Lettuce-growing seasons are a bit tricky. Lettuce grows best when it's cool, but the leaves quickly dissolve when exposed to freezing temperatures. When it's too hot, lettuce bolts (goes to seed), becomes bitter, or dries up and dies.
Plant lettuce in early spring when the soil is about 60 to 80 degrees F and dry enough to work into a fine texture. For a continuous crop, sow seeds every week until temperatures get too hot for lettuce to thrive. Begin sowing again in late summer when high temps become a thing of the past.
To extend the season once the weather warms, add a shade cover such as netting or cheesecloth that allows light to penetrate but not burn the plants.
Planting lettuce from seed is easy. The plants emerge quickly—in about 10 days—so it's fun for kids to plant.
However, lettuce seeds are so tiny that it's hard to space them properly. It's easiest to put seeds in the palm of your hand, then use a pinch of your fingers to sparingly broadcast them so they're spaced about 1/2 inch apart in a row or seedbed.
Cover the seeds with no more than 1/4 inch of soil. Keep the soil lightly moist. A handheld sprayer is ideal for the task so the water doesn't move the seeds.
Keep the soil moist but not waterlogged as the lettuce grows.
Leaf lettuce is the easiest to grow and offers the widest array of colors, shapes, and sizes. It's ready to harvest in 40 to 60 days. It grows, as its name implies, in loose shapes that resemble single leaves. Exciting colors and leaf forms make leaf lettuce a great addition to a mixed salad.
Cut the leaves at ground level whenever they are large enough to use. Try not to pull the roots out, because this can dislodge the roots of other nearby lettuce plants. Cutting the lettuces also allows them to regrow new leaves several more times until warm weather stops their growth.
Romaine, or cos, lettuce grows with upright leaves that are often sweeter and firmer than other types of lettuce. It's the most nutritious of lettuces.
Butterhead lettuce and crisphead lettuce are a little more difficult to grow than leaf lettuce because they take more time to mature and are sensitive to heat. Both form rounded heads. Crisphead (think 'Iceberg' lettuce) is larger than butterhead lettuce, which gets its name because the inside leaves stay a lighter butter color due to lack of sunlight.
Mesclun simply means a mixture of varied greens. Mesclun can be purchased as a seed mix, or you can grow your mesclun garden with an assortment of lettuces and salad greens such arugula, chervil, chicory, and endive.
Its shallow roots and relatively small size make lettuce ideal for growing in containers. Grow it the same way you would in the ground, but use a soilless potting mix instead of garden soil, which is too dense and won't allow good root structure to develop.
Growing lettuce indoors is a little harder than it is outdoors unless you have grow lights. Most indoor light through a window—even direct sunlight—isn't as bright. However, lettuces grow inside when you keep the temperature below 70 degrees F and keep the soil consistently moist but not waterlogged.
Store lettuce unwashed in plastic bags in the coolest part of your refrigerator. Keep it away from apples, bananas, and pears. These fruits emit ethylene gas that quickly damages lettuce, causing it to decay.