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. 

They lay mulch, plant plants, and take pride in the home.

I just read about the Shell Cracker Plant. 

There is nothing, at common law, that limits a profit a prendre to certain types of plants or lumber.

The tenant expressed interest in it, so I left it as the gift.I have also given a small plant on occasion.I always leave a greeting card.

That sounds like too much for me to spend right now.In addition, there is a clause in the tenant lease which states "Tenant shall conduct routine landscaping of the Premises, including regular mowing of the grass, removal of leaves and small fallen branches, regular removal of all weeds and grasses in landscaped areas and trimming of plantings, including shrubs, unless otherwise provided by the Owner or a third party such as a homeowners association."