Romaine or cos lettuce is a variety of lettuce that grows in a tall head of sturdy dark green leaves with firm ribs down their centers. Unlike most lettuces, it is tolerant of heat. In North America, romaine is sold as whole heads or as “hearts” that have had the outer leaves removed and are often packaged together.
Sow seed 1/8 inch deep , 1 inch apart in rows 12 to 18 inches apart. When plants have two or three true leaves, thin to 12-inch spacings for crisphead varieties, 6 to 10 inches for other types.