The key to success with managing ants is that the queen ant must be killed. If she is not, the problem will not go away because she can keep making new worker ants. And of course, the queen ant is protected deep within the nest, so treatments like diatomaceous earth and vinegar, which must physically contact the ants to have any effect, won’t work. While I understand and support the goal of avoiding conventional pesticides, in the case of ants – and especially fire ants, which can harm people and pets – it’s best to just manage the job as effectively and quickly as possible with an ant bait. The great thing about using ant baits, though, is that they don’t pose a threat to “non-target organisms” (i.e., anything that’s not an ant) and since they are intended to be collected by the ants and fed to the rest of the colony, including the queen, they disappear quickly once they’ve been put out. Your plant won’t take up any residual from the treatment.