Maybe you could add it in with the painting/guitar exploits.
If the only objection to gardening is how it will affect lot values there shouldn't be a problem gardening on public or empty lots (without houses) because we can't move to those so you wouldn't be affecting the value of any relevant lots. But if the issue is also that its kinda exploity since you get all the benefits of gardening without having to do the weeding/watering. I actually didn't know that you could plant on public lots or in other people's gardens but then again it never would have occurred to me to try.
Are we allowed to stock ponds? Either on public lots or private lots that have ponds, afaik it doesn't affect the value (I will check).