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Thursday - May 29, 2014

From: Austin, TX
Region: Select Region
Topic: Planting, Trees
Title: Adjustments to soil level change around tree from Austin
Answered by: Barbara Medford

QUESTION:

I am moving in to a new construction home in south Austin, builder has leveled the ground and sodded the front yard, I have a post oak in the front and because of the changes to the landscape the tree root flares are below ground now and builder made a ditch round that, now after every rain a puddle is around the tree and it stays for day or two, is it harmful to the tree? How to prevent that? Thanks.

ANSWER:

It's hard for us to comment on that method of saving a tree affected by changing levels around existing roots, so we are going to look first at previous questions to see if someone else on the Smarty Plants Team has had an insight that we don't. From Tequesta FL, Changing the Grade Over Mature Oak Roots. From there, we will go to the Internet. For your information, we will be searching on "tree well" as that is usually the technique used for protecting an existing tree when the ground level around it is altered. In one previous answer, we found this link to an article from Arborilogical Services on Dangers of Root Disturbance..

From West Virginia University Education Extension, here is an article on tree wells that has very clear instructions on how much dirt may (or may not) be allowed to remain over the roots, drainage, etc. From Texas A&M AgriLife Extension Protecting Existing Landscape Trees from Construction Damage.

That article first addresses exposing the tree roots with removal of dirt, and then addresses the problem of covering those roots with soil or grass:

"Raising the Grade:

Raising the soil level around a tree is the most

serious grade change. Air circulation is cut off and

moisture and nutrients cannot reach the tree roots.

In some cases drainage is greatly impaired and the

tree drowns."

From another previous question:

"An oak tree root system is extensive but shallow. The ground area at the outside edge of the canopy, referred to as the dripline, is especially important. The tree obtains most of its surface water here, and conducts an important exchange of air and other gases. Any change in the level of soil around an oak tree can have a negative impact. The most critical area lies within 6 to 10 feet of the trunk. No soil should be added or scraped away from that area. Construction activity is a great threat to trees. Do not allow any piling of materials, waste, etc. in the dripline area.

Paving should be kept out of the dripline and no closer than 15 feet from the tree trunk. If at all possible, use a porous paving material such as brick with sand joints, open bricks, bark, gravel, etc., which will allow some water penetration and gas exchange. Even with porous paving, the area around the trunk-at least a 10 foot radius-should be natural and uncovered."

Our summary of all this information is that, at the very least, you must provide drainage out of that trench. From the various sources we have provided you, we hope we have given you information you can use in your specific case. Without being able to see the space in question, we believe that there is too much obstruction over the vital tree roots to permit the absolutely necessary exchange of gases and nutrients.