No matter how novice the gardener, he or she has taken to heart the “rule” that plants should be planted in odd numbers, with three as a minimum.
Perhaps a good rule, if the plants are small and unassuming, or if they have an upright, lonely air about them. But as Ralph Waldo Emerson said “A foolish consistency is the hobgoblin of little minds”. In other words, there are times when we are right to ignore rules and head down another road.
The “Wendy’s Wish” salvia pictured above, a magnificent garden plant, is so imposing on its own that one plant will suffice in a smaller garden. Three in a group would be overwhelming, for this plant has the size and presence of a shrub. I would say the same of Russian sage or some of the larger hardy garden mallows. Even in a container, as shown here Wendy’s Wish can reach 3 to 4 feet and spread a yard across.
Contrast this with the Mexican Petunia, Ruellia brittoniana, also in the photo. Though it will be clump forming beyond its first year in the garden, it is narrower and sparser than the salvia, and would be improved by planting in threes. It is root hardy here in Middle Tennessee, and will become a Traveller after a few years. But in the first year even a small garden could handle three. And for the thrifty, and those reluctant to spend $12.00 a plant. this plant roots in water in two weeks. It can be potted up then with no fuss, and after a week or so in a, pot, transplanted into place-
I believe that the more shrub- like a plant is, the more it can hold its own as a specimen that stands alone. Think of a tree peony. One would be lovely, three would be excessive, at least in a small bed.
Thoughtfulness and an attention to proportion should always trump Rules, even ones passed on as sacred-