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Tuesday - August 02, 2011

From: Del Rio, TX
Region: Southwest
Topic: Watering, Drought Tolerant, Trees
Title: Dormancy in Pin Oaks without water in Del Rio, TX
Answered by: Jimmy Mills

QUESTION:

Can Pin Oak trees go dormant without enough water? If so how long can they live that way? Can they be brought back to producing leaves? If yes, then what do I need to do besides giving them water. I don't wont to cut them down if they have a chance of coming back. Thank you for your help! :)

ANSWER:

The short answer is yes, but they can also die without enough water.

But first, lets learn more about Pin Oaks Quercus palustris (Pin oak) . Clicking on this link takes us to its NPIN page, where we find that it is  a handsome lawn tree with shallow fibrous roots and high water use. Next, scroll down the page to the Additional Resources Box and click on the plant name beside USDA. This brings up the USDA Plants Profile page with a Distribution Map that indicates that Pin Oaks do not occur naturally in Texas. So we seem to have a tree in the wrong place, and perhaps, running out of time.

Plant dormancy is a survival strategy (see link)  that allows plants to live through unfavorable conditions. We most often think of it in the Fall where a series of programed processes take place that get the plant  ready for the freezing weather of winter. The most obvious results are the change of color of the leaves before they fall from the tree. The changing of the length of days and nights seems to be the environmental cue that triggers these changes.

Drought can also trigger dormancy as a result of stress on the plant due to a lack of water. One of the important processes that is going on in the leaves of the plant is photosynthesis which absolutely requires water. When water is scarce, the plant attempts to conserve water, and this can happen in at least three ways: the leaves can wilt, they can turn brown, or they can fall off. All of these shut down photosynthesis which reduces the demand on the roots for water.

What is the situation with your Pin Oaks? Are the leaves brown, or have they fallen off?  Before you proceed, you need to determine if the trees are still alive by applying what I call the “thumb nail test”. Locate a young thin  branch on the outer part of the tree, and scratch some of the bark off using your thumb nail. What you are looking for is green tissue. If you find some, that’s good news. If you don’t  move further down the stem and try again. Continue this until some green tissue is found. You’ll of course reach a point where the bark is too thick to scratch off with your thumb nail. If you haven’t found green tissue by this time, the prognosis is not good.

But let’s be optimistic! I’m including links to articles explaining dormancy, caring for trees in a drought situation, and watering tips to help you nurse your trees back to health.

Dormancy

   University of Alabama Extension

Tree Care

   centraltexastreecare.com

   Colorado State University

Watering

   University of Illinois





 

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