Iceberg lettuce is a popular crisphead variety prized for its signature crunch and mild flavor. Growing this type of lettuce at home yields fresh, dense heads. Success relies on understanding its specific needs as a cool-season crop, particularly regarding soil quality, spacing, and temperature control. This guide outlines the steps for cultivating crisp and flavorful iceberg lettuce from seed to harvest.
Preparing the Planting Site
Iceberg lettuce thrives in conditions that provide ample sunlight while keeping the roots cool. The ideal location receives full sun during the cooler spring and fall months, requiring at least six hours of direct light daily. If planting extends into warmer periods, partial shade, especially during the intense afternoon hours, is necessary to prevent heat stress and bolting.
Lettuce has a shallow root system, requiring consistent moisture without becoming waterlogged. Use a well-drained, loose, and fertile soil rich in organic matter. Aim for a slightly acidic to neutral pH range, ideally between 6.2 and 6.8, for optimal nutrient uptake. Incorporating one to two inches of well-aged compost into the top six inches of soil before planting improves both drainage and fertility.
Sowing Seeds and Managing Seedlings
The optimal time for planting iceberg lettuce is in the early spring, as soon as the soil is workable, or in the late summer for a fall harvest. Seeds germinate best when soil temperatures are between 55°F and 65°F; temperatures exceeding 72°F can inhibit germination. For an early start, seeds can be sown indoors four to six weeks before the last expected frost date.
Seeds should be planted shallowly, about 1/8 to 1/4 inch deep, as light aids germination. If direct-sowing, place seeds about one inch apart in rows spaced 12 to 18 inches apart. Once seedlings develop two or three true leaves, thinning must occur to allow for proper head formation.
Thinning involves removing weaker seedlings to leave the remaining plants spaced 10 to 12 inches apart. This wide spacing is necessary for the head-forming varieties to fully mature into dense, crisp heads. The removed thinnings are edible and can be used as baby greens. If transplanting indoor-started seedlings, harden them off for about a week before planting outdoors at the same 10 to 12-inch spacing.
Watering and Feeding Requirements
Consistent moisture levels are paramount for growing sweet, crisp iceberg lettuce and preventing bitterness. Since lettuce roots are shallow, the soil must be kept evenly moist but never soggy. Inconsistent watering, particularly drought stress, is a primary trigger for premature bolting, where the plant develops a tall seed stalk.
Plants generally need about one inch of water per week, requiring increased frequency during hot or dry weather. Applying organic mulch, such as straw or shredded leaves, helps regulate soil temperature and retain moisture. Lettuce benefits from nutrients that support vegetative growth, particularly nitrogen.
Mix a light application of a balanced, slow-release fertilizer into the soil at planting for initial nourishment. Supplemental feeding with a diluted liquid fish emulsion or seaweed fertilizer every few weeks can boost growth. If a heatwave pushes daytime temperatures above 75°F, use a light shade cloth to keep plants cool, delay bolting, and preserve the mild flavor.
When and How to Harvest
Iceberg lettuce is ready for harvest between 70 and 90 days after planting, though this timeline varies based on cultivar and local conditions. Maturity is indicated by the formation of a firm, dense head that feels solid when gently squeezed. Harvesting too early results in a smaller yield, but waiting too long, especially as temperatures rise, risks the plant bolting.
Harvest in the early morning when the leaves are crispest from the cool nighttime temperatures. Use a clean, sharp knife to cut the entire head cleanly from the base of the plant at the soil line. Unlike loose-leaf varieties, iceberg lettuce is a one-time harvest crop and will not regrow a new head once the main one is removed.
The remaining root and stem can be removed from the garden. The harvested head should be immediately chilled in cold water to preserve crispness, then stored in the refrigerator.