Creating an alpine rockery

What is an alpine rock garden?

An alpine rock garden aims to recreate artificially certain landscapes that can be encountered in the mountains, where different plants grow on steep, rock-strewn ground. In this kind of environment, plants are generally well exposed to sunlight and water they receive from precipitation does not pool around roots or the collar (junction between above- and below-ground parts). Moreover, the rocks present store daytime heat to release it at night, thus creating a favourable microclimate. They also provide a degree of coolness (water evaporates more slowly beneath stones) from which plants can benefit without risk of overwatering.

Creating a rock garden in your garden thus allows some of these conditions to be reproduced and enables cultivation of plants that might not otherwise establish without a little helping hand. Indeed, high humidity or heavy soil, especially when combined with prolonged cold temperatures, can suffocate roots of alpine plants and may be fatal.

A natural mountain landscape: a slope, rocky soil, alpine plants typical of this environment

How to create a rockery?

• To mimic Nature as closely as possible, it is essential to work on ground that offers a minimum gradient. This way, water drains to the bottom of your ‘slope’ and plants never become waterlogged. If your site is already sloping, make the most of it! If not, create an artificial slope by forming a mound. This can be done by reserving part of the soil excavated during house construction for this use. On an existing plot you can always have topsoil delivered. Rest assured, there is no need to create an Everest at home! A total gradient of about 60 cm every 2 metres is more than sufficient. If the slope is steeper, that is not a problem, provided you stabilise the whole with rocks. Rather than shaping a regular slope, try to create tiers and offsets, with some sections rising slightly from time to time, as is the case in natural environments.
  

  Slope diagram, sketch © Jean-Christophe Aumont

• Once your slope is in place, you need to add the mineral elements to your rockery. Choose rocks of different sizes, some large enough both to create the scene and to hold the soil. Prioritise local stones for better integration with the surrounding landscape and buildings, and to limit ecological footprint. Arrange your rocks in a deliberately informal, as-natural-as-possible way. For the largest stones, dig trenches so their base is buried to at least one-third, or even two-thirds if they are very large, to guarantee stability. These stones also help to retain the soil of your bed and prevent the substrate from being washed down to the bottom by rainfall. For aesthetic interest, alternate larger rocks with more modest ones. Smaller stones and pebbles also serve to mimic the scree that forms on mountain slopes.
• When designing, plan for future maintenance. You must be able to access your bed. Depending on the size, slope and shape of your rockery, consider adding paths, stepping stones or steps to make maintenance easier.
• The slope provides natural drainage, but increase it by adding a good proportion of draining material to the soil, such as gravel of various sizes and coarse sand. Alpine plants grow in poor soil, so adding organic matter is rarely necessary.

The aim is to create a significant but irregular slope and to place rocks of varying sizes

Which exposure should I choose?

Alpine plants prefer open, well-exposed sites. In regions with very hot, very dry summers, a west-facing aspect may be preferable. Elsewhere, south-west, or even south, may be suitable.

How to plant a rockery?

Rock garden planting generally follows same principles as a conventional border.

1. Ensure soil has been well weeded.

2. For shrubs, which require larger planting holes, use a spade and dig a hole approximately twice the size of the pot, if possible. A small trowel is sufficient to create planting holes for perennials and bulbs (editor’s note: there are special narrow rockery trowels). Proceed in same way as for shrubs, adjusting proportions accordingly.

3. If necessary, add some drainage material to soil.

4. After soaking your shrub in a bucket of water to saturate substrate, remove from pot and position it at centre of hole.

5. Fill in with remaining substrate and firm lightly with fist.

6. Water plantings thoroughly with a gentle spray, but do so in several small waterings.

7. Once planting is complete, spread a layer of gravel over soil surface, around plants and rocks. This layer both insulates against cold and prevents plant collars from being in direct contact with moisture, while also providing an attractive finish.

Planting an alpine rock garden is similar to planting a border once layout is established

Which plants for an alpine rockery?

Different plants can be used to vegetate such an installation, from the tallest, upright specimens to those with a low, creeping habit. Take care, however, to match plant size to the scale of your composition to preserve a good balance. The larger the rockery, the more you can allow yourself to include larger-growing subjects.

