Landscaping a Sloping Garden in Geneva: Guide

Landscaping a sloping garden is first about controlling water and stabilising the soil, and only then about designing the spaces. A well-handled slope is cut into levels, held back by walls, gabions or planting, and crossed by steps and paths. Here is the approach, step by step, adapted to the terrain of the canton of Geneva.

Read the land before you design

Before drawing any plan, observe the land at different times of the year. A slope is understood by watching where the water runs, where it collects and where the soil moves.

What to note:

The gradient: a gentle one allows simple planting and a few levels; a steep one calls for retaining structures.
The orientation: a south-facing slope dries out quickly and gets hot, while a north-facing slope stays damp and cool.
The soil: sandy soil drains well but erodes; clay soil holds water and becomes heavy and slippery after rain.
The water flows: signs of gullying, waterlogged areas at the foot of the slope, water coming from roofs, access roads or neighbouring land.
Existing trees and roots: they help hold the ground and should not be removed lightly.
Access: on a sloping site, getting machinery and materials in affects both the method and the cost.

A landscape gardener carries out this assessment on site; it avoids building a structure in the wrong place.

Managing water and drainage

Water is the first enemy of a slope. At the surface it carries the soil away and, at depth, it pushes against walls and weakens backfill. It must therefore be collected and guided before anything else is built.

The usual principles:

Slow down runoff by breaking the slope with levels, channels or planted banks.
Collect the water upslope of the landscaped area, rather than letting it cross the garden.
Drain behind retaining walls, with a layer of gravel and a drain, to avoid water pressure.
Discharge to a suitable outlet, without shifting the problem onto a neighbour or the road.

On clay soil, this work matters even more: water infiltrates poorly, the soil swells when saturated and cracks in dry spells. Drainage work should never be neglected.

Holding the soil: walls, gabions, levels

When a slope is too steep to be simply planted, it is cut into horizontal levels held by structures.

Solution	Advantage	Good to know
Stone or concrete wall	Very durable, neat appearance	Foundations and drainage are essential
Gabion	Water-permeable, adapts to the terrain, built in stages	The filling and the construction determine how well it holds
Planted bank	Natural look, little construction	Suited to moderate slopes only
Edging and timber sleepers	Light solution for small changes in level	Limited in height and in the thrust it can take

Gabions and retaining walls are widely used on slopes: their structure lets water through, which limits the pressure behind the wall.

The levels created by these walls provide flat surfaces: a timber or stone terrace, a dining area, a vegetable patch or a lawn. A few well-proportioned levels are better than many small steps in the ground.

For a major wall carrying a load (a road, a building, a great height of earth), the calculation is a job for an engineer. A landscape gardener can recognise this situation and point you in the right direction. In addition, walls and earthworks may require a building permit: check with your commune before starting.

Steps and paths

A slope must remain usable in every season. Steps and paths link the levels; their route rarely follows the line of steepest descent, which becomes slippery and encourages runoff.

Favour zigzag paths or diagonal routes to ease the climb.
Plan regular steps with a non-slip surface (textured stone, treated timber, rough paving slabs).
Add a handrail and discreet lighting where needed.
Keep surfaces permeable where possible (stabilised gravel, grass joints) so that water can soak in.

If elderly people or people with reduced mobility use the garden, a ramp or a gently sloping path is better than steps.

Planting to hold the soil

Roots remain the best protection against erosion. A bare slope deteriorates quickly; a covered slope stabilises with the seasons.

Ground cover (ivy, periwinkle, perennial geranium, creeping cotoneaster): it protects the surface and limits weeds.
Strong-rooted shrubs: they anchor the soil at depth and give structure to banks.
Grasses: their dense root system holds soil well and withstands drought.
Lawn: best kept for gentle slopes, as mowing becomes difficult and risky on steep ground.

Preferably plant in autumn or early spring and mulch the surface, so that young plants establish without the soil washing away at every shower. On a steep slope, fascines, biodegradable geotextiles or fixed mulch protect the soil while the vegetation takes hold.

Automatic irrigation deserves zone-by-zone settings: on a slope, watering too fast runs off instead of soaking in. Short, repeated applications work better, with drip irrigation for beds. Our guide to watering during a drought explains these settings in detail.

In Geneva: what changes

The canton has many sloping sites: the hillsides of the left bank, the heights of Pregny, the Mandement, the banks of the Arve. Several local factors guide the choices.

Clay soils: common in the canton, they hold water and increase the thrust on walls. Drainage is the priority there.
Dry summers: south-facing slopes dry out quickly. Suitable plants and zone-by-zone watering are preferable.
The bise and the Lake Geneva climate: the wind dries out banks and damages young plantings; robust species and good anchoring are essential.
Rules to check: walls, earthworks and backfill may require a building permit; the commune is the body to contact.

You will find local pointers on our pages for Cologny, Pregny-Chambésy or Satigny. For an overall project, see also landscape design.

Calling in a landscape gardener

A sloping site cannot be priced remotely: it has to be seen. A landscape gardener visits, observes the water flows, the soil and the access, then proposes a suitable solution. Through request a quote, you describe your project; a qualified professional gets back to you within 24 hours for a site visit and a free, no-obligation quote. To compare offers, our guide to choosing a landscape gardener will help.

Frequently asked questions

Does every sloping garden need a retaining wall?

No. On a moderate slope, a bank planted with ground cover and shrubs is often enough. A wall becomes useful when the slope is steep, when you want to create a flat surface or when the soil risks sliding.

Which is better, a wall or a gabion?

It depends on the terrain and the intended use. A gabion lets water through and is built in stages; a solid wall looks smoother but needs careful drainage. A site visit settles the question.

Do I need a permit to build a wall or carry out earthworks?

You may, depending on the height, the location and the scale of the work. Check with your commune before starting. For a major wall, an engineer may also be needed.

Which plants should I choose to hold a slope?

Ground cover, deep-rooted shrubs and grasses are the most effective. Choose species suited to the exposure and the soil, and mulch after planting to protect the soil while the roots establish.

How do I water a slope without runoff?

Water by zone, with short, repeated applications rather than all at once. Drip irrigation suits beds well. This gives the water time to soak in instead of running down the site.