If the stem end of lettuce is turning brown it could be the beginning of lessening lettuce quality because of oxidation like an apple turning brown. Always check for lettuce firmness, wilting or decay. Once lettuce is cut, the plant ramps up an enzyme that triggers compounds that speed the aging of harvested lettuce and other greens. Bagged greens carry a slightly higher risk of bacteria. If you can, opt for unbagged lettuce, spinach or kale, and rinse at home. Then wrap your newly washed greens in a clean cloth towel and place them in a bag or container for the longest storage life.
Growing Home: Lettuce Oxidation
