Cos or Romaine lettuce is a variety of lettuce that grows a taller head of firm leaves. It also tolerates heat, unlike most other varieties of lettuce. The heart of the cos lettuce with the outer dark leaves removed, is known as a baby cos lettuce and is a touch sweeter than the outer leaves. They are very easy to grown yourself, we have a small back yard and grown them in pots. Harvest when the leaves are crisp and head is full of colour (the more mature the plant the more bitter the leaves).