During the growing season we think about the water needs of our plants. Because plants can be up to 95 percent water, water is critical to their growth, reproduction, and survival.
“Plants use water in three main ways: to maintain their plump shape, to carry water-soluble nutrients, and to carry out photosynthesis. A plump plant is upright, not limp. When plant cells have enough water, they keep their shape. When the cells lack water, they shrink and the plant wilts or loses its turgidity. By the time a plant is wilted, many plant processes have stopped and the plant will need some time to recover, according to the Plants in Drought article by Y. Rasmussen, UC Davis.
Turgidity arises from osmosis, where water moves from an area of high concentration to an area of low concentration. If there is more water outside the plant cell than inside the plant cell, water will flow into the plant cell until the two areas have the same concentration.
But the opposite is also the case. When the soil around a plant is dry, water from the plant cell migrates into the soil. Osmosis allows plants to take water from the soil and pull it up through the plant, eventually to the leaves, like sucking water up through a straw. As water enters the soil from the roots, the cells adjacent to the root cells also begin to lose water. This water loss continues throughout the plant until the plant wilts.
By the time a plant is wilted, many plant processes have stopped. If turgority is restored in time, a plant can recover. If not, a plant’s ability to transport nutrients is reduced or eliminated. Their ability to photosynthesize is impaired because the plant’s release of oxygen, which is a by-product of photosynthesis, simultaneously releases water vapor.
Normally, when the steam escapes, osmosis and other properties pull replacement water from the soil into the roots and up the plant. If there is no water available in the soil, the plant begins to “reduce non-essential functions such as growth and fruiting to vital processes”. Root activity stops and cells stop growing and multiplying.
A plant begins senescence – the onset of old age – and leaves, branches and roots begin to die back. Next, it prepares to drop those dead pieces. First it drops fruit, then leaves, and finally twigs. Eventually the whole plant may die” (Rasmussen).
Keeping the soil evenly moist throughout the growing season is important for good growth and production, based on the water needs of a particular plant.
— JoAnne Skelly is Associate Professor & Extension Educator, Emerita, University of Nevada Cooperative Extension. She can be reached at [email protected]