Water is vital to ensure successful tree establishment, growth and fruit set. There are many reports of increases in girth of trees (important indicator of growth) over a growing season being highly correlated with rainfall, or a water deficit. Typically trees can extract water from the soil they are planted into for about 8 days in the absence of rain or irrigation. After this time period they begin to suffer from water stress. It is important to note that once visible injury i.e. leaf yellowing is observed as a result of drought then no amount of watering is likely to be successful! Regarding how much water to use - it has been calculated that large trees use up to 100 liters a day whilst a smaller species such as apple require about 5 liters. As a useful guide in dry weather 27-30 liters per day is recommended for larger trees.
If you are planting young trees then it is important to water the area the tree is to be planted. Cover and protect the roots of the tree to be planted. It is extremely important the root system of a tree does not dry out. Soaking the roots 5-10 minutes prior to planting and make sure the soil around the roots is not allowed to dry out completely for the first two years after planting. If water is limited then irrigation is best applied during leaf expansion i.e. early spring. If you are in doubt whether to water or not, there are a number of soil moisture probes that can be purchased inexpensively from any good garden centre. The probe should be inserted 0.5m away from the tree base. Simply water when the gauge moves into the red.
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