Emerson from Newark De. writes
for years I have been doing it overtop the mulch and seen to get pretty good weed control, with rain in less than a week.
If you have had good weed control by applying over top, then that is still fine to do. As long as you water in the product very well, it should be fine. However, the preferred method would be to remove the mulch and apply underneath and water it in well and then cover it back up since the ground level is where it has to get to work.
Answer last updated on: 02/09/2012