That is a scam, there is no such thing as a Grower's Certificate. That is a way for some rip-off clinics to get more money out of you. There is nothing in the law that describes such a thing, it has been proven that the law does not recognize it.
The law in your county or city is what local law enforcement will use as a guideline. So what matters is how well you can talk with them. The plant guidelines that were described in SB 420 of 6 mature or 12 immature plants per patient have been struck down as unconstitutional by an Appellate Court decision, "the Kelly decision."