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Mr. Smarty Plants - Yellowing of leaves in Texas Mountain Laurel from Austin

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Monday - June 25, 2012

From: Austin, TX
Region: Southwest
Topic: Diseases and Disorders, Watering, Shrubs
Title: Yellowing of leaves in Texas Mountain Laurel from Austin
Answered by: Barbara Medford

QUESTION:

I planted a Texas Mountain Laurel in my Austin, TX yard this January. The tree was good sized (about 5 feet tall) when I planted it. Recently the leaves of the tree have started to turn yellow along the veins of the leaves, with some of the lower leaves turning a pale mottled yellow color. This is in distinct contrast to the dark glossy green of other established mountain laurels in my neighborhood. The tree receives full sun from mid-morning until evening. I have been watering the tree to help it become established. Am I overwatering the tree, or not providing enough water? Do I need to provide some shade until the tree is established? So far there hasn't been any leaf loss, but I am concerned that unless I do something the tree will not survive.

ANSWER:

We are assuming that the leaves of the mountain laurels in your neighborhood are on trees that were not planted so recently. The difference in yours, although you planted it when we recommend for woody plants, in Winter, may be transplant shock.

Yellowish leaves could indicate chlorosis, or lack of iron being taken up by the tree from the soil. This is often caused  by poor drainage and/or dense clay soil, which causes water to stand on the roots. Again, this could  be a problem caused by planting, perhaps without any organic material added to hole, or damage to the tiny rootlets that take up water and trace elements, including iron, from the soil.

Please read this article from the University of Illinois Extension on chlorosis. Note the comment that the presence of chlorosis is often due to high alkalinity in the soil. You can be pretty sure that your soil is alkaline, but the Mountain Laurel is native to that soil and ordinarily would be happy in it.

Among the steps we would recommend are to use some sort of iron supplement, not too much, as Sophora secundiflora (Texas mountain laurel) does not ordinarily care for fertilizer. Water less, because we believe the main problem is lack of drainage in the hole dug for the shrub. Watering once a week should be adequate. Water by pushing a hose down into the soil around the tree and letting it dribble until water comes to the surface. Finally, using a good quality organic mulch, spread the mulch over the root area without allowing it to touch the trunk area. This will protect the roots from heat and cold and, as the mulch decomposes, will add some material to the soil to assist in drainage.

 

From the Image Gallery


Texas mountain laurel
Sophora secundiflora

Texas mountain laurel
Sophora secundiflora

Texas mountain laurel
Sophora secundiflora

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