I'm growing a mint plant, among other things (yes, I know it will probably take over, that's fine, more mojitos!). It's a balcony garden; the planter is built in along the railing.
There is a family of ants that has moved in. They constantly crawl all over the roots of the mint plant, and at any given time, there are several ants hanging out on the bottom of most of the leaves. I don't know what they are doing there. They don't appear to be eating the leaves, but are they somehow stealing minty-ness & flavor from the plant? I haven't used too many leaves yet, because the plant isn't that big, but I don't really want to be shaking off tons of ants every time I want some mint. They don't care at all about any of the other plants (mostly flowers, some thyme).
Everything I read online says that mint repels ants, so I am very confused as to what they are up to... Has anyone seen this before?
Have you examined the leaves/stems for the presence of sucking insects like aphids, scale, mealybugs, etc? Typically when I find ants crawling on a plant it's because one of those pests is present (they secrete honeydew which the ants like). I've found that ants will take up residence in planters, garden beds, etc in the absence of aphids, etc but I don't see them on the plants themselves then, I only notice them when I water the area and they all come up out of the nest to keep from drowning.
There are lots of little green dots on the bottom of the leaves the ants like, which I think are aphids... Now, what should I do about it? I've cut off the branches with the main concentrations of aphids...
I don't like to use chemicals at all in my garden, so I manage aphids with a strong blast from the hose, repeated every day or two until they go away. You could also use insecticidal soap or pretty much any pesticide that you want. Aphids are easy to kill because they're soft-bodied, but they can be hard to get rid of because they reproduce very quickly. If you miss even one or two and then don't look at the plant for a week, you'll find your infestation is back. So no matter what method of control you decide to use, you need to stay on top of it and repeat fairly frequently until you're sure they are gone. There's no need to cut off the infested branches, and even though you've done that I'd still do the blasting with the hose or spraying with your pesticide of choice because otherwise the ones that are left on the less infested branches will just keep multiplying and soon those other branches will be just as bad.