Frost vs. Freeze

All gardeners know this is going to happen every year and still many are surprised. Frost versus freeze today on southern Gardening.

Not matter if we are enjoying moderate temperatures there will come a time that we will need to protect some of our landscape plants from freezing temperatures. And since no one reliably predicts the weather, now is the time to consider getting ready. Many calls I receive confuse frosts and freezes. While both are cold weather events, they are completely different. Frosts rely on the amount of water in the air. As air temperature drops low enough it becomes saturated and the excess water condenses as dew. An example of this is a cold glass of iced tea sweating on a hot summer day. Frosts will typically occur when the skies are clear with calm wind. Heat absorbed by the soil and plants during the day is transferred to the air at night. An inversion layer forms where surface temperatures drop below freezing and warmer above. If the surface temperature and dew point is below freezing, ice crystals will form on the cool surfaces. Sometimes the air is too dry for ice crystals to form, but a frost event has still occurred. And frost can occur when the air temperature is above 32 degrees. A freeze occurs when a mass of cold air moves into Mississippi, many times with windy and cloudy conditions. This is the typical scenario and is a very different than a frost.

Plant damage is dependent on how low the temperature drops and length of time at that low temperature. A hard freeze occurs at temperatures below 28 degrees.

I’m horticulturist Gary Bachman for Southern Gardening.