Do you have the annual flowering type or the evergreen groundcove? Both go by the same name.

Last year my annual vincas died off earlier than I thought they should. I had some ants mining the pots too. Before that, I'd managed to have the white bloomers last all year round. Could be the ants are aerating the soil around the roots.

If I have things in pots, I don't hesitate to use the Sevin dust. I don't put it out in the garden in general though, because I don't want to kill off the lightening bugs which are making a comeback.

You might also consider using the garlic water for those pots, and see if that helps get rid of the ants.
Just a thought.