Plants must have water to survive and flourish. Living, active plant tissues are usually 85 or 90% water, and even seeds, the least active form of plants, must contain 5 to 9% water to be viable. Plants use water for many things, including support for holding their leaves so that the maximum area is exposed to light for photosynthesis, transporting nutrients throughout the plant, and evaporative cooling. Nutrients must be dissolved in water before the roots can absorb them.
Effects of over watering
Although water is essential to plants, too much of it can be harmful. Over watering will enhance disease development, inhibit uptake of nutrients such as iron causing iron chlorosis, and contribute to leaching of soluble fertilizer and lawn chemicals to groundwater, particularly in sandy soils. These consequences happen because oxygen is only partially soluble in water and plant roots need some air-filled pores to insure that enough dissolved oxygen is maintained in the water film around the plant roots. When excess water fills the soil pores, displacing air, the roots cannot absorb sufficient oxygen for normal growth and may die due to asphyxiation. Insufficient oxygen levels also can stunt root system development, making the plant more susceptible to moisture stress later in the season even though early season was excessively watered.
Effects of water stress
Under watering can also contribute to disease development, and cause thin stands of poor appearing lawn and weak, unattractive landscape plants. Typical symptoms of water stress, or insufficient water, are drooping soft stems and leaves, and curling or rolling of leaf edges. On deciduous plants, the edges of leaves may dry out and turn brown due to tissue death, while evergreen leaves, like rhododendron, may scorch in winter. Flowers are reduced in size and number with inadequate watering, causing lower yields on fruit trees. Fruits or vegetables are generally less crisp and juicy when grown under water stress and are more susceptible to post-harvest defects.Inadequate soil moisture is often a major cause of winter damage. All plants, particularly evergreens, use water during winter, so it is important for plants to go into the winter with the soil profile adequately wetted. Under inadequate snow cover or dry conditions, winter watering may be required if the ground is not frozen.
For more general information on tree and lawn watering go to the Tree
and Lawn Watering page.