There are certain perennials that I like to call "Workhorses". They work in a variety of Zones and are hardy, dependable bloomers. For example, the Balloonflower and Bellflower (they're related, more on that below) are quickly becoming a staple in my garden as they can be counted on to bloom from June-September.
Both the Bellflower (Campanula) and Balloonflower (Platycodon) are members of the Campanulaceae family. In layman's terms, they're cousins. What's the difference? The Bellflower is smaller (on left) and the Balloonflower is a larger bloom (on right).
Please excuse the lack of blooms, these guys were just planted in July and are going through "settlement shock" as I like to call it. It always takes 1-2 seasons for my plants to settle in and start growing.
-Blooms June through September
-Comes in a variety of subtle "cottage garden" shades (white, pink, purple)
-Good size for the middle row of your garden (can grow to a height of 12" to 36")
-I do recommend deadheading them once a week or so.