Keep the garden vertical. That's why it's good to look for shrubs and trees that max out interest as they grow up, not out. Try dwarf varieties for a small backyard, as well as more columnar evergreens (bonus—they boost wintertime interest, too).
Check out 44 Best Shrubs for Containers. You might know some plants and some may surprise you but one thing is sure- Youll like to have some of these shrubs right away in your container garden. - New Gardening Ideas
How to divide perennial plants and split oversize shrubs
Fatsia japonica 'Spider's Web' makes a wonderful specimen, particularly when planted near white-flowering plants that compliment the leaf variegations. It can also be used to help add light and colour to areas or lightly dappled shade.