Hardiness Zones

• Rose of Sharon thrives in USDA hardiness zones 5 to 9. The coldest temperatures in zone 5 reach -20 to -10 degrees F. Help your Rose of Sharon survive winter by mulching it heavily in late autumn. During the most bitter cold snaps, or if heavy ice is expected overnight, cover your shrub with a sheet or a piece of burlap. Remove it during the day.
  
  

Potted Shrubs

• If your Rose of Sharon is in a container, do not bring it indoors for the winter. Protect its roots from freezing by placing it in an unheated garage, where temperatures do not go below 30 to 40 degrees F. The shrub is dormant during the winter, so it will not need sunlight. If you must leave it in the garden, wrap the pot with insulating material, such as Styrofoam, burlap or blankets.
  
  

Young Plants

• A young Rose of Sharon will not be as winter hardy as older, established shrubs. Overwinter young potted plants in a bed next to your house. The bed should be on the south or west side and protected from winter winds. Dig a large hole and place the entire container in the soil. Water the shrub well, then mulch heavily. The young plant will be protected during the cold weather and ready for moving to a permanent location in the spring.
  
  

Pruning

• Prune Rose of Sharon in late winter or early spring. Remove branches killed or weakened by cold weather. Then cut 1/3 of the shrub's branches to ground level each year. If you do not prune older parts of the plant regularly, its flowers will decrease in size, according to Virginia Cooperative Extension. Rose of Sharon produces flowers on each year's new growth, which means even plants that were damaged by cold weather should still bloom.