Many do not know that 4 o'clocks aren't annuals but are perennials in many southern zones. If You like a particular color, you can dig and store the tubers like a canna or dahlia. Or just get a leg up on next season without waiting for seeds to sprout. Planting a tuber speeds up blooming from 2 - 4 or more weeks.
I store most of my tubers each winter. Just check them periodically and lightly mist as they can dry out faster than a canna.