How can I get rid of goutweed? I've tried ripping it out, smothering it with black plastic but it continues to suffocate other plants and take over the garden bed.

I would suggest that you use Roundup on the gout weed, other than keep pulling it up there is no other answer i f it is near other plants then Roundup will kill anything green that it touches and you might have to use a paint brush and paint it on the gout weed only. It is a hard weed to control.