For all season bloom it is important to use the art of peeking, especially in a small garden. Sometimes it begins as an experiment to see if it works, like my plumbago under my daylilies. Then there are some peekers you know will work such as Broadway Lights Shasta taking over for Red Rum Daylily (which will be cut to the ground when done blooming - will get a flush of new leaves but not as tall).
Gaura will bloom all summer from behind the impatiens, daylilies will bloom inside the Shastas, behind the roses. Annuals in pots can peek out anywhere you need them, moving them if need be. Nicotiana will take over for the daylilies by Rozanne and Perilla will grow quite tall to fill in around the Dahlias. It's like a game called "What's Next," and with a little planning, you will always have something coming next into fall.
I am not real thrilled with some of the Clematis growing along the south side fence. It should be sun, but it is not towards the back of the border because of the neighbor's foliage which I love so much in the spring. I am going to choose more carefully such as bloom time so that the vertical garden is going all season.
That's why gardening is such fun, there's never an end!