Horticulture Supervisor
Kyle N. Cheesborough
As fall relents to winter, and we experience the first truly cold nights, an interesting phenomenon occurs on a few of our native Missouri perennials. When nighttime temperatures drop well below freezing but the days remain just above that threshold, ice formations known as ‘frost flowers’ form along the stems of dittany (Cunila origanoides) and crownbeard (Verbesina virginica). These delicate, intricate, and dazzling structures form as the still-active roots of these two herbaceous plants continue to push water and nutrients into the stems, which rupture in the freezing temperatures as they go dormant. The rush of water and nutrients pushes through the cracks along the stem, immediately freezing as it seeps outward. As more sap is pushed from the roots, to the shoots, and out into the frozen air, ribbons of sparkling ice crystals form. 
If you catch them early in the day before the sun hits the paper-thin ice, frost flowers are a sight to behold, and one that even the most avid outdoor enthusiast can easily miss. Frost flowers form at the base of dittany and crownbeard, often covered by falling leaf debris. Find an area where these plants grow, and look for the frost flowers at the base of the above-ground stems.
Dittany is a low-growing perennial that prefers dry, slightly shady sights, such as a slope along the edge of a woodland, and occurs in central, south, and eastern Missouri. Crownbeard is more widespread, often earning the nickname ‘frostweed’, due to its ability to colonize a variety of sights. Look for the yellow, daisy-like blooms on crownbeard in the fall, atop slender, winged stems 1-2 feet high. Frost flowers only occur in the fall, and for only a few choice days where the nights fall below freezing and the days remain warm enough to keep the ground from freezing.
compiled by Cara L. Crocker
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