The pigments that turn azalea leaves shades of red or purple are called anthocyanins.

As autumn’s first frost spreads across the southern United States, ice crystals form on the leaves of evergreen shrubs, such as this azalea. The pinks, oranges and yellows of their spring blooms have long since faded, but a new colourful display awaits as their green leaves turn shades of red and purple. For the plants, these pigments can help protect leaves against environmental stresses as temperatures drop. For gardeners, they create a vibrant autumnal display, framed in white frost. When spring arrives, fresh green growth will emerge, and the colourful cycle begins anew.