Iceberg belongs to the crisphead variety of lettuce. These plants form dense, compact heads of crisp leaves. Although not as flavorful as other lettuce varieties, iceberg is sometimes used as a base for salads or a crisp addition to sandwiches because of its crunch and mild flavor. It grows as a fall, winter or spring garden vegetable in U.S. Department of Agriculture hardiness zones 8 through 10. Following the correct planting tips can result in a healthy and abundant crop.
Lettuce thrives in the cool spring season so it requires planting in early spring once soil temperatures are above 60 degrees Fahrenheit. Iceberg lettuce also makes a suitable fall crop when planted in early fall after temperatures begin to cool. You can start head lettuces like iceberg indoors up to six weeks before you transplant to get an earlier start on the season. A well-drained bed that receives about six hours of sunlight provides the optimum growing location. Too much warmth can cause the lettuce to bolt prematurely, which typically occurs with iceberg when temperatures are above 75 F. A location that provides afternoon shade provides some protection of warmer temperatures in late spring.
Irrigation and Nutrients
Iceberg lettuce doesn't set deep roots, so it requires proper irrigation to keep the root zone moist. Watering the bed when the top inch of soil feels dry is usually sufficient. Depending on how cool and moist the weather is, the lettuce may require watering every five to 10 days. A deep watering providing about 1 inch of water allows the moisture to soak deeply into the soil so it dries out more slowly. Keep the lettuce heads dry when you water and avoid splashing mud onto the foliage. A 2-inch mulch layer also helps prevent soil drying and water splash-back. Mulch with compost covered by wood chips after planting. The compost supplies nutrients while the mulch retains moisture. A second application of compost as the heads begin forming provides more nutrients.
Although few pests bother iceberg lettuce, the ones that do can destroy the entire plant. Slugs and snails feed on the heads under cover of dark. Slug damage results in ragged, chewed leaves and weak plants. Commercial slug traps and bait prevent issues or you can pick the slugs off the plant by hand. Keeping the lettuce bed well weeded further minimizes pest populations near the lettuce. Diseases rarely affect lettuce plants, but keeping the leaves dry does prevent mildew and fungal infections.
Picking iceberg lettuce at the right time ensures full head formation and optimum flavor. Once the head bolts and sends up a seed stalk the flavor has begun to decline and the lettuce may taste bitter. Harvesting once the heads are fully formed and firm, but before temperatures rise above 75 F, ensures the largest plants while avoiding bolting issues. When cutting the plants, remove the entire head at the base. The outer leaves may be somewhat loose, but the inner head should feel tight and firm.
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