Chilling of air below the freezing point. Depending on the mode of occurrence, it is classified as:

1. Radiation frost: It occurs on nights with clear sky, produced by loss of heat by radiation. It occurs in plain and kills back young plants. Whenever ice crystals are formed on the ground and other objects near the surface, it is called ground frost or hoar frost.
2. Pool Frost: The accumulation to a considerable depth of heavy cold air flowing down into natural depression from adjoining areas. It occurs in hill and valley country
3. Advective frost: A frost produced by cold air brought from elsewhere

When an area is affected by frost more than other areas in the locality, it is referred to as frost pocket or frost hole or frost locality.

Frost Injuries

• Killing of young plants or their parts
• Death of plants due to damage to cells
• Injuries to the crowns of poles and saplings
• Frost cracks
• Formation of Canker

The species killed back by frost is called frost tender and the species which pose power to withstand frost without being damaged are called frost hardy.

Frost hardy: Khair, Sissoo, Khotesalla, Bayer, Mahuwa, etc
Moderately frost hardy: Banjhi, Karma, Simal, Satisal, Gamhari, Kimbu, etc.
Frost Tender : Babul, Nim, Teak, Arjun, Asna, etc

Factors affecting frost resistance

1. Internal Factors
   • Size of cell
   • Water content
   • Osmotic concentration
   • Permeability of water
   • Water-binding colloids
2. External Factors
   • Temperature
   • Light
   • Mineral nutrition

Hardening off

• It is the natural process by which plants become adopted to drought, cold or heat
• This term is also used for preparing seedlings in nursery, for planting out by gradually reducing watering, shade and/or shelter resulting in hardening off plant.