There's something beautiful about growing and harvesting a whole head of fresh lettuce from the garden, and it can be well worth the wait, but for both an earlier and an extended harvest of salad greens, the cut and come again method can yield an abundance of leafy green goodness all season long.
Lettuce is one of those fairly simple to grow garden crops, as it doesn't require pollination or waiting quite as long as other veggies in order to harvest and enjoy, but if you want to grow head lettuce, it does take a bit of patience. If you're an impatient gardener, or want to extend your salad harvesting season, you might consider planting a bed or two with leaf lettuce that can be cut over and over again.
To grow head lettuce, each lettuce plant needs its own space around it, which can restrict the total amount of lettuce grown in a garden bed, and because many of the varieties are prone to bolting (sending up a flower stalk) once the heat of summer hits, harvests of head lettuce are often more suited to spring and fall, unless they're grown under shade cloth.
To grow lettuce with the cut and come again method, it's best to plant loose-leaf lettuce varieties (although head lettuce varieties can also work), and to use mesclun (mixed) lettuce seed to provide some variety in color, texture, and flavor. The rows of cut and come again lettuce can be much closer together than head lettuce (as close as 4 to 6 inches apart), and the seeds can be planted much closer together as well, so there's no thinning necessary.
Prepare a garden bed as for any other seedlings, then lay out your rows and plant the seeds close together, either in a single row or as a 4 to 6 inch band. Once the leaves have reached the size of baby greens (about 4" long), the outer leaves can either be harvested individually (takes a lot longer), or can be cut one handful at a time with garden shears or scissors, about one inch above the crown of the plant (cutting into or below the crown will most likely kill the lettuce plant). I like to start at one end of a row and loosely grab a handful of leaves and cut them with scissors, which is a quick and efficient method of harvesting them, especially if you have a big garden bed.
One of the keys to growing a perpetual harvest of lettuce with the cut and come again method is to not plant all of the rows at once, but to instead start several rows (depending on the size of your household) each week or every other week. This way, you'll always have a row or two ready to cut when you want fresh greens, and will allow the rows you've previously cut to send up a new batch of leaves for future harvests. Different varieties and gardens in different climates will have different growth rates, but a general rule of thumb is that new lettuce leaves will be ready to harvest again about two weeks after cutting a row. It's possible to get at least four cuttings from each planting of lettuce, and possibly more, depending on your weather and garden conditions.
To add some variety to your cut and come again lettuce beds, consider using a spicy greens mix with mustard or other 'bitter' greens, adding some chard or spinach seeds to the rows, or planting radishes either between the rows or in the rows, which can be harvested as soon as a couple of weeks.
Before the weather really heats up in the summer, rows of lettuce can be covered with shade cloth or row covers, which will slow the plants' tendency to bolt and extend the harvest into the hot season. Once the lettuce begins to bolt, you can either let them go to flower to nurture the pollinators, and to set seed (which can be saved for next year's planting if they are a non-hybrid heirloom or open-pollinated variety), or the plants can be pulled and fed to chickens or the compost pile. As fall approaches, more rows of lettuce can be planted and grown under row covers, or existing beds can be covered with row covers or low tunnels to extend the harvest well into the cold season.