Humidity is a huge component of lettuce lifespan. You can't just plop lettuce into your fridge near 0c as it is quite dry (hence why fridges have crispers that maintain higher humidity for veggies, and are selectable to low humidity for fruits).
Frankly, if you're not using a head of lettuce in 2 weeks something is wrong with your eating and/or buying decision making :-)
Frankly, if you're not using a head of lettuce in 2 weeks something is wrong with your eating and/or buying decision making :-)