Iceburg lettuce doesn’t make a hard, dense head in Zone 8. This is because of the lack of growing time in the cold. It will grow in a looser head. Simply harvest the exterior leaves, and continue eating lettuce until the plant bolts, or sends its seed up in a shoot from the middle. At that time, you can discard the plant. If you plant lettuce in the fall, it will taste bitter. It needs cold weather to bring out the sugar in the leaves.
Organic fertilizer for the everyday gardener