When I had a roofdeck, I would plant morning glories in every container and by the end of the summer, their huge blue flowers would cover every rail (and take a few hours to cut down late fall!). The best morning glory for quantity of blooms is Heavenly Blue. If planted in the ground, they can become invasive so must be managed – ie. Keep your eyes peeled and pull up extras in the spring.
My favorite combinations for a yard include blue asters, Sedum Autumn Joy and Montauk Daisies planted together. You might find Montauk Daisies at the local Whole Foods sold as potted plants – just throw them in the ground for a fairly large shrub for next year! These are very hardy, very florific white daisies in the late fall when nothing else is in bloom. Trim these down some in fall but primarily in early spring (before June). These will also easily root if a branch is touching the soil so are easily proliferated. Note that asters are also very easy to just shovel in half to divide. I was so glad I had divided my favorite before it was infested and killed by AZALEA LACE BUGS. Lesson there is to take quick action when you see anything starting to falter – inspect and deal with it.
Caution: I would not plant a white aster, which is lovely for a few years, and then will invade your entire bed and spread around your yard. Do not do it!
Mums are great and are perennials – I have heard if you buy the ones distributed in the fall and plant them early enough, they might come back. I haven’t had much luck with that but have beautiful perennial ones I have ordered from catalogs and planted in the spring. Mums will also spread so don’t hesitate to pull out strays you see coming up. They get to be 3-4’ tall and should be staked late August. Nothing beats a few mums bought at the local nursery to spruce up a worn bed – I will plant them in sets of 3 in my main perennial beds.