Delicate needlework

Needle-like ice crystals form on holly leaves as hoar frost, creating a pristine sparkling effect in a winter garden. This natural phenomenon can occur on nights when the air temperature drops to between -1°C and -6°C. Water vapour is deposited on the leaf and small ice crystals form on certain parts, such as the leaf edges. The sharp points of the holly in particular are ideal sites for crystals to form in this temperature range. From these growth sites, the needles extend outwards when there is sufficient moisture in the air and the nights are long. This is likely to occur in December.