Serving a watercress salad tonight? Here are some tips for getting the most from this salad green: Trim away the roots and swish them carefully in cold water. Discard any yellow leaves and dry with a towel. Store in one of two ways: Either lay clean leaves in damp cloth or paper towels and place in a plastic bag before storing in the refrigerator crisper or stand the leaves upright in a cup with an inch of water, loosely cover and refrigerate. Either way, use the greens within a day or two.