Minimum Temperatures

• Temperatures below 28 to 30 degrees Fahrenheit kill all exposed parts of the hibiscus plant. Frost will invariably kill the hibiscus down to the ground. Large plants may recover from frost by regrowing from the roots and may even flower later on in the same year. Protect hibiscus plants by draping them with a frost cloth if frost if forecast. Water them thoroughly, as dehydrated plants are vulnerable to cold damage.
  
  

Growing Temperatures

• Hibiscus plants will not grow new leaves or produce flower buds at temperatures below 55 degrees Fahrenheit. They are also intolerant of large temperature fluctuations, which cause bud drop. Grow hibiscus plants in a sheltered location away from cold winds. They need at least half a day of sunshine every day to thrive. Keep indoor plants out of drafts and away from heaters and air-conditioning units.
  
  

Optimal Temperatures

• Hibiscus plants thrive between 65 and 75 degrees Fahrenheit but growth is inhibited by higher temperatures, especially if they are grown in full sun.
  
  

Protecting Hibiscus Plants

• Drape outdoor plants with a frost cloth if frost is forecast and water them well. Dehydrated plants are more vulnerable to cold and frost damage. Mulch the soil around a cold-damaged outdoor plant to keep the roots warm and encourage regrowth. Move container-grown plants indoors before temperatures drop below 55 degrees Fahrenheit. Keep indoor plants from touching windows during the winter as cold glass scorches leaves. Treat hibiscuses as annual plants in areas with regular frosts.