Our Window on Nature

. . . exploring the world around us

Finding Frost Flowers

Filed under: Plants — Lowell Christie -- November 24, 2015 @ 12:57 pm

Frost_flower_closeupWe intentionally schedule many of our activities to the rapidly passing dates of the calendar. Early spring is for chasing birds, but it soon competes with photographing wildflowers. Early summer and we head for the beach (or the shore if we’re in the east.) Early fall finds us marveling at the changing colors, watching as leaves drop from the deciduous trees. And this year early winter has us looking for frost flowers.

No, not the artwork Jack Frost leaves on a windowpane after a cold winter night. These frost flowers are associated with the plant world, although they appear long after everyone expects the flowering season to be over. Frost flowers materialize from plants that appear to be dead or dying, but they rival the beauty of springtime blossoms.

If you haven’t heard of frost flowers, neither had we until a few months ago. Always intrigued by old nature books, we stumbled upon mention of the frost flower in a 1891 book called Sharp Eyes by Wm. Hamilton Gibson. He spoke of “Flowers of three kinds on a common plant, only one of which is generally seen: a showy flower with petals, a flower with no petals, and a flower of ice crystal prettier than either.”

A flower of ice crystal sounds too good to pass up, but Gibson only gives us a hint of this amazing “flower” that few have ever seen. The plant of which he writes is Helianthemum canadense, whose common name is frostweed. Blooming in the southeast during the summer, it has a brilliant yellow flower with five wedge-shaped petals. Later in the year it has many small, inconspicuous flowers without petals. And if the conditions are right, when the first frosts appear, it may produce a flower of ice – the frost flower.

From what looks like a dead plant (it’s actually a perennial), a cold snap may cause the stem to split, allowing a combination of water and sap to extrude. Depending upon the difference between the ground and air temperature, this liquid may freeze into fantastic shapes, forming winding ribbons, spirals, or sometimes mimicking the actual shapes of flowers. Here’s how Gibson describes it.

“It is a flower of ice crystal of purest white which shoots from the stem, bursting the bark asunder, and fashioned into all sorts of whimsical feathery curls and flanges and ridges. It is often quite small, but sometimes attains three inches in height and an inch or more in width. It is said to be a crystallization of the sap of the plant, but the size of the crystal is often out of all proportion to the possible amount of sap within the stem, and suggests the possibility that the stem may draw extra moisture from the soil for this special occasion.”

Exactly how this process occurs is only partially understood over a century later. The attractive structure is made of ice, and it exits the plant’s stem through a rupture. But the end result makes it obvious that the material making up the “flower” flows through the opening. We don’t normally think of ice as flowing. An understanding of the conditions under which frost flowers appear gives a hint of what may be happening.

The ground can’t be frozen, since that would prevent the movement of water. But the air must be very cold – cold enough to make water freeze upon contact. Since water expands while freezing, the expansion may either rupture the exterior of the stem, or it may force water through an old crack. Some think that the water inside the stem may already be supercooled, a condition where water can be below the freezing point while remaining liquid.

In any event, when the water hits the air it immediately forms ice. Additional water exiting the stem pushes this ice away from the opening, and in its turn freezes. The resulting shape depends upon the contour of the rupture; for example, a long thin opening would create a wide ribbon of ice.

Yet to be discovered is why so few plant species create frost flowers. In addition to frostweed, four other plants are known to produce these icy ornaments: white crownbeard, yellow ironweed, wild oregano, and dittany. Unfortunately for many of us, all five of these species are native only to states from Texas to the east coast.

Dr. James R. Carter, who has studied frost flowers and related phenomenon, believes there must be at least a dozen species that produce these ice sculptures – it’s just that nobody has noticed them yet. There’s an obvious reason.

Frost flowers suddenly appear overnight, but are so fragile that a touch of the sun will quickly melt them. Only frost flowers appearing in the shade are likely to survive very long after sunrise. So, how many walks do you take at or before sunrise on an extremely cold morning? Those who actually find a frost flower are usually actively looking for one.

If you live in or visit the southeast and decide to look for frost flowers, the easiest way is to locate the plants that produce them. Since the plants may be only dry stems, that can be difficult. But if you find a frost flower mark the spot, because the same plant may produce another flower at the next frost. An early botanical book by a Professor Eaton says “In November and December of 1816 I saw hundreds of these plants sending out broad, thin, curved ice crystals, about an inch in breadth from near the roots. These were melted away by day, and renewed every morning for more than twenty-five days in succession.”

For those of us not living in the southeast, there are other possibilities. The creation of a frost flower is just a physical process involving water, temperature, and pressure. Something similar may happen on a cold frosty morning to broken-off conifer branches lying on damp ground. It usually takes the shape of fine, hairlike structures called icebeard as water is forced out of pores in the wood. Not quite as striking as its eastern relative, but while we’re searching perhaps we’ll find one of those unknown plants that really can create frost flowers. It’s certainly worth a look.


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