Rhythm is created when a feature is repeated and the line that is created forms a pattern that is appealing to follow with your eye - this creates a sense of flow around a garden.
Close together and upright repeated elements create an exciting and dynamic rhythm, they create a strong focal point.

Widely spread and lower repeated elements create a calmer, more sedate rhythm.
Use rhythm in a garden to give a sense of direction to movement, alongside a path or connecting two areas of the garden together.