I usually tell clients that they should expect a new planting scheme to reach its peak three years after the inital planting, assuming the garden has been regularly maintained. At first the effect can often look rather sparse, with small shrubs and perennials surrounded by bare earth, but a year later their root systems will have become established and the plants will have filled out.
By the third season you should see the textures and volumes all working together to form a unified whole. Some of the more vigorous shrubs may then need cutting back having outgrown their allotted spaces and congested perennials can be divided and replanted.