Answer: In my experience the most effficient method is to treat it with glyphosate, being sure to follow the label instructions very carefully. This is a non-selective herbicide and will damage neighboring plants if allowed to contact them. You can use a piece of cardboard or plastic as a screen against accidental drift and be sure to work on a very calm day. Some gardeners also report success using the wipe application method when working in tight quarters. Alternatively, you can try to "smother" it over time by covering it with a thick layer of cardboard or newspaper topped with a thick layer of mulch. You could also try repeated hand weeding, but this is very time consuming when faced with an extensive and thick planting.
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