With few exceptions, herbaceous perennials require well-drained soil where they won't sit with soggy roots. If your garden is new, do recognize that perennials often grow rather slowly to full size. The second year, they creep. The third year, they leap. Soil preparation gives their growth the best support.
All flower gardens can happily include different types of plants.
Mixing roses, flowering shrubs, perennials, and annual flowers creates interest and provides year-round color. Annual cosmos grows well in the cool, sunny summers in western Washington, and provides armfuls of white, pink, and rose flowers for picking.