Hibiscus flowers of differing species and varieties thrive in United States Department of Agriculture Plant Hardiness Zones 4 through 11. Zone 4 is the coldest zone where hibiscus are found. Winter temperatures in this zone are known to drop to minus 20 F. Only the hardiest perennial hibiscus are able to withstand these severe temperatures. Kopper King is a perennial hibiscus that, in this growth zone, dies back to the ground each winter but reemerges to bloom again in spring. Other cool weather hibiscus include common rose mallow (Hibiscus moscheutos) and Rose of Sharon (H. syriacus).
Hot Climate Hibiscus
Hibiscus rosa-sinensis, also called Rose of China, Hawaiian hibiscus or Chinese hibiscus, is grown outdoors in warm climates such as those found in zones 8 through 11. Zone 8 and 9 cover a large swath of the Southeast as well as the West Coast shoreline. Zone 10 is found in southern Texas and Florida. Hibiscus in these areas grow well in containers or in gardens where their fragrant blooms display from spring until the weather cools in fall.
Over 200 species of hibiscus exist and most thrive indoors. When growing hibiscus indoors it is important to maintain a consistent temperature. Cool drafts, warm electrical appliances and proximity to heaters or air conditioners can damage hibiscus. Maintain a temperature range of 55 to 75 degrees Fahrenheit. The upper range of temperatures encourages optimal growth. When hibiscus experience bud drop, the main culprits are cold, limited light, excessive heat or irrigation extremes. Hibiscus prefer slightly moist, well-fertilized soil.
Hibiscus are tropical and subtropical plants that are prone to diseases brought on by humidity and warmth. Whether grown indoors or out, check your plants for aphids, white flies, spider mites and Japanese beetles. Removing debris lessens the chance that insects will infect your hibiscus. Fungi is also a problem and causes leaf spot. Southern stem blight is another fungal disease. Ensure that mulch does not touch the plant's stem. Keep plants well maintained and avoid overcrowding. Divide hibiscus in spring, as they will not tolerate fall division.