How green is that salad in a bag?

We eat salad almost every night at dinner, but I am going to stop buying those already prepared bags of lettuce.  I like to go grocery shopping, and I do it frequently, and I admit I have been often tempted to buy those bags of pre-cut and washed lettuce, lined up in the grocery case, beckoning me by their ease at the end of a long day.  Once I get home, I could just open the bag, toss on an organic dressing and maybe some nuts and cheese and a few dried cranberries...but at what environmental cost?  I have been reading Michael Pollan's acclaimed book, "The Omnivore's Dilemma: A Natural History of Four Meals," and I just finished reading about how large organic farms produce all those bags of prepared lettuce on display at Whole Foods.  The energy expanded to pick the variety of lettuce leaves, wash and bag the lettuce, and then while keeping every single bag refrigerated it at 36 degrees, storing it and then shipping it from a farm in California all the way to the Whole Foods here in the mid-West where I shop is enormous!  Starting tonight, I will prepare my own salads from intact heads that I buy in the store, at the farmers' market or grow in my own garden.

I want to eat truly green lettuce.