A favorite in all types of gardens, including children's gardens and container gardens, lettuce is easy-to-grow, nutritious and can be harvested at the baby leaf stage in just 30-40 days after sowing. A cool-season vegetable, lettuce seed can be sown in the garden in early spring as soon as the ground can be worked. To ensure a longer harvest, sow lettuce seed every two weeks throughout the spring. Lettuce can also be planted in late summer for a fall harvest. When choosing lettuce seed to buy, choose from a variety of lettuce types including loose leaf, butterhead, romaine or cos, and crisphead. Lettuce can be grown in the garden, raised beds and containers.