How much and how often to water the avocado tree depends upon two variables: the weather and the type of soil in which the tree is planted. It may take several months to determine a suitable irrigation schedule. The avocado tree is of no help in the matter as the symptoms it displays when given too much water are the same as those it displays when it receives too little water, according to agriculturists with Texas A&M University.
Dig into the soil at the tree's drip-line (the area of soil that corresponds to the widest part of the tree's canopy) to a depth of 6 inches. Grab a handful of soil and close your fist. If the soil remains in a ball when you open your fist, you do not need to water. If the soil crumbles, it is time to water.
Place a soaker hose 1 foot from the drip-line and completely surrounding the avocado tree. Run the soaker hose for three hours.
Perform the soil moisture test again by digging into the soil, at the drip-line, to a depth of 6 inches and grabbing a handful. If the soil is moist, a three-hour irrigation with the soaker hose is appropriate. If it is overly wet or dry, adjust the amount of time the hose runs accordingly. It may take several attempts to find the appropriate schedule. Allow the soil to dry out prior to watering again.
Check the soil's moisture content more frequently during hot, dry weather.
Withhold water during December and January. Cold, wet soil makes the plant susceptible to root rot.