Frost and Vertical Gardens
Frost affecting a wall depends on exposure. Some internal courtyards will do just fine.
A solution might include halogen or metal halide uplighting at the base that will generate heat to rise up the wall.
Tubes of hot water behind or within the system.
Large fans are sometimes used in agriculture to move air to mitigate frost.
Frost Sensors for Irrigation Systems
If you're planning for wall to go dormant in winter, than sensors might be a good idea.
Frost sensors are typically offered with most irrigation systems, so this would be very easy to implement.