Leeks more than about 1 1/2 inches wide tend to have tough inner cores. The top green leaves should look fresh - avoid leeks with wilted tops.
Lemongrass grows in warm and tropical areas and is usually available fresh in the U.S. towards mid-fall.
Lettuce (in warmer climates), like other greens bolt and turn bitter when the weather gets too warm, making it in-season somewhere in the U.S. year-round. It can also be grown in low-energy greenhouses in colder climates through the winter.
Limes are harvested in semi-tropical and tropical areas in summer and fall.
Mushrooms (wild) have different seasons throughout the U.S. Most wild mushrooms other than morels are in-season in summer through fall.
Okra (early fall) needs heat to grow, so a nice long, hot summer in warmer climates brings out its best. Look for firm, plump pods in late summer and early fall.
Onions come from storage all year round but most onions are harvested in late summer through the fall.
Parsnips look like white carrots and have a great nutty flavor. Look for thinner parsnips, since fatter ones tend to have a thick, woody core you need to cut out.
Peppers (early fall) - both sweet and spicy- are harvested in late summer and early fall.
Persimmons are available for a short window in the fall and early winter - look for bright, heavy-feeling fruits.
Pomegranates only ripen in warmer climates. They are in season starting in October and are usually available fresh through December.
Potatoes are excellent storage vegetables, but most varieties are harvested in the fall.
Pumpkins are the most common winter squash and come into season in September in most areas.
Quinces area most under-appreciated fruit. Bright and tart, quince jellies and desserts are a fall and early winter favorite.
Radicchio, like all chicories, radicchio is more sweet and less bitter when the weather is cool.
Radishes (all types) are so fast-growing that they can be sown several times during the growing season in most climates. Fall marks the end of the season for small red radishes and the beginning of the season for larger daikon-type radishes.
Rutabagas also known as "yellow turnips" and "Swedes" are a sweet, nutty root vegetables perfect in stews, roasted, or mashed with plenty of butter.
Shallots are harvested in late summer and into fall, and are at their sweetest when fresh.
Shelling beans are those beans that can become dried beans but are briefly available fresh, as shelling beans, in mid-summer to early fall depending on your climate.
Spinach, indeed, has a season. It varies with your climate - year-round in temperate areas, summer and fall in cooler areas, fall through spring in warmers regions.
Sweet potatoes are often sold as "yams." They store well and are available from local sources year-round in warmer areas; from late summer through winter other places.
Tomatillos look like small green tomatoes with a light green papery husk.
Turnips have a sharp but bright and sweet flavor. Look for turnips that feel heavy for their size.
Winter squash of all sorts comes into season in early fall and usually last well into winter.
Zucchini have a harvest season from summer into fall in most climates.