Mint Plant Attracts Ants
Can you tell me why a mint plant would attract ants? This is your standard mint julep and planted recently in a 12 inch diameter container. I had the same problem last year and would water the plant to drown the ants and also keep water in a pan to keep them from crawling into the pot. Are these sugar ants? Will they destroy the roots?
There are many species of ants and cannot say from your description. Check the mint plant for aphids. They are a soft bodied sucking insect which exudes a honeydew as they feed. This is sugary and ants can be attracted to this. Hose the plant off with a forceful spray of water if you notice them. http://extension.umd.edu/hgic/aphids-flowers
Do not overwater. If you keep water in the saucer to deter the ants, elevate the pot above the water so you do not drown the roots.
Also, the ants may be nesting in the soil. Knock the plant from the container and check. If so, you will have to repot using fresh potting mix. You can lay some outdoor ant baits around the base of the container.