What Makes a Plant Wilt?

Wilting

• Wilting is when a plant stem or leaves loses its turgidity, causing its leaves to curl up or allowing its stem to bend over and collapse under the plant's weight. The loss of water inside the plant's tissues causes the of plants loss of turgidity. Sometimes, only a specific branch or stem of a plant is affected but, most often, the whole plant wilts at once.

Vascular Systems

• One of the biggest changes in the evolution of plants is when they developed vascular systems, allowing multi-cellular land plants to grow taller than mosses, hornworts and liverworts, all of which are confined to being only a few inches tall. There are two major types of vessels in plants: xylem carries water and nutrients up from the roots to all the living cells of the plant while phloem carries sugars and other products from photosynthesis from the leaves to the roots.

Stomata

• Plants use transpiration as the force to move water from the roots up into the leaves, flowers, stems and fruit of the plant. Transpiration occurs when the stomata, a pair of guard cells which open and close, allows the exchange of gases -- oxygen is released and carbon dioxide is taken up -- and permits water vapor to escape. When the water vapor escapes through evaporation, the hydrogen bonds between the molecules of water pull the adjacent molecules up the plants vessels. When the stomata close, transpiration is reduced although there is still some evaporation going on through the surface of the leaves. Very waxy leaves have less accidental evaporation than thin, uncoated leaves.

Over- and Under- Watering

• Both over- and under-watering can lead to plant wilt. How under-watering causes plants to wilt is more intuitive than how over-watering can lead to wilting. If a plant is under-watered, the normal processes of opening their stomata to allow gas exchange will eventually lead to wilting because there simply isn't enough water available for filling up all the plant's cells. The plant can control this to some extent, but it can't photosynthesize without exchanging gases.

  Somewhat surprisingly, over-watering can be just as problematic for a plant. Plant roots need oxygen to survive. Because land plants' roots have developed strategies for finding water in mostly dry habitats, they can't handle being constantly wet. Without access to air, and oxygen, the plant roots rot. Once the roots have rotted, there's no way for the plant to take in more water and, as transpiration continues, the plant wilts. Wilting can also be causes by damage to the vascular system due to infection or physical damage.