I tend a small, raised bed flower garden. It surrounds a maple tree on a sidewalk in Boston’s Back Bay.
It’s not an ideal gardening situation but the space gets great light and has been a joy to plant every year and see what grows.
Planting around a tree does take special care.
– Plant perennials that won’t interfere with the tree roots
– Never mound soil like a volcano around the tree trunk. That could suffocate the tree…
The best growers in my garden space are: pansies, petunias, salvia, (all currently in my garden), all types of ivy, dahlias, daisies, marigolds, mums and mandevillas. Those mandevillas were definitely the most show-stopping plants I ever grew. Among the disappointments, clematis (too fragile), geraniums (a complete disaster).
City Garden Ideas 
I just found your website today. Looks great to me. I’m looking forward to more information.