Irrigating California avocado trees can be challenging for several reasons. Avocado trees are heavy users of water but they have a shallow feeder root system located primarily in the top six inches of soil that are prone to drying out. The feeder roots also have very few root hairs, thus making them inefficient at absorbing water. Hillside groves with decomposed granite drain well, but they drain rather quickly. Groves with high clay content can suffer from poor drainage that leads to root rot.
For the above reasons, monitoring soil moisture in avocado groves is important.