Frost Flowers

Frost Flowers
Glen Conner, Former State Climatologist for Kentucky

Frost flowers are thin layers (perhaps credit card thickness) of ice that are extruded through slits from the stems of white or yellow wingstem plants, among others. Their formation requires freezing air temperature, soil that is moist or wet but not frozen, and a plant's stem that has not been previously frozen. (Practically speaking, a once per year event, although not all individuals produce frost flowers on the first day of good conditions). The water in the plant's stem is drawn upward by capillary action from the ground. It expands as it freezes and splits the stem vertically and freezes on contact with the air. As more water is drawn from ground through the split, it extrudes a paper thin ice layer further from the stem. The length of the split determines if the frost flower is a narrow or wide ribbon of ice. It curls unpredictably as it is extruded, perhaps from unequal friction along the sides of the split, to form "petals". These flowers, no two of which are alike, are fragile and last only until they sublimate or melt.

To find them, look for tall weeds, especially in locations that are seldom mowed. They seem to like the same habitat as purple ironweed, blackberries, and wingstems.

Here are some spectacular frost flowers that were photographed on the morning of November 14, 2012 in southern Kentucky. The low that morning was 27°, with a temperature of 31° at the time the pictures were taken. The flowers formed on yellow wingstems. Click on an image to see a larger version.

The following images were taken on the morning of November 18, 2011 in southern Kentucky. Click on an image to see a larger version.

These frost flowers were spotted by Amy Tichenor Smith on November 15, 2022:

The images below are courtesy Phil Schaad in Henry County on November 5, 2021:

Hoar Frost
Dr. Mark Huntsman, Scottsville, KY

"Hoar" is an old word (variations have been found back to the 1200s) that can mean "grey" or "greyish-white". It comes from an older German word that meant "venerable", especially in reference to an older person. (OED)