The lovely four-o'clock flowers, with their trumpet blossoms that wait to open until late in the day, add distinct charm and interest to sunny flower gardens. Four-o'clocks are hardy to USDA Zones 7B through 11, and gardeners living in these regions can grow four-o'clocks as perennial plants. Gardeners in colder regions must remove the tubers from the soil in the autumn and save them over the winter for planting again the following spring. When you care for four-o'clock flowers carefully at the end of the season, they should give you years of prolific growth.
Dig up the four-o'clock tubers in mid-autumn when the foliage begins to wilt and die back. Use the trowel to dig through the soil to find the long, slender tubers growing vertically into the soil. Remove them carefully, digging them up without severing them.
Clip off any remaining foliage from the tops of the tubers with the pruning shears. Discard the foliage.
Line the bottom of a plastic bin with three to four layers of newspaper.
Place the four-o'clock tubers onto the newspaper, spreading them out into a single layer without allowing the tubers to touch each other.
Cover the first layer with newspaper and add additional layers, if necessary. Separate each layer with newspaper.
Place the plastic bin in a cool and dry location. Temperatures between 40 and 65 F are ideal for four-o'clock storage. Store the four-o'clocks in the uncovered plastic bin until the soil warms the following spring.