The amount and timing of pruning for your hibiscus depends on what kind of hibiscus it is, and where you live. Tropical hibiscus (Hibiscus rosa-sinensis) is hardy only in Zones 9-11. If winter temperatures dipped below about 20°F, and you have a tropical hibiscus, the plant is likely dead. However, you could wait until spring to see if anything sprouts. Sometimes the stems die back, but new shoots arise from the base of the plant. Wait until the weather warms in spring, then prune back to where new, healthy growth is emerging. Hardy hibiscus (H. moscheutos) is root-hardy in Zones 4-9. Plants die back completely and can be cut back to within a couple of inches of the ground in late fall or early spring. New shoots will emerge from the crown of the plant in late spring after the weather has warmed up.