Like summer dew, frost appears on clear windless nights as the air cools and can’t hold as much moisture as it did during daylight hours. In summer and early fall, this excess moisture condenses on the surfaces of weeds, spider webs, metal tools, and other exposed objects. But when the temperature falls below 32-degrees the same vapor crystallizes, forming frost.
Through a process known as deposition. , the vapor does not turn first into water and then freeze. Instead, it changes directly from the gaseous state into a crystalline form. As more and more vapor freezes, delicate featherlike patterns of “window frost” (also called “fern frost”) are formed when a windowpane is exposed to very cold air on the outside and moderately moist air on the inside. The glass surface influences the shape of crystals, so imperfections, scratches, or dust can modify the way ice nucleates.
Looking like spun glass or cotton candy, “frost flowers” (also called “crystallofolia”) are very rare and very beautiful. They occur when there are freezing weather conditions when the ground is not already frozen. The water contained in a plant expands, creating cracks along the stem. Via capillary action, the water seeps out of the cracks and freezes on contact with the air, creating an ephemeral structure that closely resembles a flower. I have most often observed them exuded from the stems of common dittany (Cunila organides), a plant that’s common in the piedmont but uncommon in WNC.
Winter can be grim, of course, but it is in many regards the sweetest season of all. It’s the time when we see most clearly and feel most keenly. As Coleridge implies, it’s the season that’s ushered in via “the secret ministry of frost.”
“Therefore all seasons shall be sweet to thee,
Whether the season clothe the general earth
With greenness, or the redbird sit and sing
Betwixt the tufts of snow on the bare branch
Of mossy apple tree, while the nigh thatch
Smokes in the sun-thaw; whether the eave-drops fall
Heard only in the trances of the blast,
Or if the secret ministry of frost
Shall hang them up in silent icicles,
Quietly shining to the quiet moon.”
— S.T. Coleridge, Frost at Midnight