He even had flower planting on one bill.

Other times of the year - if you find out your tenant is recovering from a surgery, have a flower delivery service drop off a $30 "get well" flowers - just did that one this week.

ie, do they want a stump dug out or a little flower bed cleared or?

I'd even think outside the box and give every tenant a small gift of appreciation - a cake, flowers, gift card, etc.

I have a rental and I am wondering if I can depreciate mulch, gardening soil, annual flowers and perennials? 

We don't have one plant closed that 3 feet from any structure and every plant and tree we have is in flower pots.It took me several years to think about removing all the grass from every property because we always maintained our lawns to the point they were beautiful and weedless.

In some jurisdictions you can drain the gray-water into a flower bed.

This usually involves fresh mulch, flowers, etc. 

Also, all of our other properties have maintenance that needs to be done so we'll be very busy bees flitting from flower to flower.

Very few people are going to avoid someone who shows they can be an asset to their team because they have some flowers on their hands.