ETo measured in inches per day, week, or month. Low precipitation rate irrigation types work best for clay soils. The more established your plant is, the longer the roots are and the longer it can go between waterings.
Annuals are high water use plants in part because they have shallow, undeveloped roots.
Below that you will find mostly anchor roots, which hold the plant in place. A common misconception is that plants need to be watered more while you are trying to establish them. They do, however, need more frequent watering, as you do not want the roots to ever dry out until they are established. This is where you put all the information you have learned above together. A hydrozone refers to a group of plants with the same water requirement.