PlantLife Online

Answer

Ants are a natural part of any landscape and in most cases are not causing any damage. But to be sure spend some time in the garden watch where they go if they are marching up one plant in particular I would guess they are farming aphids. Check the underside of the leaves and where the leaves attach to the stem, aphids like to hangout there. No need for harsh chemicals if you do find any a mild soapy water solution applied with a hoes liberally to the plant every few days until they are gone will do the trick. A sticky substance or a black dust like film on the surface of the plant leaves is also a sign there are aphids. If the aphids are removed the ants will not have the food they need and carry on, if the ants are present but don't appear to be causing any damage I would leave it alone but keep an eye on it.