Sowing spinach and lettuce

With all of the spaces freed up from tomatoes and melons, I had the equivalent of a full garden box available. This was planted with several varieties of lettuce and spinach. Overall, I planted about 70 lettuce and 18 spinach. I am interested to see if these will mature before the weather gets really cold and will be experimenting with some form of inexpensive greenhouse or row cover to extend the season. The goal is to have enough greens to pick throughout the winter.