Sangeetha Pulapaka
1

Frost is frozen water that has condensed from water vapor in the air. For frost to occur, surface temperatures must be below freezing (otherwise you would see dew, not frost). Frost forms on plants when they are colder than the dew-point temperature of the surrounding air.

                                              

Frost is rated by the severity of the frost layer. The higher the dew-point temperature, the more water is in the air, and the higher the rate of frost accumulation. Light frost will damage smaller plants more than larger, established plants. Severe frost will damage and even kill most plants that are not dormant.

Classification of freeze temperature is usually based on its effect on plants. A light freeze is 29°F to 32°F — tender plants are killed with little destructive effect on other vegetation. Moderate freeze is 25°F to 28°F — widely destructive to most vegetation, with heavy damage to fruit blossoms and tender and semi-hardy plants. Severe freeze is 24°F and colder — damage to most plants.

The lower the temperature, the longer the exposure, and the faster the temperature drops, the greater the damage to the plant.Protect plants by:

  • covering
  • moving 
  • applying water or heat
  • increasing air circulation


Since you asked about ice let us talk about applying water to preserve plants.  A very low rate of application of water through irrigation can be effective in preventing freeze damage through the release of heat during cooling and freezing. Protection from freezing temperatures as low as -60C have been reported for low growing berry and vine crops, when 1.5 to 2.5 mm per hour of water was applied.Sprinkling of the crop should begin with the onset of freezing conditions and a film of water continuously maintained until temperatures have risen above the freezing level (0 C). If sprinkling is discontinued prematurely, heat will be drawn from leaves to melt the ice and freeze damage may result. This method creates another problem if the frost lasts too long, because the plants must be able to support the added weight of ice that builds up on the leaves and branches. A forecast of the duration that temperatures are expected to remain below freezing is very useful when using this method. In spite of the problems, this method has proven effective for low growing crops such as strawberries, tomatoes, beans, cucumbers, peppers and squash as well as vine crops and tree fruits. It is important to recognize that this method only prevents the temperature of the protected plant from falling below the freezing point. It does not warm the plant parts nor does it raise the air temperature appreciably. Moreover, sprinklers need to provide constant, uniform coverage. There is controversy over the use of irrigation as a protection method prior to frost occurrence. The added moisture has the beneficial effects of increasing the capacity of the soil to store heat and improving conduction of heat to the surface. Nevertheless, heating of the soil during day time is reduced because increased evaporation uses up heat energy. Moisture may also change the critical temperature which is needed to cause freeze damage to a crop. Since there are counteracting factors, a general recommendation cannot be made.