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In truth, establishment is a gradient, a plant's root-system continues to grow and 'establish' throughout the life of the plant.
In practical terms, the watering schedule should gradually change year-by-year towards less frequently, but more deeply.
Pomegranate (Punica granatum) can be a rather drought-tolerant tree or shrub, but if you are growing it to produce a crop, regular water will always be necessary in the growing season.