I've got a customer who i started mowing for when i was in highschool. It was a newly constructed home and they had a bunch of tree's planted. The planter raised them up a little bit since the lawn isn't flat and put down a thin level of pine bark chips. At that time i didn't really care what happened to the trees, and i just mowed around it and trimmed. Over the years the pine chips have gotten displaced from weed whacking around the trees, and now there is normal grass growing on the tree ring. Trimming all the tree's is a major PITA, so i'm going to suggest that we (I) do a mulch job on them. What should I do about the grass that is growing there now? should i just get as close to the dirt as possible with the string trimmer and then lay 3" of mulch down on top if it? or will the grass come up through it? (Keep in mind its not just a couple blades or weeds, its just about as thick as the lawn.) It's going to be 35-40YD of mulch, so i want to make sure i do it right the first time so i don't have to weed it all out again in a month.