I have a prickly weed (a thistle?) that is invading my yard, see pictures. I have tried pulling them out, but they always return and seem to be multiplying exponentially. My theory is that they come back because they have a deep root system that is expanding under ground, and when I pull the leafy plant, the root remains and sends up replacements. My second attached photo shows a patch (about 5'x10') that had only a few thistles last year and is now full of thistles. How do I get rid of this plant? My thought is using an herbicide like Round-up, but am concerned about this approach--I hear bad things about using Roundup (bad for human health), and am also concerned that I won't be able to plant other plants in the bed after using the herbicide. What are your thoughts on the herbicide approach, and/or let me know other approaches for getting rid of this weed. Thank you!!