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).
Living Wall Panel Indoor Planter << useful info. Ive seen great green wall planters yet either their placement or structure doesnt bode well for maintenance - and for example, the fact that some plants/succulents are going to grow to different sizes etc.