It would be about the time to get worried. In the end, they are plants given intelligence through magic, so who can say if they possess anything resembling morals? At least they steal things freely, which is something Makoto doesn't do, so it's not like they would be copying her values, thus remaining harmless. It's possible Makoto is the only human they consider worth anything, in fact they view her as a goddess, which is even worse. They could start slitting throats in the darkness of the night.
But then again, this isn't written by Stephen King, so my worry is baseless.