Q: We excavated a trench for drainage near an oak tree. At the closest point, we are maybe 12 feet from the trunk of the tree. We did not break any roots larger than about 3/4 inch. Will the tree live? Is there anything we should do for the tree and or roots? — Matt Davidson, email
A: The trench has severely compromised the tree’s health. The critical root zone of a tree can be calculated as the diameter of the trunk measured 4.5 feet above the ground in inches times 1.3. The result is the radius of the circle around the tree that contains the critical structural and feeder roots. Damage to more than 30% of the critical root zone will result in canopy loss, reduced vigor, and the potential for the tree to fall.
Looking at your photo, I estimate the tree trunk is 18 inches thick at 4.5 feet above ground. Multiplying that diameter times 1.3 yields 24 feet, the radius of the critical root zone. You definitely dug in the critical root zone. Though you didn’t get closer than 12 feet, your trench’s path curved past the tree, making the damage more significant. There are still good roots on the back side of the tree, but damage has certainly been done to the structural roots on the trench side. I highly recommend you consult an expert certified arborist through the Georgia Arborist Association, georgiaarborist.org, or the American Society of Consulting Arborists, bit.ly/GAarbconsult to determine what to do.
Q: I have a large pine straw bed that is spongy to walk on. I thought it was excess water and wondered where it could be coming from. I believe I have voles. Should I treat the pine straw area with grub killer now? Or what should I do? — Mary Greer, email
A: Why would you apply grub killer? Do you see any damage to your plants? Voles chew on the roots of plants; they don’t eat grubs. Voles prefer to live and run under mulch, gnawing on the roots and bark of small plants right at the soil line. Vole tunnels are not underground; they use pathways hidden by mulch or vegetation like tall grass or ground cover plants. When voles do tunnel, it’s next to the trunk of a plant as they try to get down to the root system to feed.
I think you should watch for damage at the base of nearby plants, particularly damage that makes plants lean or break off. This usually happens in spring, but voles actively feed all year. If you find damage, set several mouse traps baited with peanut butter randomly in your garden. Cover each with a cardboard box to deter birds from the traps.
GARDEN QUESTIONS? Send them to Walter at georgiagardener@yahoo.com. Questions with good pictures, if appropriate, are preferred but not required.
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