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

Why these numbers?

When planting in groups, we 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. Then, these groups of plants, for example three lavenders side by side, create a visual mass that has more impact than if these plants were isolated. The grouping gives the illusion of abundance and density, qualities sought in a well-designed garden.

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

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

A detailed look at magic numbers and their specific uses

Three: the power of the trio

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 provides visual unity while leaving enough space for each plant to grow. Moreover, three plants attract the eye more than two, without giving an impression of crowding or disorder.

Five for balance

Five is the ideal number for those seeking to create a more complex visual balance. For example, five peonies planted in a staggered arrangement. This arrangement provides both structure and depth to the garden. Moreover, five plants also allow playing with different heights, for example in contrast 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 instance, combine three pink Astilbes with four white-flowered Astilbes (seven in total) for a play of colours and textures.

The charm of nine for large borders

The number nine is generally reserved for large spaces or for gardeners who look to emphasise a plant in a bold way. Take, for example: a group of nine irises can serve as a focal point in a large garden, drawing the eye from afar. The number 9 also allows greater diversity, offering the opportunity to combine several subgroups of three different plants (for example, three varieties of three irises) to create a patchwork effect.

The benefits of planting in groups

The aesthetic impact

Aesthetic appeal is one of the main reasons many gardeners opt for group planting.

Example: Let us take a group of 5 Hemerocallis (daylilies), placed behind a group of 3 Hydrangeas. This display creates visual harmony, where the Hydrangeas provide volume and a certain roundness, while Hemerocallis (daylilies) add height and contrast with their long stems and trumpet-shaped flowers. This display plays on differences in shape, colour and texture to create a display that is more captivating than a simple line-up of plants.

Another important point is the effect of repetition. Rather than scattering the same type of plant at random across the garden, grouping an odd number of these plants creates continuity and rhythm. This is not only pleasing to the eye, but it also adds a certain structure to the garden, making the whole more cohesive.

Mutual support among plants

When perennials are planted in groups, they often benefit from mutual structural support. For example, in a group of 5 Echinaceas, the stems tend to lean on one another, which can help to prevent wilting or drooping that is sometimes observed in isolated plants.

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

Another form of mutual support is the complementarity of nutrient needs. In a group of five plants, for example Nepetas (catnip) paired with Rudbeckias, the former prefer well-drained soil while the latter are not particular about soil quality. This can help create balance, reducing the risk of nutrient deficiencies in the soil.

Low maintenance

Grouping plants with similar needs greatly simplifies maintenance. You can therefore save time on watering or soil fertilisation. Moreover, it allows you to concentrate your efforts on a specific area, which can save time and energy.

Space optimisation

Group planting also enables better use of available space. Imagine a group of 9 Hostas in a shaded area of the garden. Not only does this group create a visually appealing effect, but it also helps fill space that might otherwise lie unused or become crowded with less well-suited plants.

How to choose the right combinations of perennials?

The key to a successful perennial garden lies largely in choosing the right combinations. Here are a few tips to get this arrangement right:

Take account of specific needs

When selecting plants to form a group, it is crucial to consider their needs for water, light and nutrients. For example, the hardy geranium and the Campanula persicifolia complement each other well, as both prefer a well-drained soil and moderate light.

Play with heights and textures

Vary heights and textures to create a visually interesting landscape. An example: a group formed of 5 ornamental grasses for the back, Monarda for the middle and Pansies for the front can offer depth and visual complexity.

Think about the seasons

Choose plants that will bloom at different times to extend the period of interest in your garden. Such as a combination of Crocosmia bulbs for summer, of Asters for autumn and of Bergenias for spring, thereby ensuring a colourful display nearly all year round.

Examples of successful combinations

For an English garden

Create an atmosphere worthy of an English cottage by pairing three sublime English roses ‘Winchester Cathedral’, five Digitalis ‘Illumination Raspberry’, and seven admirable Campanula persicifolia(ideally, mix the white-flowered variety with those that bloom blue). The roses produce delicately scented flowers and contrast nicely with the pink blooms of the foxgloves, the whole heightened by the blue of the campanula. This combination is perfect in a sunny display, particularly in regions north of the Loire.

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

For a mediterranean  or dry garden

Évoquez les paysages ensoleillés de la Provence avec 3 plants de Lavande ‘Hidcote’ pour leur parfum, 7 Thymus creepeing ‘Doone Valley’ pour jouer sur les hauteurs, et 5 belles Sage ‘Berggarten’ pour leurs feuillages gris-vert. Cette belle association de senteurs est idéale pour les régions méditerranéennes ou atlantiques et convient parfaitement aux jardins en plein soleil.

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

Pour un jardin champêtre

Créez une ambiance bucolique en associant 3 grandes Echinaceas ‘Magnus’, 7 Rudbeckias ‘Goldsturm’, and 5 grasses Calamagrostis ‘Karl Foerster’. The pink-flowered echinaceas and golden rudbeckias attract butterflies, adding a wild touch to your garden. The grasses bring movement and height with their slender, airy flower stems. This mix is perfect for a sunny to partly shaded display and suits almost all regions, except the driest.

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

Pour un jardin d’ombre

Créez un espace paisible et verdoyant en associant 5 Hostas ‘Francee’ pour leurs grandes feuilles vert foncé, bordées de blanc, avec 3 belles Ferns ‘Lady in Red’ et leurs tiges rougeâtres. Ajoutez un peu de lumière avec la floraison hivernale de 3 Hellebores niger. Cette composition est idéale pour les régions au nord de la Loire, à l’ombre ou à la mi-ombre.

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

Pour un jardin à longue floraison

Assurez un spectacle floral (presque) en continu en associant 3 Hardy geraniums ‘Rozanne’, 7 surprenantes d’Astilbes ‘Fanal’, et 5 plants de Nepetas ‘Cat’s Pajamas’. The hardy geraniums will provide flowering throughout the summer and offer a nice contrast with the red plumes of the Astilbes. Nepetas prolong the flowering with their spikes of small blue flowers from spring to autumn. This combination is well suited to sunny gardens and suits most regions, except the driest.

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