Water Adheres To Soil
Watering the yard and garden is not all that complicated if you understand a few basic principles about how water penetrates the soil. Soil fills with water from the top down. The force of gravity causes the water to seep into the soil. Where it meets individual soil particles, water forms a thin layer around each microscopic particle. Under good drainage conditions, soil will hold back a definite amount of water against the force of gravity, this is called its field capacity, and this capacity varies with differing soil texture and structure.
Plants Take Water By Suction
Plant roots use the power of suction to take water away from those soil particles until the water film is so thin that no more water can be sucked up by the plant. It is a regular war of the worlds down there, with soil and roots fighting for droplets of water. The landscape gardener must make sure there is always enough water to satisfy the needs of the root systems, but not so much water that oxygen is denied to those same roots.
Soil Loses Water From Top Down
While the soil acquires water from the top down, it simultaneously loses water from the top down. Water is also lost aboveground through transpiration by plant leaves and through evaporation from the soil surface. The rate of water loss depends on the temperature of the air and soil, the amount of humidity in the air, the amount of wind, whether it is cloudy or sunny, and whether the plant is mulched.
pH Can Make A Difference
If you irrigate with hard water, water your acid-loving plants such as rhododendrons and azaleas with a mix of one cup vinegar to a gallon of water weekly to help keep them bright green and glowing.