Grow for it, Dizzy for Dsny!
There are lots of perennials suitable for container planting, and just a few suggestions for sun and long bloom time would be:
Blanketflower (Gaillardia)
Daylilies (Repeat bloomer, staggered bloom times)
Speedwell ( Veronica, Sunny Blue Border, is a nice choice)
Coreopsis
Shasta Daisy (Leucanthemum, Becky)
Pincushion Flower (Scabiosa)
How about roses? -
~Growing Roses in Containers~
These are just a few ideas. A trip to your favourite garden centre/nursery and a chitchat with a knowledgeable employee would also give lots of great ideas. You might also want to pick up a book on container perennials.
I know you're looking for blooms but some of the dwarf grasses would look great too.
A few things to keep in mind when potting perennials, is their mature size and moisture needs. You need a pot that drains well and will fit the plant (and it's root system), when it's grown. Putting different plants together can work, but only if their wet/dry soil requirements are compatible. Also, one plant can overpower the other.
Since your containers could be large (and heavy), and you'll want to be able move them, lightweight planters, or planters on casters might be a good idea. Terra-cotta and ceramic pots may crack and break if left out in the winter, full of soil. Not all perennials can survive winter in a container, and may need to be removed and planted in the ground (heeled in). We do this with our container hostas and ferns. Our container hydrangea we put in the garden shed, and it seems to have survived. An unheated garage would work also.
Good luck, and let us know what you decide to plant!
