Low Water Flow

• Near or subfreezing temperatures have a number of affects on tropical hibiscus plants. The cold weather slows or stops the flow of water through the soil and through the roots and veins of the plants, which is the source of most of the cold-weather damage. Lack of water flow leads to wilting and possible loss of leaves and flower petals. In a best-case scenario, a temporary interruption in water flow will only cause smaller blooms or slightly stunted growth for the year, which can be made up in warmer weather.
  
  

Wind and Ground Damage

• Freezing temperatures tend to also bring with them harsh winds, which can easily blow young blooms off of the hibiscus plant. Extremely strong winds can break the stems of the flower altogether. Snow on the ground will cause the slowdown of water to last even longer as the soil itself freezes, leaving your plants more susceptible to the wilting and dying off that can come from cold weather.
  
  

Ideal Growing Temperatures

• The ideal temperatures for growing hibiscus plants range between 65 and 85 degrees Fahrenheit. While they are tropical plants, hibiscus can be harmed by temperatures that are too high as well. Full sun exposure with temperatures exceeding 90 degrees Fahrenheit can cause drought-like effect similar to those caused by freezing temperatures, including smaller flowers, shorter stems and increased risk of leaf and bloom loss.
  
  

Cold Water Solutions

• The key to protecting your hibiscus from cold weather is in the watering. If you know that freezing temperatures are approaching, water your hibiscus with room temperature or lukewarm water at least a day ahead of time. This will give the roots enough time to absorb the water before the cold sets in, and if it is only a short cold snap, the hibiscus may escape unharmed. If you are trying to see hibiscus through a long stretch of cold, water them with warm water every other day; the warm water will seep through the cold soil more easily and get to the plant's roots.
  
  

Protective Insulation

• If high winds and snow are the trouble, consider covering your hibiscus with tarp or cheesecloth to allow sunlight through but insulate the ground to retain heat. This can also be accomplished with a 3- to 4-inch layer of organic mulch around the base of the plants, which will help the soil maintain moisture and also slow the loss of heat from the soil. The mulch also provides a layer of protection between the soil and any snowfall or frost.