You are going to have to dig them out if you are talking about an herb or vegetable garden. They are going to be tough to kill with an organic product because of the round waxy like blades. And anything strong enough to really take it out, you don't want near your edibles. Yeah...probably not what you wanted to hear!
AAAAA they are so pretty but really invasive. I keep digging but they just come back for more. I will keep plugging away at them!!!