Amazing stuff!
Hoar frost or rime, mainly here...
hoar frost
ˈhɔːfrɒst/
noun
noun: hoar frost; noun: hoarfrost
a greyish-white crystalline deposit of frozen water vapour formed in clear still weather on vegetation, fences, etc.
synonyms: frost, ground frost, rime, rime frost, verglas; More
informalJack Frost;
archaichoar