How Much Cold Can a Hibiscus Stand?
The hibiscus grows as an outdoor shrub in many tropical locations, delighting gardeners year-round with a display of colorful flowers. But as cold nights begin to arrive, the potential for frost can mean trouble for the hibiscus. In northern locations, the plant must be transferred indoors for protection.
A genus of plants that includes more than 200 species, the hibiscus is believed to have originated in China and may have been a hybrid that combined two or more species from an area around the Indian Ocean -- specifically, Madagascar and the Seychelles Islands. As a result, the plant prefers warm, humid conditions. The tropical hibiscus, Hibiscus rosa-sinensis, possesses a showy flower in a wide range of vibrant colors, and the plant itself often grows as tall as 15 feet.
The hibiscus is hardy through USDA hardiness zones 9 and 10 -- an area that includes south Florida and the extreme southern tip of Texas, in addition to Hawaii. Frost damage is very common and some cultivars -- even in these hardiness zones -- are damaged or killed when temperatures drop below 30 degrees Fahrenheit. While the plant can be grown outdoors during the summer months in northern climates, it must be brought indoors before the first possibility of frost.
When the hibiscus grows inside, it still requires relatively warm conditions. Indoor, daytime temperatures should never fall below 55 degrees Fahrenheit, with 65 degrees to 75 degrees Fahrenheit being best for ideal winter growth, advises the University of Minnesota Extension service. Failure to adhere to these guidelines could result in flower buds dropping away or simply refusing to grow. The hibiscus does not appreciate dramatic fluctuations in temperature or humidity, so avoid placing it in drafty areas or near heating sources.
A hibiscus can tolerate moderate freezing temperatures, and knowledgeable gardeners will watch the plant for signs of how to best help it. If a hibiscus is damaged by frost, the injury may not appear immediately. Hibiscus blooms on new growth, so allow the freeze-damaged hibiscus approximately three to four months to grow new wood so you can tell what parts of the plant require pruning, suggests a 2007 article in the "Houston Chronicle." Damaged sections should be cut back to the green wood.