For the above statement to be true in the case of a tree, the proper amount of water and techniques of watering need to be applied. Water provides the means for a tree to absorb essential nutrients which give trees the ability to grow strong healthy tissue and fight off disease. Some trees, like large cottonwoods, can drink hundreds of gallons of water a day if allowed. Other trees though, if watered too much, can drown and decline rather quickly. Plant species and size, soil texture, air temperature and humidity all play an important roll in determining the proper amount of water.
The first step in determining the proper amount of water is to know the soil type that the tree is planted in. By this I mean soil texture. The two ends of the soil texture spectrum are very fine clay soils which retain moisture well and very coarse sandy soil which do not retain moisture well. By determining soil texture, you can then know how best to reach field capacity. Field capacity is reached when the ground is at its limit of water-holding capability and all other excess water has drained away. Clay soils have a greater water-holding capacity than sandy soils do therefore sandy soils need to be watered more frequently.
The most basic principal of watering is that enough water should be supplied to the soil to replace what the tree uses and what is lost to evaporation and percolation. Newly transplanted trees of any species require frequent water addition, especially within the root ball. The same frequency of irrigation on many mature specimens can lead to problems, however.
As a rule, frequent, shallow watering encourages surface rooting, making the tree more vulnerable to desiccation or drying out during periods of drought. Infrequent, deep soakings encourage the production of a deeper root system and more drought tolerant trees. Also, if the soil is allowed to dry between watering, natural shrinking and swelling occurs improving soil structure. Conversely, frequent, shallow irrigation tends to compact the soil surface and reduce the rate of water infiltration.
The most beneficial time to irrigate plants is during the late night and early morning hours so to reduce evaporation. Saturation of foliage should be avoided during mid-day hours to avoid burn. Water should be distributed evenly to as much of the root system as possible. Watering the lower trunk or root collar should be avoided because it can lead to increased fungal decay problems for the tree. The water application rate should not exceed infiltration rate. If water is applied too quickly, run off can occur causing erosion problems and reduce infiltration. Puddling or runoff that results from too high of application rates wastes water and can be detrimental to root growth. One very simple technique for watering effectively is to place a hose at the base of your tree, or in between several trees, and allow water to flow slowly over night. This can be done once a week for trees with large water requirements. Supplemental watering once every two weeks or even once a month can dramatically improve tree health. Another technique utilized by many arbor companies is high-pressure water injection, which can deliver large amounts of water directly to the root zone rather quickly. Drip irrigation and tree specific sprinkler systems are other methods that can be used to maximize watering efficiency.
If you are unsure about the best method and proper amount of water to use for your landscape gems it is best to consult your local certified arborist. ISA certified arborists are taught and know the best way to maximize the health and extend the life of these great assets to our environment. The International Society of Arboriculture (ISA) is a world wide professional organization dedicated to fostering a greater appreciation for trees and to promoting research, technology and the professional practice of arboriculture.