With their high water content, lettuce and other leafy greens have a tendency to spoil quickly. Keep salad greens fresh by storing them in moisture-absorbing paper, and ideally in a lettuce crisper in the refrigerator. You can freeze chopped up greens with a little water in ice-cube trays for quick and easy adding to stews and slow cooker meals. Salad greens that have lost their crunch are also great in smoothies, giving your morning drink an additional nutritious punch.