The Rule of Odd Numbers
A basic rule of thumb in landscape design is to work with odd numbers when trying to create a naturalistic appearance, as opposed to using even numbers which look formal, symmetrical, and regimented. Plant in groups of three, five, seven, or nine as opposed to two, four, six or eight. This is because even numbers are subconsciously divided into equal halves by the mind to reinforce a man-made, orderly aesthetic. Odd numbers cannot be subconsciously divided into equal halves, so the composition is interpreted as more naturalistic and the mass appears more unified.
EVEN NUMBERS This arrangement of four shrubs can be visually divided into equal halves by the mind.
ODD NUMBERS Since this arrangement of five shrubs cannot be divided into equal halves, it has a more unified, natural appearance.
This is a useful design rule to keep in mind because most homeowners are not trying to create a formal aesthetic with their landscape design. The terms “naturalized”, “flowing”, and “softened” are common adjectives used to describe many homeowners’ landscaping objectives, all of which are reinforced with an odd-numbered design approach. This rule of working with odd numbers does not just apply to plants. It also works with hardscape elements as well such as accent stones, planter pots, and elements within focal features.