Frost requires a good source of moisture, like the fog seen behind this tree, and when the moisture condenses directly to ice, frost is created.
As the frost grows larger, it becomes hoarfrost, and it can cling to nearly everything, creating masses of delicate white crystals.
There were several very foggy, cold days this January, resulting in beautiful scenes like this country lane in Montpelier, Idaho.
This is the same tree as the previous photo, taken after the fog cleared, with Old Baldy mountain in the background. As long as the air temperature is low and there is no wind, hoarfrost can stay for days.
Simple objects like this barbed wire are transformed by a thick coat of hoarfrost. These photos were taken in temperatures ranging from about -7 to +20 F. All were taken in early morning before the sun and wind could destroy their delicate beauty.