“Lettuce is like conversation," wrote humorist Charles Dudley Warner. "It must be fresh and crisp, so sparkling that you scarcely notice the bitter in it." As the weather heats up, lettuce tends to become acrid, tough and sun-bleached, eventually bolting or going to seed. Luckily for fans of summer salads, there are a few tricks to keeping your greens tender and refreshing through all but the strongest heat waves.
Choose heat-tolerant varieties
Lettuce is perfect for succession planting. When there's no more danger of frost, plant rouge d'hiver, summertime, saladbowl or other heat-tolerant lettuces. Look for a mesclun mix that performs well in your climate, and harvest it while the leaves are small for best flavor.
It's nearly August, but my lettuces are holding strong in the shade of nearby sunflowers. Lettuce doesn't need full sun; in fact, it'll perform better if you give it indirect light and cool shade. Plant summer lettuce underneath tall plants or arbors, or make your own shade structure. Some gardeners keep their lettuce in container gardens, which can be moved to shady spots in warm months.
From the Organic Authority Files
Cut and replant
Loose leaf lettuces -- the ones that don't form a head -- should be picked continually as they grow. Cut off the outer leaves when they're 4 to 6 inches long, leaving smaller inner leaves. This tricks your lettuce into thinking it hasn't matured, keeping it from bolting. As a last resort, dig up the entire plant and replant it in a new spot, which will cause it to focus on growing new roots instead of going to seed.
Water, water, water
Just like you, lettuce is largely composed of water. Don't skimp on watering, particularly if you live in a dry climate. Lettuce roots are shallow, so you don't need to water deeply. In extreme heat, though, you might need to douse them more than once a day. To help stop the soil from drying out, mulch with newspaper or cardboard.