Rose of Sharon hibiscus (Hibiscus syriacus) is safe to keep in a container outdoors in NYC throughout the winter and will grow in our gardens in USDA zones 5 to 8. In severely cold weather, pull a potted plant closer to the home to protect it from wind, particularly if the plant is on a terrace above ground level where it will experience additional stress. The roots of plants in containers have greater exposure to cold than plants in the ground and they are more vulnerable to winds when grown in an elevated location. Take care that your plant is the winter hardy Hibiscus syriacus and not a tropical hibiscus plant before leaving it outdoors for the winter.

This shrub is slow to leaf out in spring and it is easiest to cut back when the woody structure is leafless and  visible. In the early spring, this plant can be pruned to contain its size, restore vigor and to promote more profuse flowering. It will produce new growth in the current year and flower on that growth in the summer. You can cut it back hard into thick branches to maintain a slightly smaller size that suits your space and promote flowering.  You can also cut stems back so that two to three buds remain on each for fewer but larger flowers. 

Courtesy of NYBG Plant Information Service