How can plants frost when the low temp is higher than freezing?

Answer 1

Dew point?

Answer 2

I don't think the gist of the question is how does the moisture necessary for frost occur, but RATHER, how does it become FROST, if the air temperature is above freezing.

Answer? UNLESS your plants are at the airport (where the "official" temperature seems to most often be recorded) AND existing at the exact height as that airport's thermometer then it's a pretty safe bet that the actual air temperature where you're seeing frost is in fact below freezing, EVEN if "officially" they say it didn't get below freezing.

Think of it this way ... when you watch the weather, they give temperatures "around the region." IF every temperature in the region were the same then there would be no reason to report 'em all. They would simply say, everyone is 36 degrees! What are they to do? They can't set up 10 of thousands of thermometers and record ALL the various air temperatures; so, they arbitrarily pick a spot and say, THIS is the official one!

Answer 3

Dew point and moisture play a big part in this.

The temperature at which the change of state occurs as the air is cooled is called the dew point temperature when the change of state occurs at a temperature above freezing or the frost point temperature when the change of state occurs at a temperature below freezing.

What determines the temperature of condensation or sublimation is the amount of moisture in the air, the greater the amount of water vapor, the higher the condensation temperature. During summer it is not uncommon to have a dew point of 70°F in the eastern United States. But in the cooler seasons the dew point can be below freezing, in which case it is called the frost point temperature.


Whether dew or frost will form is determined by two factors:

1. If the amount of moisture in the air causes the condensation temperature to be above or below freezing and
2. If the temperature will cool to the condensation temperature.