Available year-round, spinach reaches its peak season in spring and autumn. There are two main varieties of spinach available at markets, some with thick, deeply crinkled leaves and others with tender, smooth leaves. Baby spinach -- small, immature leaves with milder, sweeter flavor and more delicate leaves -- makes an excellent salad green. More mature spinach is excellent sautéed or stir-fried, made into creamy soups, or chopped and cooked with pasta.
Select spinach with crisp and dark leaves free of bruises, tears and any wetness. For fresh salads, look for smaller tender leaves. For cooking, pick the larger and more flavorful leaves. If you are buying spinach in bunches, look for firm stems with a blush of pink at their ends.
Refrigerate the spinach unwashed in a plastic bag for 3 to 5 days.
As spinach leaves often trap soil and grit, wash them well before use. Fill a large bowl with cold water, immerse the leaves, and then lift them out, letting the grit settle at the bottom. Repeat with fresh water until completely free of grit. Spin dry in a salad spinner. Trim any roots and, if desired, remove the stems for a more delicate texture.