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Tuesday, April 23, 2013

Eliminating Lawn Can Lead to Problems for Established Trees

Q. I have a beautiful Loquat tree where the leaves have suddenly started to turn yellow and fell off.   Most of the fruit has also fallen off. The tree was located in the middle of grass. I had the landscape converted to desert rock in September. At the same time watering schedule was changed. I suspect it is being under watered. But before I increase it I want to ask if the cold winter we had here could have caused this yellowing.

A. Thanks for the pictures. It is probably not the cold. In a lawn situation the roots go everywhere and anywhere and usually spread to about 1½ to 2 times its height away from the trunk.

Loquat with rock mulch applied after growing in a lawn for a few years. In many cases the drip emitters do not
apply the water in the same places as lawn irrigation and the plant roots of established trees and shrubs die back.
This results in leaf drop and eventual die back of the limbs of established trees and shrubs.
            In drip irrigation we usually place the emitters a foot or so from the trunk. This bypasses about 80% of the root system it created when growing under a lawn.

            So, yes, it probably is drought but perhaps not because you are not delivering enough water. It is more likely that most of the tree roots are not receiving water. You can place emitters over a greater area under the canopy of the tree. But I would also reduce the size of the root system.

            Try root pruning the tree to reduce the size of the root system so it is closer to the emitters. Keep tree roots contained in the area directly under the canopy. Wet the soil thoroughly under the canopy and vertically slice the roots in a circle all around the tree at the edge of the canopy. This can be done with a sharpened spade.
Leaf drop of established loquat due to replacement of lawn with rock mulch and drip irrigation.

            At the same time, thin the canopy by removing wood. This reduces the tree’s demand for water. A tree that size will probably require 20 to 30 gallons each time you water. With the lawn now gone, the tree will actually use more water since the cooling capacity of the lawn has been removed.

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