would i have to wait for the slut route and the Max hearts, or can I talk to anna about the garden
Basically you have to allow Anna to fully embrace her sexual desires, which can be done by choosing the Slut Route and get her to 5 Hearts since you have to Share her with everyone else.
Only by then, you can do the Sharing Route with Master Zhen
Just an opion. I did the slut and sharing route, Imo the pure route or harem route is the best