We have a large garden in Squamish, and are inundated with a weed that we think might be Angelica - low growing (up to 12") and invasive. It has a broad, entirely green leaf with three shallow lobes and serrated edges. It closely resembles another plant that has variagated green/yellow leaves, but the variagated one is not invasive and is easy to manage. We wish to isolate some of our areas from this invasion with a barrier of some sort. Our questions are: 1. How deep a barrier is needed in our silty soil to prevent the spread of this weed? 2. Does anyone have any suggestions as to a kind of barrier material that will be easy to install (we'll need a lot of it), effective, and not too expensive? 3. In some of our beds, we plan to kill it by covering the bed with plastic for a long period (after removing the good plants). How long will we need to keep it covered to be sure the roots are dead?