Although not perfect, your senses are typically the most trustworthy instruments for determining whether or not your lettuce has gone bad. Discoloration, a soggy texture, and a rotting smell are all prominent characteristics of poor lettuce. Lettuce will initially go limp, and the green tint will fade to brown or black. As it continues to decompose, so will the color until only the white core remains. Lettuce can also be bad if it has any of these defects: holes in the leaves, broken or shriveled leaves, or torn or wilted flowers. These problems signal that insects have been eating the plant. The insects either damage the lettuce themselves or carry viruses that can be passed on to humans through bites. Finally, lettuce can be considered bad if it has any kind of odor. This usually indicates a problem with moisture or fertilizer, but it can also be an indicator that something is wrong with your lettuce. If it has an odor, remove from the garden and allow to dry out before disposing of. Good lettuce should remain crisp with a bright green color. If it starts to get limp or yellow, then it needs to be replaced.