Answer: There are several products on the market that will kill broadleaf weeds such as pigweed without harming other plants, but they are specific. Since you didn't identify your groundcover, I can't make a recommendation - except to suggest that you carefully read the weed killer labels and make sure both amaranth and the plant you use as groundcover are listed on the label. If not, you risk killing your groundcover along with the weeds. Be sure to use in amounts and with the frequency as listed on the label. Best wishes with your landscape!
Q&A Library Searching Tips