Chilling Injury, Frost and Freeze Injury: What's the Difference?
Chilling injury is damage to plant parts caused by temperatures above the freezing point (32°F, 0°C). Plants of tropical or subtropical origin are most susceptible. Chilling-injured leaves may become purple or reddish and in some cases wilt. Both flowers and fruit of sensitive species can be injured.
Frost and Freeze Injury
Frost injury and freeze injury are closely related. Frost damage occurs during a radiation freeze; freeze damage occurs during an advection freeze. In both cases, ice crystals form in plant tissues, dehydrating cells and disrupting membranes.
- Advective freezes occur when an air mass with a temperature below freezing moves into an area and displaces warmer air, causing the temperatures of plants to become low enough for ice crystals to form within their tissues.
- Radiation freezes occur on clear, calm nights when plants radiate (lose) more heat into the atmosphere than they receive. This creates a temperature inversion in which cold air close to the ground is trapped by warmer air above it (the temperature of the air increases with altitude). When the air temperature at plant level is near or below freezing, the temperature of the plants is likely to be colder than the temperature of the air.
If plants become sufficiently cold, the water in them freezes and cells are damaged. The frost that appears on plants is simply ice crystals that form on the plant surface, equivalent of dew forming at temperatures above freezing. The frost itself does not damage plants; plants are damaged by ice crystals that form within their tissues.
Additional information can be found on pages 133 to 138 in Abiotic Disorders of Landscape Plants: a Diagnostic Guide. (UC Publication 3420)