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Wednesday - July 03, 2013

From: Austin, TX
Region: Southwest
Topic: Diseases and Disorders, Planting, Pruning, Trees
Title: Oak roots damaged by ax from Austin
Answered by: Barbara Medford

QUESTION:

Hello. I am attempting to create my own tiny copy of the Wildflower Center within my yard. I'm using all native, drought tolerant plants. My front yard is full of live oaks. I used a sod cutter last weekend to dig out new beds and extend others. One of the new beds is circled by 6 live oaks. I thought I could fill it with shade growing plants like caladiums, turks cap, blue daze, and etcetera. They are growing wonderfully under another live oak. Yesterday I tried to plant and the root structure through that whole area was impossible for me to penetrate. I even tried using an ax. I never made a dent so I gave up cuz I wasn't sure if I should even be doing that to the root system. Now, I have read information you have provided here and realizing all too late that I should have left it as is and that I may have harmed the trees. It's June. Did I just injure or possibly destroy these lovely trees? Do I need to do anything to treat the area I tried to dig into? It's a large area. Should I recover it with St. Augustine? Should I just mulch with bark and leave alone? or should I plant some honey suckle outside of it and let it make its way across? There is a hill to one side of them so I cold conceivably plant those at the bottom of the hill.

ANSWER:

What you should remember about creatiing a mini-Wildflower Center (although we are truly flattered) is that it was built on a moderately bare, rocky ground and opened, much smaller than it is today, in 1994. Some existing large trees were saved, and still today, the large trees, both those planted after the Center opened and the legacy trees still there from longer ago, are considered treasures. Conclusion: Before you plant, cut, spray or even buy any plant, large or small, native or weird, consider the consequences. Every single plant that went in to the Wildflower Center or that was removed, for whatever reason, was given serious consideration by professional staff and experienced volunteers. This still goes on today, with the new Arboretum and the soon to be opened Lucy and Ian Family Garden. Those gardens did not become beautiful gardens with plants in the shade of large trees overnight.

You need to remember that the roots of a tree can extend underground for 2 to 3 times the circumference of the upper crown of the tree. With several trees all together in a circle, as you describe, there is obviously an absolute mat of large tough roots underground. So, you know now that you can't grow the sort of plants in there that you want to, but do you know all the reasons why you can't?

1. The competition of the roots with anything you are trying to establish; we are betting on the tree roots in that war. Most tree roots grow near the surface or even show above the surface of the soil, in order to make gas exchanges of oxygen, as well as obtain nutrients and water. Those roots do not play well with others.

2. The shade of a tree that is heavily leaved almost year round. Most blooming plants require at least some full sun during the day, and some may survive but not bloom at all in deep shade.

3. Allelopathy. This is a defense mechanism that is employed by some trees, including oaks, as well as pecans, black walnuts, hickory and others, that is aimed at eliminating competition from other plants beneath the tree. This substance emitted by the trees can be in roots, twigs, acorns and leaves.

So, you see, even if you had not taken an axe to the root most, if not all, of those understory plants would have likely not survived, anyway. So, now you know something about making decisions when you are gardening. Your question was, "Now what?" We don't know which of the many trees with the common name "live oak" you have, but it's a good possibility, in Austin, that it is Quercus fusiformis (Escarpment live oak). Doesn't make a whole lot of difference, but all "live oaks" are much more susceptible to Oak Wilt. Follow this link to a previous Mr. Smarty Plants answer on oak wilt, and follow even more links in that article. We have answered so many questions on damage to live oaks makng them susceptible to Oak Wilt that we really can't type it all again.

We don't know if you axed just one place or all over everywhere. The fact that you gave up is probably the best decision you made that day. We don't know if those cuts are exposed to the air, or if you put any pruning paint on them. You will have to be the judge, from the material we have given you, of how drastic your situation is.

Arborilogical Services Dangers of Root Disturbance

John Droomgoole's Natural Gardening Live Oak Tree Pruniing

What we are hoping is that the tree will be all right. What we suggest is that if the cut is exposed above the ground, you paint it with pruning paint. If it is still at ground level or below, we suggest you cover it with good soil, not too deep, and cross your fingers.

One last word: Don't do it again.

 

From the Image Gallery


Escarpment live oak
Quercus fusiformis

Escarpment live oak
Quercus fusiformis

Escarpment live oak
Quercus fusiformis

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