I've noticed that there is NO gardening vendor in Marleybone. It's not really fair if a wizard is in Marleybone, but has all the gardening spells so far, and they want more. They would have to wait until Mooshu. Maybe you could add a vendor in Marleybone, carrying the rank 4 pest spell and some of the rank 3 grow spells, and leave the Mooshu vendor with the rank 5 pest spell and the other growing spells?
There are only Gardening Trainers in WC, KT, MS, and CL. I found the lack of Gardening trainers in each world odd as well, but don't really care if KI adds them since Gardening is a side venture and once you become a GMG aside from a little free gold, reagents, and cards it gets monotonous.