Planting
Lettuce is a cool-season crop. While you should avoid planting in the middle of summer, you can get multiple crops in spring and late summer.
Take extra care if planting crisphead varieties; they will not survive a hot spell.
Start seeds indoors 4 to 6 weeks before last spring frost date for earliest crop.
Till in compost or organic fertilizer 1 week before transplanting.
Harden off seedlings for about a week, and transplant outside between 1 week before and 2 weeks after last spring frost.
Leaf lettuce: Plant 4 inches apart.
Cos and loose-headed types: Plant 8 inches apart.
Firm-headed types: Plant 16 inches apart.
Water thoroughly at time of transplant.
Fertilize 3 weeks after transplanting.
Direct sowing is recommended as soon as the ground can be worked. Plant seeds ½ inch deep. Snow won’t hurt them, but a desiccating cold wind will.
You should be able to sow additional seeds every two weeks.
To plant a fall crop, create cool soil in August by moistening the ground and covering it with a bale of straw. A week later, the soil under the bale will be about 10 degrees F (6 degrees C) cooler than the rest of the garden. Sow a three foot row of lettuce seeds every couple of weeks—just rotate the straw bale around the garden.
Consider planting rows of chives or garlic between your lettuce to control aphids. They act as "barrier plants" for the lettuce.