Growing lettuce in containers is probably one of the easiest things to do in a container garden.  Very little space is needed to grow a few heads of lettuce, and because the roots are not very long, lettuce can be grown in relatively shallow containers.
A planter box like the one shown here (click on the picture for more information) can easily grow four or five heads of lettuce in it.   Just fill the planter box with some high quality potting soil (I prefer organic potting soil, but you can use what you want).

Plant the seeds about 1/2″ deep, and gently brush the soil back over the seeds.    Until the seeds germiniate, you can water by using a spray bottle set on “mist” (not “stream”).   Once the seeds have germinated, the soil needs to be moist, but not wet.

Once the lettuce heads have started growing leaves, you can start harvesting.  No need to wait for the entire head to grow.   Harvest what you can eat in a single sitting by just plucking the outer leaves off of the lettuce.  This will also encourage more growth in the remaining head.

Consider staggering your planting, so that you will always have a constant supply of edible lettuce.  To do this, plant your seeds a week or two apart.  This will give you access to some heads, while the others are beginning to germinate.  It will also give you lettuce a few weeks after your first heads have died off.

Recap: What you need to grow lettuce in containers

• You will need a shallow container.  If you don’t want to use a planter box, you can even use a plastic dishpan to grow lettuce in a container.
• High quality potting soil
• A sprayer bottle, to keep the seeds and seedling moist-but-not-wet