You may want a Mediterranean-style garden or a dry garden for a technical reason, such as meeting the cultivation requirements of particular plants or adapting to particular climatic conditions.
The problems we have been experiencing with our “good old temperate climate” also explain the interest in gravel gardens.
As a first step, we will look at the advantages of this type of garden, how best to prepare the soil, how to design and lay out the garden, and how to choose the plants.
Above. This photo of a rockery in a trough summarizes the benefits of growing plants on gravel: – a mineral mulch, which regulates humidity and sets off the plants.
A gravel garden may be the result of a landscaping decision.
A mineral mulch: gravel prevents leaching of the soil by rainwater and restricts weed growth.
Seeds in the soil cannot germinate. Gravel provides drainage which is an important factor for success with growing many plants as it indirectly increases resistance to the cold. Mediterranean, maritime and alpine plants like this type of environment. A dry collar and well-ventilated roots! In the summertime, gravel prevents the soil from drying out.
A condensation effect at dawn helps keep the base of the plants cool. White or light-coloured gravel reflects the light, which means less heat!
Finally, gravel lets you design great gardens as it enhances the forms and foliage of the plants.
And in the winter, the garden seems brighter.
Can I cover a geotextile with gravel? This is a technical solution to reduce weed growth.
At the nursery we prefer not to use it, so that the seedlings and self-sown plants are free to grow.
It’s quick to hand weed a gravel garden, as it’s easy to pull out young weeds by the collar.
We only have one enemy (the sworn foe of any gardener): bindweed!
The bushy and the upright: the happy marriage of Verbascum olympicum and Stipa tenuifolia
In the foreground: Euphorbia characias sp Wulfeni. In the background: Sedum x Matrona and Erigeron karvinskianus.
As with all beds for perennials and grasses, the preparation of the soil is an important phase on which the success of the garden depends:
Clearing and weeding a gravel garden
For small areas, detailed weeding can be done by hand. For larger areas, we recommend installing woven plastic sheeting that you can easily find in agricultural supply stores or garden centres.
The woven plastic allows water and air to get through. The soil thus continues to live, unlike with soil solarization where the soil is quickly disinfected by heating.
The sheeting is secured on the sides and must remain in place for a minimum of three months. So the ideal time to lay the sheeting is at the beginning of spring. (We strongly discourage the use of chemical weed killers over large areas as they do have an impact on the environment.)
Tillage and amendments for the gravel garden
There is a pleasant surprise after a few months, when you see that the soil is clean and soft. Only some dock and bindweed remain which can be easily removed. Finally, the soil can be dug over to prepare for the planting. At this point we must not forget to spread some compost (3 kg/m²), Patenkali for additional potash (3 kg/100 m²) and extra lime if necessary to correct the soil pH.
Laying out the bed
Be generous with the space and the volumes. Define perspectives and focal points. A gravel garden is a free space in which most of the species planted will tend to re-seed themselves. It’s best to choose a spot with a sunny, clear exposure.
You should avoid siting the garden near stands of deciduous trees. Make sure the pathways are wide as the edges of paths/beds are not too definite and they will be quickly become overgrown. Bear in mind that you will need space for maintenance and to rake the gravel. The edges between gravel and earth and gravel and lawn should be restrained (paving stones, railway sleepers, etc.).
It is important to enhance the shape of each plant. Make sure that you considerably increase planting distances and take care to choose well-structured plants, e.g. Euphorbia, Sedum, Agave, Phormium, Grasses, Eryngium.
It is a good idea to create elevation by raising the beds by about 10 to 30 cm. Terraces and frequently-used paths (for lawn-mowers, push-chairs, etc.) should be paved for safety and comfort.
Choice of plants
Dry, sunny exposure. A well-drained soil, not too acidic and rather poor. Work on contrasting shapes: upright / bushy, defined / diffuse. These are two ideas for choosing plants.
A few examples of perennials and bulbs that have an upright habit: Allium hollandicum, Allium sphaerocephalum, Asphodeline lutea, Berbena bonariensis, Dierama pulcherrimum, Eryngium giganteum, Gaura lindheimeri, Kniphofia, Lychnis coronaria, Nectaroscordum siculum, Onopordium acanthium, Phlomis tuberosa, Verbascum bombyciferum.
A few examples of perennials and bulbs that have a bushy habit: Achillea ‘Coronation Gold’, Achillea ‘Terracotta’, Achillea ‘Safran’, Allium tuberosum, Allium flavum, Anthemis ‘EC Buxton’, Artemisia camphorata, Artemisia ‘Valerie Finnis’, Bergenia sp., Diascia sp., Euphorbia characias, Euphorbia polychroma, Helleborus sp., Festuca glauca, Origanum sp., lavender sp., Salvia officinalis sp., Santoline sp., Sedum ‘Autumn Joy’, Sedum x Matrona, Silene, Thymus sp.
Grasses: Agropyron magellanicum, Calamagrostis ‘Karl Foerster’, Miscanthus sp., Molinea ‘Transparent’, Stipa arundinacea, Stipa gigantea, Stipa tenuifolia, Festuca, Sesleria, Corynephorus.
Some shrubs (to be placed at the back or in the middle of the bed): Abutilon, Buddleja, Cistus sp., Cotoneaster, Lavatera sp., Tamarix, Rosa glauca, Melianthus major, Ligustrum, Rhus.
Ground cover and edging plants: Acaena sp., Allium tuberosum, Antennaria dioicia ‘Rosea’, Diascia sp., Euphorbia myrsinites, Euphorbia rigida, Fritillaria sp., Primula auricula, Saponaria sp., Saxifraga, Sedum cauticola, Sedum ‘Ruby Glow’, Sempervivum, Sisyrinchium, Thymus x citriodorus, Thymus serpyllum sp., Thymus longicaulis, Thymus praecox ‘Minor’, Veronica sp.
Gravel is expensive to transport. It is best to choose the nearest quarry, but it is worth visiting several to check the quality of the stone. Choose a particle size of between 5 and 10 mm. Too thin or too thick makes walking difficult. Choose a light-coloured gravel, yellow or pale grey. Avoid white which shows the dirt. Gravel has a density of 1.8, so a cubic metre weighs 1.8 tonnes. As you need a depth of 3 cm, you might have a significant weight of gravel to transport. You can use pebbles or stones with gravel to mark a transition, a step or the edge of a terrace.
Cleaning and weeding Gravel should be kept clean and the plants tidied and trimmed regularly. It’s up to you to deal with the weeds!
It’s a good idea to leave the self-seeded plants where they are if they fit in. For instance, a Stipa growing in the middle of a path may be worth keeping. However, you need to be merciless with the weeds, but you will notice that they are easy to pull up.
Apply weed-killer in the beds with a paint-brush and with a spray boom on the paths. Overall, this will lighten your work-load as there will be less weeding and no hoeing. And the results are always rewarding.
If you want to design and plant your own gravel garden
For more information:
Rock Garden Plants by Christopher Grey-Wilson and Linden Hawthorne.
Gravel Garden by Beth Chatto, Drougth resistant Planting by Beth Chatto and Steven Wooster