Creating a perennial garden is a wonderful investment that you will enjoy year after year, so it is worth taking the time to plan a layout that will optimize your space and allow you to enjoy colorful blooms throughout the spring and summer seasons. For the best result you will need to consider each flower's width and height at maturity, the color, and the bloom season so that you can create a garden that is complimentary and long lasting.
As you plan your garden think about the viewpoint from which you will be enjoying your garden the majority of the time, and design the layout so that there are taller plants in the back with tiered heights and color to the front where the shortest plants will be placed. Consider leaving some space for a border of annuals that can be refreshed throughout the spring and summer months for additional color.
Although you may be tempted to fill the bed right from the start, it is best to apply some patience and pay attention to how wide the perennials are expected to spread. If you don't favor the wild, natural flower garden feel, you will want to leave ample space between each plant so that some mulch will remain visible between your flowers in future years.
Think of your perennial garden as a canvas. You can focus on creating a simple look with similar colored flowers accented with plants that have interesting foliage, or you can plan to have a rainbow of bright colors that change continually throughout the seasons! If your garden bed is primarily in the shade your options will be much more specific to what can thrive in your space, but don't worry there are plenty of interesting things you can do with shade favoring plants.
If you are anything like we are here at Dambly's, you spend the winter anxiously awaiting the first glimpses of spring color! As you plan your garden you will want to keep in mind that many of the most striking flowers have very specific bloom times, so you will want to choose a variety of plants that bloom at different points in the season so that you are always enjoying some color. Creeping Phlox and Iberis will give early color to your garden, and staples like Stella D'Oro Daylilies will give you long lasting color starting in June and carrying through the summer months. If you have plenty of room, you may want to consider a back drop of some flowering shrubs that will provide a foliage element all season, but can contribute summer color as well (like the Knockout Rose, Endless Summer Hydrangea, or Butterfly Bushes).
To help you plan out your perennial garden here is a chart of common perennials by height and bloom season: