|Schizachyrium scoparium 'Carousel' and Baptisia 'Midnight Prairie Blues'|
Here's a visual demonstration:
The steam was caused by evaporating hoarfrost in -6F/-21C on Wednesday morning. According to Wikipedia, radiation frost, or hoarfrost, forms on cold clear nights when radiation cooling causes objects (such as plants) to become colder than the surrounding air.
While snow is a gardener's friend, extreme cold is not. There hasn't been enough snow here this December, although about an inch of the dry, fluffy stuff fell last night.
|Hydrangea macrophylla 'Bailmer' (Endless Summer™)|