Lettuce thrives in the cool weather of early spring or fall when average temperatures are between 60 and 70 degrees Fahrenheit. In hot weather, the leaves are bitter and the plant goes to seed. Leaf lettuce, Cos or romaine lettuce, and asparagus lettuce all grow readily from seeds planted directly in the garden. Head lettuce needs to be started early in a greenhouse or cold frame and transplanted into the garden in the spring.
Work the soil to loosen it and break up any hard clumps. Add 3 to 4 lbs. of 5-10-10 fertilizer per 100 square feet of garden space. Form rows 12 to 18 inches apart, or plant in a square pattern.
Sow the seeds 1/4 inch to 1/2 inch deep, approximately 10 seeds per foot.
Water the seeds gently to avoid disturbing the seeds. Keep the soil moist until the lettuce sprouts.
Thin the seedlings when they sprout to approximately 4 to 8 inches apart. Leaf lettuce needs less space, Cos and Butterhead need more. Use the thinned plants in salads.
Continue watering the lettuce daily or every other day. Lettuce needs frequent shallow watering. Mulch with a layer of organic material to discourage weeds and conserve water.
Hand-pull weeds as they appear or lightly hoe between rows. Avoid disturbing the lettuce roots.
Harvest lettuce as you need it. Young, tender plants are best. Cut the plant at ground level with a sharp knife or scissors.