Naturally made, yes. the specific process called "grown" would better apply if there was, say, a plastic bottle-fruiting plant, but whether that plant was designed by humans or simply found by them in the environment does not change whether it is natural.
There is no such thing as natural versus unnatural, this dichotomy is a holdover from the time when we believed there was another plane of reality outside or distinct from the "natural" universe, which was somehow tainted by flaws unique to humans, being creatures with one foot in both realities.
I realize it sounds like a technically correct Internet argument of the nitpick variety, but I think that the norm of asseting an unchallenged bias toward "natural," and against "artificial," could use a general reassessment as it is constantly exploited by people using this ultimately baseless distinction as a way to bias opinion uncritically toward one kind of behavior or another.
so my plastic bottles are naturally grown?