Damage

• Frost causes the majority of cold-weather damage to citrus trees. The freezing temperatures kill both leaves and fruit.
  
  

Limit

• Most citrus trees and their fruit will sustain damage when the temperature drops below 28 degrees Fahrenheit for longer than four hours at a time.
  
  

Cold Hardiness

• Slightly warmer temperatures will affect each type of citrus tree differently. Lime and lemon trees are the most susceptible to cold, and mandarins are usually the least susceptible. Oranges and grapefruit are in the middle.
  
  

Radiative vs. Advective

• A radiative frost comes during calm weather when the heat is lost by radiation. An advective frost is when the heat is lost because of a blowing cold air mass. Given the same temperature, advective frosts cause more damage to citrus trees.
  
  

Tree Stress

• Citrus trees that are stressed because of drought or disease are more susceptible to cold damage, according to the University of Florida website.
  
  

Proline

• Proline is an amino acid in citrus tissues associated with cold hardiness. Proline increases in citrus trees as the temperature gets colder, which is why a sudden drop in temperature is harder on citrus trees than a gradual one, because the proline does not have a chance to build up.