Many years ago, conventional wisdom held that perennials should be planted in groups of three. The reasoning behind that advice was simple: Planting one perennial would look scrawny. Planting three in a grouping would show better.
That makes sense if one has a large estate with flower borders 8 feet deep by 20 feet long; such gardens can accommodate elaborate plant groupings. However, some gardeners have small urban lots that cannot hold most of the perennials on their wish list, let alone three of one kind. Other gardeners have strict budgets that barely allow for the purchase of one new perennial each season. Could there ever be a compromise on this matter?
Instead of a compromise, there has been a revolution. A new generation of gardeners, that had been raised by irreverent parents, who, themselves, were encouraged to do your own thing, are realizing that there are no rules of gardening; we all can do as we please. Our gardens are private oasis for lovers of plants. Inside these retreats, gardeners make their own rules to create personal spaces that make them happy. Some rebel gardeners have resorted to planting only one of a plant, simply because they can. Others do the same because space is limited.
If we want beautiful flowerbeds, however, there is one rule that needs to be respected. Gardeners who have the space and the budget for more than one of the same perennial are encouraged to plant them in odd, instead of, even numbers. That is, unless they are creating very formal gardens that rely on symmetry. While there is no consensus as to which field of science this rule belongs to, there is consensus that it is a fundamental rule of design. Here is what we have come to understand:
In determining what makes a garden beautiful, we take our inspiration from nature, which has a natural chaos about it. Nature appears less ordered and has a less managed look. However, the human brain instinctively tries to impose order on chaos. It does so by pairing up even numbered items to create formal patterns, because even numbers are easy to divide in the brain.
Because nature embraces chaos, odd numbers look more natural. At first, odd numbers of an item appear unbalanced; they are more difficult to divide because the eye is unable to pair them. When the eye tries to group an odd number into pairs, there is always one left over; the eye continues moving everywhere looking for a mate. This creates a pleasurable dynamic situation. The resulting phenomenon is that odd-numbered groups are particularly pleasing to the eye.
Theories vary as to why. One theory is that having an odd number forces one to view the objects as a single group, rather than visually dividing them into two separate sets. Another theory is that odd numbers look less regimented than even numbers. Twined objects appear static; odd numbered groupings come to life, resulting in compositions that are more aesthetically pleasing. Because the brain automatically breaks down what it sees into pairs, if we plant only two, our eyes will be fixated on the pair and we will ignore the rest of the garden. An odd number of plants stimulate the brain to look everywhere.
In adapting this rule of nature, it is not always necessary to plant in groupings. Successful compositions are possible when three, five or seven of the same, or similar, plants are sprinkled throughout the flowerbed. This creates a rhythmic repetition that draws the eye through the garden, while at the same time, unites all of the plants into a successful and eye-catching composition.
Creative gardeners, with long wish lists but limited space, may opt to plant odd numbers of different kinds of perennials, all of which share a similar color and bloom time. The brain will see an odd-numbered grouping of flowers in the yellow family, for example, before noticing that the flowers and their colors are not identical. Jean Potuchek used this technique to great advantage when she planted yellow Hemerocallis in her blue and yellow border. Click to see the picture of this composition in the photo-banner at Jean’s Garden. It reinforces how effective odd-number planting can be.
A general rule of thumb is to use even numbers to design a formal garden and odd numbers for an informal one. Many gardeners fume whenever they read or hear advice about planting in odd numbered multiples of three, five, or seven. They believe this to be just another silly rule that has become outmoded. Not so! The rule should be respected because it makes our gardens beautiful.
The copyrighted photo, at the head of this post, that illustrates the effectiveness of using odd numbered items, is the work of UK garden designer Claudia de Yong of Claudia de Yong Design, who also blogs at The Garden Spot.