Frostweed

Jan 29, 2016 - 3:00 pm

Frostweed Winter's Magic by William Reiner, Balcones Canyonlands Preserve Biologist

If you were intrepid enough to be outside on our coldest day of the winter to date, you might have seen something magical, like puffs of snow-white spun cotton emerging from the stalks of tall, dead weeds.  Those weeds are called Frostweed, and this is how they earned their name.  When temperatures are cold enough, the sap in the stalk will freeze, burst the stem’s outer wall, and spill out in an amazing variety of ice sculptures.

Each plant does this only once each winter, and only if we have a deep enough freeze.  Protected plants may survive a light freeze that hits the more exposed plants, so it is possible to see Frostweed sculpture a few times a season.  (Though the above-ground stem is killed by the freeze, the roots survive to sprout again next year.)  The sculptures are very fragile, and quickly melt when the temperature rises above freezing, or the sun warms them.  But we were “fortunate” on Thursday that the clouds and cold preserved them all day long.

If you saw the photograph of the Monarch butterfly last fall, you saw Frostweed in its other showy period, when flat-topped clusters of white flowers top stalks that can tower more than five feet high.  Their nectar is a big draw for Monarchs, and an important food source for them as they migrate southward.

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