I have an 8 year old Colorado blue spruce with 2' tall quack grass growing up through the bottom branches. If I pull the grass out it comes back thicker. I cannot dig it up as the roots are up to 15' long. I thought about cutting the bottom branches off the spruce and spraying Round Up on the ground to kill the grass but not sure. Can anyone help with killing this grass?
I have a quack grass problem, too. Ordinary methods will not work. I killed a whole bed of roses to get rid of it. A friend said she fills the little plastic florist containers that keep roses hydrated with full strength RoundUp concentrate and attaches one to the end of each of the long grass runners. This will kill the roots of the grass without injuring the tree. Good luck.
I would not use Round Up, as I'd be afraid it would hurt the tree. I would pull out all you can, then add a 3-4 inch layer of mulch to smother the grass. May take a few times, but it should help.
Not sure on this, but my landscaper suggested we use Preen (name brand) for killing weeds around our bushes. Maybe check out the label at your local home improvement store.
For killing weeds & grass, Vinegar, put into a plant spray is one of the best there is! ...In fact, you can heat it up because the hotter it is, the better it works. For really tough areas, you can buy a much stronger Vinegar at a plant nursery... This way, you can choose to add water or not, depending on the situation.
A second idea is to first weed-wack the area, then put weed cloth down... or just cut a hole & a slit into a plastic garbage bag or a tarp & put this around the treetrunk & over the grass for a week or two to kill it. (The hole & slit are to fit it around the tree trunk) Then after the grass on top has died (the roots haven't) then cover the area with garden cloth so the tree will still be able to get water.... Be sure to hold the tarp & weed cloth down with rocks or bricks... If you like, you can even cover the garden (weed) cloth up with bark or mulch of some sort, but there's no need if you can't see it because it's below the tree branches anyway...