The reason we cover our veggies when it's cold

Here are 3 pictures of a bed of chard that Mark did not cover during this last week's cold weather:

Here are 3 pictures of a bed of chard that Mark covered with 2 layers of Agribon 19:

The uncovered chard isn't dead, but it's not very happy either. The baby chard in the new bed came through unscathed.