My soil is infestated with ants too. I hope that's not a sign of aphids. Didn't know there was a connection. They like flowers too especially paeonies. Anyway, I've tried pouring boiling water on them which puts a dent in them. Mule team borax on the soil helps. They carry it down to the bottom of the anthill and it is toxic to them. The most effective for me has been the ant traps with a poison inside them. The ants go inside and get the poison. It kills off the adults. Two weeks later the babies hatch and you will find a new infestation of tiny ants but once they get the poison they are gone too and the whole hill is taken care of.