Black-Seeded Simpson has been THE favorite lettuce variety of gardeners since at least 1900. It is generally considered the primary heirloom lettuce variety. Leaves stay sweet at all stages of growth and plants are slow to bolt (flower). Black-Seeded Simpson plants are upright and compact with light-green, curled leaves. Heat tolerant. Great for containers. Black Seeded-Simpson is THE best lettuce variety that you can grow! 45 Days.