Question
Peter:

Thanks for reading my question.  I have a 14 foot tall Red oak and two 12 foot maples that I planted last summer.  All three trees are planted in grass that is water by usual lawn irrigation sprinklers.  I mounded each tree, as instructed and incorporated proper amendments into the soil.  Each tree appears to be doing well.  I've recently added bark to the base to keep the grass from encroaching on the mound; however, this isn't very effective.  

My question to you is this:

Is it safe for the tree if I "lightly" spray round-up on the grass that is growing into the dirt around the base of the tree?  I've seen many office sites with trees that have no grass growing (or recently kill grass) and I would like to keep my trees' root ball area free from sod as well.

I recognize I should not disturb the roots at the base so I don't want to aggressively pull any grass with any  type of tool.   My concern is that round-up might be absorbed via the roots and damage the tree.  If so,  do you have any other suggestions how to keep grass from growing on the base?

Thanks,


Trevor Hanson
Denver  

Answer
I would suggest that you put a border around the trees and then cut the grass off with an edger. This will prevent the grass rhizomes from "running" into your cleared area. You could use a concrete curb, bricks, landscape ties etc. Just putting bark on the grass, you will end up with grass growing though the bark mulch.

I wouldn't be too concerned about pulling the grass out if you do it by hand. You aren't likely to damage the tree roots, they are down lower and should be pretty well established by now. I wouldn't use a roto tiller, but hand tools should be OK.

As far as Roundup, it needs to be translocated, therefore it has to go onto green vegetation. Once it hits dirt, it locks up with organic soil particles and becomes inert. So in this application, I would say you are pretty safe. Try and avoid any overspray, or you will have dead spots on your lawn.

I would suggest you border the tree, pull out most of the grass by hand and then spray the remainder. Then you can put landscape fabric down and bark mulch over that.