Frost on blades of grass. Woodcut artwork of blades of grass covered by an early morning frost. Frost forms when the ground temperature falls to below the freezing point of water. Water vapour in the air freezes on the ground, and other surfaces, such as plants. This forms a covering of ice crystals that is called frost. Plants that grow in temperate regions of the world are adapted to survive brief periods of frost, but can be killed by particularly severe or extended frosts.