hi.
i haven't really looked into it much, but i don't think i can prove that it's the plants - just because ants and plants are both everywhere. even if the plants did attract them, i have little faith that removing them will take them away. and, honestly, that wasn't really what i was thinking. if it was roaches, i'd be a bit more concerned about the plants, but not ants...
my hypothesis is that it's related to the weather. it's been an unusually cold and wet summer. ants like it warm and dry. so, the cold and wet soil has led them to migrate, and they ended up in the house. it's less a pull hypothesis and more a push hypothesis - it's less that something is attracting them to the house and more that the weather is forcing them to explore, and they happened to stumble upon the house.
that said, something else that's recently changed is the barbeque in the front. and, i don't think i need an article to prove that ants are going to want to be around where there's a barbeque, as anything that gets dropped will become food. further, you can clean a barbeque, but you can't *really* clean a barbeque. maybe you could ask if they've seen ants around it and keep an eye on it.
but, again, i don't think that's the reason. i think it's the weather.
there's a study here, but there's lots of more info on the topic out there:
http://news.stanford.edu/pr/01/ants45.html
i think the only option is barricading them out. and hoping it warms up soon...
j