Four-o'clocks are a flowering plant native to South America. Four-o'clocks get their name because they flower in the late afternoon and bloom all night with the blooms fading in the morning. Many people plant four-o'clocks near doors or windows where the flower's pleasant aroma can be enjoyed. In USDA Horticultural Zones 7 to 11 (U.S. plant hardiness zones put forth by the USDA), four-o'clocks are perennial and may die to the ground in winter and return from the roots in the spring if protected with mulch. In colder climates, the potato-like tubers that make up the root system are dug up and stored over the winter.
Allow the four-o'clock plants to die to the ground. This is usually after the first freeze of the fall or winter season. Leave the dead plant material on top of the ground so you know the approximate location of the tubers you need to dig and store over the winter.
Dig the four-o'clock tubers from the ground by starting 12 inches from where the plants were growing and digging down as much as 18 inches. Gently work you way through the soil using a shovel or your hands protected with a pair of garden gloves. When you contact a tuber, gently pull it from the soil and put it aside. Young tubers look like odd shaped black carrots, older tubers are large and round and may weigh up to several pounds each. Do not wash the tubers after digging because you want them to be stay dry.
Place the tubers in a warm (65 to 80 F) location for up to three weeks until completely dry by laying the tubers on a table and turning every few days.
Prepare a cardboard box for winter storage by using a sharp knife to cut holes into the side of the box so the tubes have air circulation around them. Do not use plastic boxes or bags to store tubers because they hold moisture and cause the tubers to rot or mildew.
Cover the bottom of the cardboard box with two to three sheets of dry newspaper. Place one layer of tubers over the first layer of newspaper making sure the tubers do not touch. Add another layer of newspaper and another layer of tubers. Do not stack over three levels high in each box so air can circulate around the tubers. Cover the top layer of tubers with another layer of two to three sheets of dry newspaper. Store in a cool (40 to 65 F) and dry location until spring when the ground can be worked, and replant the tubers in a desired location.