3, 5, 7, 9: Magic numbers for a successful perennial garden

Why these figures?

When it comes to planting in groups, you will often hear numbers such as 3, 5, 7 or 9. But why these numbers, you may ask? Well, my dear Watson, the answer lies in a combination of science and art!

First, these numbers are odd. In mathematics and in design, odd numbers are frequently used to create balance without symmetry, which is generally more pleasing to the eye. Next, these groups of plants, for example three lavenders side by side, create a visual mass that has more impact than if those plants were solitary. Grouping gives the illusion of abundance and density, qualities sought in a well-designed garden.

Moreover, planting in groups is much more practical. Plants with similar needs for water and light, for example petunias and begonias, can be grouped together to simplify care. This method not only reduces time spent on maintenance but also optimises use of water and nutrients.

Ultimately, planting in groups is not simply a matter of following a tradition or an arbitrary rule, but a way of harnessing principles of nature and design to create a garden that is both beautiful and functional.

Details of magic numbers and their specific uses

Three: the power of three

The number three is often the starting point for creating a minimalist effect without sacrificing visual impact. Three plants of the same species and variety, for example three agapanthus, can be planted to form a small triangle. This arrangement creates visual unity while leaving enough space for each plant to develop. Moreover, three plants attract the eye more than two, without creating an impression of crowding or disorder.

Five for balance

Five is the ideal number for those seeking to create a more complex visual balance. Take, for example, five peonies planted in a staggered pattern. This arrangement provides both structure and depth to the garden. Moreover, five plants also allow play with different heights, contrasting for example with three shorter plants nearby.

Seven for abundance

A group of seven plants creates an impression of abundance and fullness. Ideal for large borders or open spaces, a group of seven also allows mixing several varieties for an even more dramatic effect. You could, for example, combine three pink Astilbes with four white Astilbes (seven in total) for a play of colours and textures.

The charm of nine for large plantings

The number nine is generally reserved for large spaces or gardeners seeking to showcase a plant in a bold way. Take one example: a group of nine Iris can serve as a focal point in a large garden, attracting the eye from afar. The number nine also allows greater diversity, offering the opportunity to combine several sub-groups of three different plants (for example three varieties of three Iris) to create a patchwork effect.

Advantages of planting in groups

Aesthetic impact

Aesthetics is one of the main reasons many gardeners choose to plant in groups.

Example: Take a group of 5 Daylilies, placed behind a group of 3 Hydrangeas. This arrangement creates visual harmony, with the Hydrangeas providing volume and a rounded shape, while the Daylilies add height and contrast with their long stems and trumpet-shaped flowers. Such staging plays on differences of form, colour and texture to create a composition more captivating than a simple row of plants.

Another important point is the effect of repetition. Rather than scattering the same type of plant, such as Salvias, randomly across the garden, grouping an odd number of these plants creates continuity and rhythm. This is not only pleasing to the eye but also adds structure to the garden, making the whole more coherent.

Mutual support among plants

When perennials are planted in groups, they often benefit from mutual structural support. For example, in a group of 5 Echinacea (coneflowers), stems tend to lean on one another, which can help prevent wilting or flopping sometimes seen with isolated plants.

In addition to structural support, grouped plants can also protect one another against certain diseases and pests. Like common sage ( Salvia officinalis), known for its natural repellent properties.

Another form of mutual support is the complementarity of nutrient requirements. In a group of 5 plants, for example, if you have Nepetas (catmints) grown alongside Rudbeckias, the former prefer well-drained soil while the latter are undemanding about soil quality. This can help create balance, reducing the risk of nutrient deficiencies in the soil.

Ease of maintenance

Grouping plants with similar needs makes maintenance much easier. You can save time on watering or soil fertilisation. In addition, it allows you to focus effort on a specific area, which can save time and energy.

Space optimisation

Planting in groups also allows better use of available space. Imagine a group of 9 Hostas in a shaded part of the garden. Not only does this group create a visually attractive effect, but it also efficiently fills a space that might otherwise remain unused or be cluttered with less suitable plants.

How to choose the right combinations of perennials

The key to success in a perennial garden lies largely in choosing the right combinations. Here are some tips to get those groupings right :

Consider specific requirements

When selecting plants to form a group, it is crucial to take into account their water, light and nutrient requirements. For example, the hardy geranium and Campanula persicifolia complement each other well, as both prefer well-drained soil and moderate sunlight.

Play with heights and textures

Vary heights and textures to create a visually interesting landscape. For example, a group made up of five ornamental grasses at the back, Monardas in the middle and pansies at the front can provide visual depth and complexity.

Think about the seasons

Choose plants that will flower at different times to extend the period of interest in your garden. For example, a combination of Crocosmia bulbs for summer, asters for autumn and bergenias for spring will ensure a colourful display for almost the whole year.

Examples of successful combinations

For an English garden

Create a cottage-garden atmosphere by combining 3 superb English roses ‘Winchester Cathedral’, 5 plants of Foxgloves ‘Illumination Raspberry’, and 7 splendid Campanula persicifolia (ideally, mix white-flowering and blue-flowering varieties). The roses produce delicately scented blooms and contrast beautifully with the pink foxgloves, all set off by the blue of the bellflowers. This combination is perfect in full sun, notably in regions north of the Loire.

English rose ‘Winchester Cathedral’, Foxglove ‘Illumination Raspberry’, Campanula persicifolia

For a Mediterranean or dry garden

Evoke sun-drenched Provençal landscapes with 3 plants of Lavender ‘Hidcote’ for their fragrance, 7 Creeping thyme ‘Doone Valley’ to vary levels, and 5 handsome Sage ‘Berggarten’ for their grey‑green foliage. This fragrant combination is ideal for Mediterranean or Atlantic regions and suits gardens in full sun.

Lavender ‘Hidcote’, Creeping thyme ‘Doone Valley’, Sage ‘Berggarten’

For a country garden

Create a bucolic feel by combining 3 tall Echinaceas ‘Magnus’, 7 plants of Rudbeckias ‘Goldsturm’, and 5 ornamental grasses Calamagrostis ‘Karl Foerster’. The pink Echinaceas and golden Rudbeckias attract butterflies, adding a wild note to the garden. The grasses bring movement and height with their slim, airy flower stems. This mix is ideal for sites in full sun to partial shade and suits almost all regions of France.

Echinaceas ‘Magnus’, Rudbeckias ‘Goldsturm’ and Calamagrostis ‘Karl Foerster’

For a shade garden

Create a peaceful, verdant space by combining 5 Hostas ‘Francee’ for their large dark‑green leaves edged in white, with 3 handsome Ferns ‘Lady in Red’ and their reddish stems. Add a little brightness with winter flowering from 3 Helleborus niger. This composition is ideal for regions north of the Loire, in shade or partial shade.

Hostas ‘Francee’, Ferns ‘Lady in Red’, Helleborus niger

For a long-flowering garden

Ensure an (almost) continuous floral display by combining 3 Hardy geraniums ‘Rozanne’, 7 striking Astilbes ‘Fanal’, and 5 plants of Nepetas ‘Cat’s Pajamas’. The geraniums will flower throughout summer and provide a lovely contrast with the red plumes of the Astilbes. Nepetas extend the season with spikes of small blue flowers from spring through autumn. This combination is well suited to sunny gardens and to most regions, except the driest areas.

Hardy geraniums ‘Rozanne’, Astilbes ‘Fanal’, Nepetas ‘Cat’s Pajamas’