• As a rule, alpine shrubs are often evergreen and are largely represented by conifers, which helps them cope better with climatic hazards (cold, wind, snow…).
• With perennials, play with flowering periods but also consider foliage, which brings colour for a longer period, especially evergreen foliage that brightens your rockery throughout the year.
• Finally, don’t forget early-flowering bulbs that kick off the season, very early for some, and a few ornamental grasses for their lightness.

Evergreen shrubs

Among shrubs and undershrubs with evergreen foliage that you can use in an alpine rockery consider, for example, heathers (Erica), cotoneasters or black crowberry. It is difficult, even impossible, to imagine such a scheme without rockery conifers, which combine slow growth, modest dimensions and sometimes surprising seasonal colours. Cryptomeria, cypress, spruce, junipers, pines or thujas are just a few examples of shrubs with upright, globose or even prostrate habits, allowing attractive contrasts of form and silhouette. Their foliage comes in various greens but also in bright yellows, deep blues or surprising oranges that never go unnoticed.

Dwarf conifers are essential in a rockery

Deciduous shrubs

Deciduous shrubs allow you to vary the palette and complete scenes with joyful flowers or fruiting displays, heady scents or interesting foliage. Among those suitable for a rockery, consider, for example, barberries, caryopteris, coronillas, brooms or potentillas.

Tall perennials

Alpine perennials exceeding one metre are not numerous, but some can create interesting vertical accents, such as summer-flowering willowherbs, ornamental eryngiums with striking forms or yellow gentian, whose bright blooms require patience.

Low perennials, cushion or carpeting types

Many rockery perennials adopt a low habit, forming dense cushions or mats that follow the shape of the terrain. Ideal for the foreground, they also set off their taller neighbours. For example, the very popular alyssum, aubrieta, iberis and some erigerons, without forgetting Alpine gentian, moss phlox, Alpine aster, sagina and of course the emblematic edelweiss.

Moss phlox and some saxifrages make excellent alpine rockery plants

Mediterranean and desert perennials

Nothing prevents you from stepping off the beaten (mountain) track and including plants that are not strictly alpine but, like them, prefer well-drained soil and plenty of sun. Sempervivum, cacti, agave, aloe, crassula, delosperma, echeveria, mangave and friends add a touch of originality and exoticism, the limit being determined by hardiness in your area.

A rockery incorporating desert and Mediterranean plants

Bulbs

It’s easy to tuck in groups of bulbs that awaken late winter and spring with their sparkling colours. Easy to grow, reliably returning each year and sometimes naturalising, they guarantee an early-seasonly floriferous rockery. Crocus, Iris pumila and Iris reticulata, Ipheion, botanical daffodils, snowdrops, Scilla ‘Tubergeniana’ or botanical tulips… all are sure to charm us!

Grasses

Grasses provide suppleness and movement to a rockery. As alpine plants are often low, stay in that spirit by choosing, for example, blue oat grass, fescues or feather grass.

Small grasses such as cushion fescues make excellent rockery subjects

Maintaining a rockery

Maintaining a rockery is not complicated, especially as plants grow and cover the soil.

• An initial weeding before planting is, of course, essential but must be continued over time, when necessary, so that weeds do not compete with your plants and to keep the composition looking neat.
• You should water your plants immediately after planting but you must also ensure the soil does not dry out too much in the first months, while your plants become established. Plants shown here tolerate dry conditions well, but the climate changes we now experience each year may sometimes force the gardener to water from time to time during prolonged dry spells. Water with a fine spray to avoid displacing surface gravel or dislodging your plants.
• Remove faded flowers when necessary and cut back any dry parts that have become unsightly.
• After a few years (about 3 to 4 on average), some plants benefit from being lifted to be divided and thus rejuvenated.
• Some tender plants may require winter protection in the form of a transparent polycarbonate sheet. This, held in place by stakes driven around the plant, lets light through but prevents precipitation from reaching the crown, thereby protecting it from rot.

Further reading...

• Discover our wide range of alpine perennials!
• Find further inspiration with our rockery perennials.
• Make the most of the great diversity of rockery conifers!