Cos Lettuce Red and green - Buzzy Patio Vegetables. A vegetable garden on your balcony, rooftop terrace or in your garden? Cos Lettuce can be grown in pots, tubs, plant sacks or in a square metre garden. Sow under glass from February to March, or in open ground from mid-March to early-August. A crisp, flavourful and healthy summer snack. Moonred and Little Gem.