Fall 2009 was exceptional in two respects. The record drought of 2008–2009 ended suddenly in mid September, followed by heavy rains well into December. Then early December was exceptionally cold, with a hard 19° frost on Dec. 5 accompanied by heavy condensation frost on all vegetative surfaces (not to be confused with crystallofolia).
I had wondered why V. virginica in wet creek areas didn't exhibit crystallofolia in 2007, and suspected that the wet soil had managed to counteract the freezing air temperatures. In 2009, for the first time, I found frost formations at water's edge, as shown above. More speculation:
Perhaps the air temperature had lowered sufficiently to counteract the warmth from the water for the first time.
Since the springs and other water sources were dry until September, all water sources were from recent cold rains, and had little warmth to offer.
The late season moisture also caused blooming to occur very late. On Dec. 5 plants were still in bloom, stems had not yet hardened, and contained a lot of water. The frost formations were significantly larger than before and occurred almost along the entire stem. [Click images to enlarge.]
Dec. 5: Note the green leaves and frost formations high up the stem.
Dec. 20: Same area as above, leaves dry
Dec. 27: Same area
A large plant in bloom, 5 December 2009
Stem detail
And although the formations were larger than before, owing to the internal moisture, the condensation frost was also very strong and seemed to interact with the crystallofolia – restricting the fine detail of the ribbons.
Base of large plant, 5 December
Same plant as above, 20 December 2009
Stem base detail, 20 December 2009
Additional images for winter 2009–2010; click to enlarge.
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