I noticed the leaf response to cold right away. For my specimen, and in this area of NY, the leaves curl at around 25 degrees. Very cold winter nights, leaves can be nearly completely closed, then open if the afternoon "warms" to about 30. Leaves will also curl when the plant needs a drink during rain-free hot summer weather. I'm sure the amount of water the plant is getting in winter slightly changes that temperature range for the leaves to open and close.
I noticed the leaf response to cold right away. For my specimen, and in this area of NY, the leaves curl at around 25 degrees. Very cold winter nights, leaves can be nearly completely closed, then open if the afternoon "warms" to about 30. Leaves will also curl when the plant needs a drink during rain-free hot summer weather. I'm sure the amount of water the plant is getting in winter slightly changes that temperature range for the leaves to open and close.