For what it's worth, I called a GM and asked about this issue.
I have 16 total characters and 13 of them garden. I send the harvest to my main and NPC everything except the crystals and the crap greens, which I sell on the AH.
I explained that I had 13 gardening characters and that I planned to NPC my harvest.
The GM told me not to worry about it. He/She said that banning doesn't take place in a vacuum -- that the STFU won't permaban without looking into things.
He/She further implied that those who believe they were banned for gardening were probably banned for something else. I can believe this, even with people saying they were told otherwise, because a while back my account was banned for (as far I knew) no reason. I called SE and the first person I spoke to told me I was banned for 3rd party tools. This was crazy, because I mostly played on console. It took several reps before someone said, "Oh, your account was hacked [it turned out to be ffxi atlas, btw] and the STFU will give it back when they're done with it." Took two weeks to get it back after that.
So maybe this is bigger than just gardening.
Here's the Conversation I had with the GM My best wishes to those who were banned -- for whatever reason. It sucks and I truly hope you can return.
~DW
Note: Yes, I am aware that GMs are not necessarily the final word and that they are in-game CSRs. I think we all know that, those of us who are reading this.