Repeating finely textured plants in a garden helps to unify the design and impart a powerful sense of simplicity. Repetition is simply a matter of holding one design quality constant while varying the others. Variety is the life of the garden. The design qualities of line, form, texture, scent, and color are changed and contrasted to provide diversity and avoid uniformity. Diversity develops a tension which helps to hold the observer's attention while creating excitement and enjoyment.
Variety is the opposite of repetition.
But when it is overdone by adding too many elements, chaos results, so a very fine balance between repetition and variety is needed to achieve unity in a landscape. Balance refers to the stability or repose of the garden, and is realized by creating an equilibrium between the parts that make up the whole. Line, form, texture, scent, and color all attract our attention so these sensual energies must be gauged and then balanced out. One form of balance relates to layout along a preconceived central axis. That axis can either be informal or formal in its arrangement.