All of my houseplants are potted in soil from my yard. Not recommended procedure, I know, but it seems to work just fine.
A couple of months ago I noticed one of the plants in my bedroom window had a little green friend growing next to it. Being of the pacifist persuasion, I let it be.
Recently I moved the leaves aside to give the plants a drink and I noticed a distinctive smell. A sniff of the fingers confirmed it - definitely a tomato plant.
The earth wants to feed us. We just have to step back and let it.