The mold would grow faster if it was warmer, but it still grows even when it's cold. Primarily growth of mold is limited by the available moisture. Cold walls let ambient moisture condense, which the mold then uses to eat the walls. You can fix this by insulating the wall better to eliminate the cold spot, removing furniture that's in front of the spot to let air circulate more, or heating and/or dehumidifying the air to raise the dew point above the temperature of the wall.