Hibiscus plants are popular for their large, striking blooms, but their cold tolerance differs greatly depending on the variety. Whether you can leave your hibiscus outdoors for the winter depends entirely on if it is a tropical or a hardy type, and what your local climate is like. The United States Department of Agriculture (USDA) Hardiness Zone map dictates the average minimum winter temperatures a plant can survive. Understanding this distinction is crucial for ensuring your plant survives the cold season.
The Crucial Difference Between Tropical and Hardy Varieties
The two most common groups of hibiscus require vastly different winter care. Tropical hibiscus, primarily Hibiscus rosa-sinensis, are native to warm climates and cannot tolerate frost. These evergreen shrubs thrive in USDA Zones 9 through 11, where temperatures rarely drop below freezing. If exposed to a hard frost, the tropical variety will not survive outdoors.
Hardy hibiscus, including species like Hibiscus moscheutos (Rose Mallow) and Hibiscus syriacus (Rose of Sharon), are built for cold. These herbaceous perennials die back completely to the ground after a hard frost, surviving the winter via their roots. Hardy types thrive in USDA Zones 4 through 9, tolerating temperatures as low as -30°F (-34°C). These varieties require winter dormancy and will not perform well if kept active year-round.
Protecting Hardy Hibiscus Left Outdoors
Hardy hibiscus, while cold-tolerant, benefit from preparation before deep freezes arrive. This ensures the root crown remains protected from extreme cold and freeze-thaw cycles. In late fall, after the foliage has died back, cut the old stems down to about 6 to 8 inches above the soil line. Leaving a short stub helps mark the plant’s location, as they are notably late to emerge in the spring.
Apply a thick layer of organic mulch around the plant’s base, extending past the crown. This layer should be 4 to 8 inches deep, using materials like shredded leaves, straw, or wood chips. The mulch acts as an insulator, regulating soil temperature and preventing the roots from being heaved out of the ground by alternating freezes and thaws. If hardy hibiscus is grown in a container, the pot should be insulated or moved to a sheltered spot, such as an unheated garage, to prevent the roots from freezing solid.
Overwintering Tropical Hibiscus Indoors
If you live outside of USDA Zones 9 to 11, bring your tropical hibiscus indoors before nighttime temperatures consistently drop below 50°F. This temperature drop can cause leaf loss. The plant must come inside well before the first anticipated frost, as freezing temperatures are lethal. Before moving the plant, prune the branches back by up to one-third of their length to manage the size and shape for its indoor location.
Inspect and treat the plant for pests to prevent infestations from spreading to other houseplants. Pests like spider mites, aphids, and whiteflies often hide on the undersides of leaves. Spraying the entire plant with a strong stream of water or a horticultural oil, like neem oil, will help eradicate them before the move indoors. Once inside, the plant needs a location that provides bright light, ideally near a south or southwest-facing window, for at least six hours daily.
If a bright, warm spot is unavailable, force the plant into dormancy by placing it in a cool, dark location where temperatures remain between 50°F and 60°F. Watering must be reduced during the winter months, whether the plant is active or dormant. For actively growing plants, only water when the top inch of soil feels dry. Water dormant plants sparingly, just enough to keep the roots from completely drying out. Withhold fertilizer until new growth resumes in late winter or early spring.
Spring Transition and Damage Assessment
Once the threat of frost has passed and outdoor temperatures are consistently above 50°F, it is safe to transition your hibiscus back outside. Tropical varieties moved indoors must be “hardened off” to acclimate them to intense UV light, stronger winds, and temperature fluctuations. This involves gradually exposing the plant to outdoor conditions, starting with a few hours in a shady spot. Slowly increase the duration and sunlight exposure over one to two weeks. Moving the plant directly into full sun without this step can result in severe leaf burn and shock.
Patience is required for hardy hibiscus left outside, as they are often one of the last plants to break dormancy. New growth emerges from the roots, often not appearing until late spring or early summer. If old stems were left in place, cut them back completely to the ground once new shoots begin to emerge. If any stems appear healthy but fail to sprout leaves, prune them back to a healthy node or remove them entirely to encourage robust new growth from the crown.