What Causes Frost?
Frost or hoarfrost causes or occurs when air temperatures of the surface dip below freezing and ice crystals form on plant leaves, injuring, and sometimes killing, tender plants.
But what causes pretty, leaf-like patterns to form, as opposed to just a sheet of frost?
Frost usually forms when a surface cools through loss of infrared radiation to a temperature which is colder than the dew point of the air next to the surface, and the temperature of that surface is below freezing (32 deg F, or 0 deg. C). The source of this moisture is water vapor contained in the air.
Frost is moisture from the air that has collected as tiny crystals of ice on leaves and blades of grass. Frost forms in much the same way as dew.
During the daytime, the sun warms the earth. As soon as the sun sets, the earth and the air surrounding it start to cool. When air cools, it begins to give up some of its moisture.
When the air temperature is above freezing, the moisture in the air changes into drops of water, which collect as dew on solid objects. But when the night is very cold, the moisture forms ice crystals, or frost, instead of dew.
Frost on its way? If a frost is predicted, cover your plants, both to retain as much soil heat and moisture as possible and to protect them against strong winds, which can hasten drying and cooling. You can use newspapers, baskets, tarps, straw, and other materials to cover your plants. Cover the whole plant before sunset to trap any remaining heat. Be sure to anchor lightweight coverings to prevent them from blowing away.
Keep the soil moist by watering your plants the day a frost is predicted. Commercial fruit and vegetable growers leave sprinklers on all night to cover plants with water. As the water freezes, it releases heat, protecting the plants, even though they’re covered by ice. To prevent damage, the sprinklers need to run continuously as long as temperatures remain below freezing.