It doesn't really matter where you live, you can always have some sort of fresh food. Lettuce is a nice easy food to grow and it will happily take off in a windowbox. Thanks to shallow roots, lettuce is ideal for the gardener with minimal space. Even if you live in a basement suite, you can take advantage of the little light you have to grow some of your own food for salads.
Choosing Your Lettuce
There is no reason to stick with just one type of lettuce. I actually think a salad is far more appealing with different colors and textures. Leaf lettuce will be easier to grow in a windowbox than ones that form heads, but apart from that, you are really able to choose anything you like. Some favorites of mine include:
Boston - This is a nice big leafed variety that is green and very light on flavor.
Oak Leaf - With longer leaves that have ruffled edges, this is a nice sweet lettuce.
Red Leaf - Slightly on the bitter side, this lettuce adds a nice color variation to any salad.
Take a look online or at your local nursery to get some ideas as to what types of lettuce you'd like to grow.
Growing Your Lettuce
Lettuce doesn't need very deep containers, which makes it ideal for windowboxes. You don't actually have to use a windowbox, though. All you need is a container that will fit in your window and is 6" deep.
A sunny window is best, but you'll find that these plants grow pretty well anywhere there is lots of natural light.
You can use regular potting soil, but be sure to use rocks at the bottom of the container. This will help with draining since lettuce plants really don't like being overwatered. If you want to mix some perlite into the soil, it will work, too.
Plant the seeds about an inch apart and just barely cover with soil. They actually need some light in order to germinate. Water the plants thoroughly and then keep the soil moist. Dry soil results in bitter lettuce.
Your lettuce should be ready to harvest in a month or two, depending on which variety you chose. But don't just pull it out! You can make your lettuce last longer by using scissors or a sharp knife to cut the leaves about an inch above the base. Eat your leaves in salad and the plant will grow back within a couple of weeks. You can do this several times before the plant dies off.