Why are the ants there? Ants, as a rule, are part of Ma Natures recycling team, not a problem that needs to be eliminated. If there is a large number assmebling in one place there is a reason and the gardener needs to look closely to see what that is.

dadri, ants are happy to explore and even settle in newly distrubed soil. Seeing an increase in ant activity in freshly tilled gardens or around newly installed plants is expected, and not usually anything to worry about.

Please know that ants and aphids don't necessarily go hand in hand. Inspect your roses frequently for aphids and keep them washed away. As for the ants, unless you have a large colony building up around your roses, I don't think I'd worry too much.

If there is a problem, try discouraging them by drenching the colony with water. Since you don't have the southern fire ant where you are, I don't think that any ant bait (even an organic one) is needed.