How do I keep my Green & Red Leaf Lettuce from Wilting?

I love the dark greens, Red Leaf, Green Leaf, Romaine Lettuce and Spinach. I buy Organic and put them in the refridgerator in the crisper, and I turn the knob to vegetables (to control the humidity I guess) I dont keep them wrapped in plastic - But within 1-2 days they get all wilted and soft. What am I doing wrong? Help!