Penta plants are 3- to 4-foot shrubs that are evergreen in some warmer climates of the United States, such as southern Florida. The penta can be damaged by frost in other areas, so it needs to be cut back before winter sets in. Pentas can also be cut back to control their sprawling size, or if they become too leggy or top heavy. Pruned pentas will resprout in spring when the weather warms, and will produce white, pink or red flowers on the new growth.
Wait for the blooming season to end. Deadhead the plant during the blooming season by picking off faded blooms to encourage further flower production until it is too cold for any more blooms to appear.
Cut the penta back to 12 inches above soil level with sharp pruning shears. Do this in the late fall or early winter. Compost or discard the plant material you have removed.
Apply a 3- to 4-inch layer of mulch around the base of the plant to keep it from heaving out of the ground during winter's frost/thaw cycle. You can also dig up the cut back penta, pot it and store it in a garage over winter.
Repeat the cutting back every winter. This prevents the plants from getting leggy, controls the size and prevents frost damage to the foliage.