One was problem was its tendency to stop flowering at high temperatures. Breeders were also trying for more regular flowering and growth habits of some varieties. Both problems seemed to have improved, if not solved. With the new cultivars, flowering may slow during the heat of summer but shouldn't completely stop and growth and flowers are said to be more uniform. One characteristic gardeners will have to live with for awhile is the flower's habit of closing at dusk.
Breeders are still hard at work on that one.
Among the recent introductions is Passion Mix, a dwarf that is available as seed. It has flowers in purple, rose, and white. In 1999 it was chosen as an All-American Selection. According to Thompson and Morgan, it's an easy seed to start. Care is very straight-forward.