How Does a Frozen Leaf Survive?
We're used to seeing frost on leaves, but the threat of that ice is real.
When the temperature drops below the freezing point of water, young budding plants face a crisis. Before freezing, that water was comfortable, easily handled, perhaps even beneficial to the internal health of the young leaves. But once it freezes, it’s not water any longer.
This creates forces that try to pull water out of the leaf to balance osmotic pressure inside and outside the leaf. (Water wants to flow out of the leaf into the dryer area outside.) For a tender plant, or a very young bud, this might mean the end. But most plants in temperate regions have some tricks that allow them to fight for their survival.
In addition to evolutionary improvements (later budding, or a tougher skin), plants actively deal with the freeze by changing their internal chemistry. The cells in the leaves make chemicals that are, basically, anti-freeze. Despite the ice on the outside, the inside of the cells remains liquid. The chemistry of this is complex, but in simplest terms, it lowers the freezing point inside the cells. Some of the chemicals also slow down the movement of water out of the leaf and into the ice forming on the outside.
If the freezing doesn’t last too long, such a frost-tolerant plant will survive for another day.
Shot in my back yard in Orting, WA with the Sony A7RIV and 70-200mm lens at f/4.5, ISO 100, exposure 1/125th second. The depth of field was limited, so I took two shots with slightly different focus and combined them. This puts the full leaf cluster in the zone of focus. This was done handheld; I just leaned back an inch or two to get the different area in focus.
Here’s a link to a very deep dive into leaf survival in freezing conditions.