I saw this posted on Facebook this morning and thought it was really interesting!

Here is an excerpt from the Manhattan Community Garden Newsletter, written by Dr. Chuck Marr:

“You have often heard these 2 terms used interchangeably. However, for horticultural purposes there is something of a difference. This is forever etched in my brain since a former professor quizzed me about this in one of my final oral examinations. I think he wanted to demonstrate that he knew more about this topic than I did (and he won). A frost refers to ice crystals that form on various surfaces. This traditionally happens when a ‘radiational freeze’ occurs. As the night goes on, heat is lost from near the ground. Some plant tissues can be frozen at the outside edges while others areas inside the plant can be spared when heat gets trapped. It is easy to protect from this type of damage with some kind of insulating cover for 2-5 degrees below the freezing point. These radiational freezes often are difficult to predict and there will be some variation in locations from heat emitted from surrounding structures and cold air moving to low lying areas. A freeze usually refers to an ‘advective freeze’ when a large cold air mass moves into the area and freezing plant tissues happens. Old-timers often called this a ‘black freeze’ since there my not be any white colored frost but a lot of blackened plant tissue. In this case, there is generally a freezing of tissues equally all over the plant. These are harder to protect by covering although some protection may be gained. Forecasters can more accurately predict and estimate temperatures from this type of freeze so the temperatures are usually close to what is predicted everywhere. So, when you hear the weather forecast predicting a ‘frost warning’ or a ‘freeze warning’ this is what they are talking about. Both can damage plants but a frost is a lot easier to deal with than a freeze.”