Mulching the soil around and between young lettuce plants with a layer of some organic material such as chopped leaves, compost, grass clippings, straw or even shredded paper helps keeps the soil moist and discourages weeds. Organic mulches that cover the soil over plant roots also improve soil structure, drainage and nutrients as they decompose over the season. They cool the soil by 4 to 6 degrees, which lettuce appreciates, and they keep soil off the lower leaves, reducing chances of disease from soil organisms. Peat moss makes a good mulch when mixed with coarser materials such as chopped leaves or shredded paper. Used alone, it tends to crust over and repel water.
For more information see file on Using Mulch In A Vegetable Garden.
Leaf lettuce needs consistently moist soil throughout the growing season. Lettuce that is allowed to dry out will turn bitter and go to seed (“bolt”). So if you go more than a week without rain you may need to water the garden every 3 to 4 days unless your soil has lots of organic material in it to hold moisture. Consistent moisture is particularly critical when butterhead types are forming heads. Check the top four inches of the soil with your finger or a houseplant water meter to determine if you need to water. Run a sprinkler or soaker hose system until soil is moist down at least 6 inches.
For more information see the file Watering Vegetables
Slow-acting granular fertilizer mixed into the soil at planting time provides a steady, consistent supply of nutrients for your lettuce, especially if your soil is rich in organic matter. Because lettuce is constantly generating new foliage as the mature leaves are harvested, it benefits from an extra fertilizer snack if you have the time. Spraying lettuce foliage with a liquid fertilizer every 3 weeks enables the plants to quickly absorb some extra nutrients which boosts their energy.
For more information see the file Fertilizing the Vegetable Garden
Almost all varieties of garden lettuce will grow right through the hot summer months, at least in the North, if they are shaded in some way during the hottest hours of roughly 10:00 am to 4:00 pm. Shade cloth which reduces sun exposure by 20% to 40%, is the best material for this job. Garden fleece, cheesecloth, and snow fencing (lath) also work.