February 20, 2021
Just before the extreme winter temperatures fell upon us last week, my husband called me quickly to our backyard. He was concerned about the unusual ice formations surrounding the stems of our Frostweed plant. Had he forgotten to turn off the sprinkler system or was our plant in distress?
Most years, after those beautiful fall blooms have faded and the plant turns brown, we would already have cut it down to ground level. Seems this year, it was overlooked. As we carefully touched the somewhat intriguing white substance, it was evident that the plant stems were covered in frost.
After doing a little online research, I discovered the reason for the plants name. Frostweed, Verbesina virginica is a Texas native biennial that ranges in height from 3 to 6 feet. Our plant has easily reached the six-foot mark. It blooms in late summer and continues blooming until frost. The plant was named Frostweed because of this unique characteristic of producing intricate ice formations from its stems. Only a few species of plants are capable of producing these ice creations, more generically referred to as “frost flowers.”
As early as 1833 John Herschel, son of the famed astronomer William Herschel, who discovered the planet Uranus in the 18th century, made an interesting observation. In a letter printed in Philosophical Magazine he describes going for an early morning walk several winters before noticing “a remarkable deposition of ice around the decaying stems of vegetables.” A few days later, he found a similar strange ice formation, this one seeming to emanate in a kind of riband-or frill-shaped wavy excrescence.”
Herschel’s letter is one of the earliest recorded observations of the phenomenon of “frost flowers” (sometimes called ice flowers or ice ribbons). However, he could only hypothesize about the cause of these formations. Not able to explain, he concluded that “It is for botanists to decide.”
Scientists are unsure why only a few plants in nature produce crystal ice patterns into ribbons or clusters that resemble flowers, and why only certain types of plants are affected. One theory is that frost flowers develop when air temperatures are freezing but the ground temperature is warm enough for the plant’s root system to be active and the air temperature is cold enough to freeze the upward flowing plant juices. Perhaps, as the moisture in the plant freezes, the ice crystals push out through the stem. They may emerge from a small slit to form thin ribbonlike strands. Or they may split open a whole section of the stem and push out in a thin, curling sheet.
Another theory is that the stems rupture and crack in just the right way so sap oozing out forms into wide ribbons that freeze into the ice patterns.
As you can see from the photographs, our frostweed plant seems to have formed frost crystals resembling spun cotton candy. Notice, also, that the formations are mainly around the base of the plant descending upwards for about two feet.
Whatever the true scientific reason for this phenomenon of nature, we now know that next fall when blooms are spent, frostweed will remain in our garden throughout the winter months. Even our 5-year-old granddaughter, Sadie, was so intrigued with the crystals that she couldn’t resist gathering up a handful. Oh, the joy of experiencing childlike wonders found only in nature.
Pictures by Linda Alexander and Beverly Allen
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