As a horticulturist with a background in plant biology, I can provide an in-depth explanation of why lettuce and other greens may wilt. The process is multifactorial, involving both physiological and environmental aspects. Let's delve into the science behind it.
Firstly, water content is a critical component of lettuce and other greens. These plants are composed of up to 95% water, which is essential for their rigidity and structural integrity. When lettuce is cut or damaged, it loses water through a process called transpiration, which is the evaporation of water from the plant's surface. This loss of water can lead to wilting as the cells within the plant lose their turgidity.
Secondly, the cutting process itself can cause damage to the lettuce's cells and disrupt the flow of water and nutrients. When lettuce is cut, it can lead to a condition known as wound-induced senescence, where the plant starts to break down its own tissues in response to the damage. This process can accelerate wilting.
Thirdly, the presence of salt in salad dressings can indeed affect the texture of lettuce. Salt can cause a process called osmosis, where water moves from an area of lower solute concentration to an area of higher solute concentration to balance the concentrations. When lettuce comes into contact with a high-salt environment, water is drawn out of the lettuce cells and into the dressing, causing the leaves to wilt.
However, it's important to note that not all wilting is due to salt.
Temperature plays a significant role as well. High temperatures can increase the rate of transpiration, leading to a quicker loss of water from the plant. Conversely, very low temperatures can damage the plant cells and affect their ability to retain water.
Light exposure is another factor. Prolonged exposure to light, especially direct sunlight, can cause the lettuce to lose water more rapidly, leading to wilting. This is why it's often recommended to store greens in a cool, dark place to maintain their freshness.
The age of the lettuce also matters. Older lettuce will naturally have a higher respiration rate, which means they use up their water and nutrients more quickly. This can lead to a decrease in the overall water content of the lettuce, making it more susceptible to wilting.
Lastly, the variety of lettuce can influence its tendency to wilt. Some varieties are bred to be more resistant to wilting, while others may be more prone to it due to their physical structure and water retention capabilities.
In summary, the wilting of lettuce is a complex process influenced by water content, cutting, salt, temperature, light exposure, age, and variety. Understanding these factors can help in finding ways to maintain the freshness and crispness of lettuce for longer periods.
read more >>

According to him, crisp fresh greens go all limp because of salt in the salad dressing. The salt draws moisture out of the leaves, causing the plant tissue to weaken and the leaf to lose its crispness. ... But all greens will eventually wilt!Jul 21, 2009read more >>