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Tuesday, November 24, 2015

When Removing a Lawn, Large Trees Frequently Die

Q. We’re seriously considering getting rid of our turf and taking advantage of the SNWA Rebate Program ("Grass for Cash" Program).  However, not at the expense of our beautiful fruitless mulberry. What steps do we take to maintain the health and vitality of the tree? 
Mulberry that might be threatened in a "cash for grass" rebate program. Most landscapers will not provide enough water in the right locations for a tree of this size to survive.
A. Great looking tree and I applaud your efforts to keep it although I am sure those with severe allergy problems would like to see it gone.
            As you have discovered, the water needed to support a tree like that is nearly equal to the amount of water applied to the lawn underneath it. The best advice I have is to maintain the grass directly under the canopy of the tree. If you decide to remove all the grass, then you will need to add a way to deliver enough water directly underneath the canopy.
            A method that some people are using is to lay a coil of in-line drip emitters around the tree in a spiral, spacing the tubing about 12 to 18 inches apart. Use tubing with emitters spaced about 12 inches apart along its length.
            The less distance between emitters, the less time will be needed for watering. I am guessing this method will require about one hour to deliver enough water for the tree in a single irrigation. Other plants can be planted in this area that will take advantage of the wetted area.
            Another method, and the one I like the most, is to flood irrigate about half the area under the canopy with two bubblers in a constructed basin that is at least one third the diameter of the canopy. The basin must be level so that the water does not accumulate on one side of the basin.  It will take about 10 to 15 minutes to fill the basin with enough water to supply the tree.
Pine tree with a bubbler and basin used to for irrigation. The bubbler releases water quickly and fills the basin. It is important that the bottom of the basin is flat.

            The most common option is to use drip emitters under the tree. This seldom works when keeping large, mature trees like yours healthy. You would need a very large number of drip emitters to deliver enough water. Very few retrofitted desert landscapes use enough to keep the tree from dying back.  
This tree previously was growing in lawn. This area was converted to a rock landscape, the grass removed, to conserve water. This tree was not provided with enough water after this conversion so it began to die.

            Consider covering the soil under the tree with wood chip mulch rather than rock mulch to maintain good “soil health” under the tree. Good soil health was promoted in the past by maintaining your lawn. With the lawn gone and the soil covered with rock mulch, soil health will be severely impacted which will negatively impact the health of the tree in a period of 3 to 5 years.


  1. If the tree dies and it is contributing shade on your home on the summer, especially on the south or west side of the home, then whatever money you get in a rebate will quickly be eclipsed by the large increase in cooling bills annually.

    If you take Bob's advice and plant other things near the irrigators under the tree--which is a wise idea--you might have to select natives or approved plant list depending upon the terms of the incentive.

  2. We recently replaced ½ of our lawn with rock mulch and we have a beautiful 15 yr old Mesquite in the rock but near the grass. Reading your article about this situation will redouble my efforts to assure the tree survives.I didn’t realize it could take 3-5 yrs. to show signs of stress. Just wanted to say thanks and also hope I can continue to read your articles in the paper.

    1. Your welcome, Ed. Mesquite will have an easier time recovering than mulberry and should not give you as many problems with the irrigation. However, that tree will be used to lawn watering (shallow, frequent irrigations, constantly moist soils) so making the transition will be rough on it for a few years. Just make sure you provide water to it under its entire canopy area.