lbs. of gypsum for a small shrub (4 x 4 feet) area, or 6 ½ ounces. For a 15 x 15 feet tree
-well, apply 5 lbs. Of gypsum.

Gypsum takes months to dissolve and do its job. So, keep watering as usual, and the gypsum will do its stuff. Gypsum is (essentially) dirt cheap, so don't worry about the costs – better safe than sorry!

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Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.

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