Use materials that would absorb sound from bouncing around the room.... a busy plant next to the window, tapestry on the wall, rug on the hardwood floor.  

We invited tenants to come with us to the nursery to pick out plants and we paid for the starter plants.  

When I first leased up my 6 unit building in 2009 one of my original tenants asked me to plant a bush behind his unit to give him more privacy.

There was courtyard patio in the center of the building, and tenants could request to have planters assigned to them, so they could plant veggies or flowers, etc. 

After two weeks the tenant complained that there were toxic plants called angel trumpets in the yard and he would like them removed.

The real estate agent who I worked with to buy an owner-contract condo many moons ago, always sent her previous clients a poinsettia plant and a nice card. 

I'm not being snarky, I really don't see how growing plants would increase fire danger.

Would you require that they remove the garden and plant grass back where it was?

When a tenant asks if they can plant flowers, I'll pay for half of the perennials.

As soon as you close you should have your management change letter ready to post or nail and mail.I have a tenant now that I'm evicting for non-payment, but she is also a hoarder-type with trash and containers of plants outside her apartment that she refuses to move.