NL is meant as Netherlands here and the context is that since you can't talk about growing cannabis in the open, people talk about their "vegetable" gardens or "herbs" instead. The comment you're responding to is implying that the grow tent is used to grow cannabis but he's covering it up by saying it's a vegetable garden.
Almost: if it were NL I would imply that it is to grow cannabis but since the OP is obviously 100% sincere I don't doubt they're doing the legit thing.
