Introduced in the 1800's, Black-Seeded Simpson Leaf Lettuce is one of the most popular lettuce varieties among home gardeners. Its bright green leaves stay tender and sweet at all stages, making it a great addition to salads and sandwiches. It's quick to mature and slow to bolt. To extend the harvest season, plant lettuce seed every two weeks. Lettuce is a cool-season crop that grows best in the spring and fall gardens. It's one of the easiest vegetables to grow and can also be grown in containers. 48 DAYS.