Horticulture Magazine

8 Tips For Planting And Gardening On A Slope

landscaped garden slope with rocks and waterfall

Gardening on a slope doesn’t have to be the nightmare it is sometimes envisaged as being.

An incline can certainly bring some challenges, but these are not insurmountable and also provides some creative opportunities that you wouldn’t have compared to a flat area.

Some of the most beautiful and creative gardens are built on slopes, including the Lost Gardens of Heligan in Cornwall. Sloping gardens can provide great vantage points which would not be possible on a level garden and views either from or towards the house.

Whether your plants struggle to thrive or the gradient is such that water runs down the slope rather than seeping in to nourish the plants, don’t worry as we’ll cover how these challenges can be overcome and how your garden on a slope can thrive.

1. Planning

Whether you have a small sloping border or an acre or two of sloping garden, planning is essential. It is so worth taking the time to assess the site and plan, before getting the spade out or hiring a landscaper.

The site’s gradient, aspect and drainage will have a huge deciding factor on what can be grown and how. From a small border that can be levelled by a wooden sleeper to a garden requiring heavily engineered retaining walls, assessing the requirements and planning accordingly could not only help avoid costly pitfalls, but help you create wonderful and usable space.

Steep slate steps with some conifers and rhododendron
Steep slate steps with some conifers and rhododendron

Gardening on a large slope has the potential to exhaust even the fittest of us, but with careful thought this can be minimised. Lower maintenance areas can be placed furthest from the house and more intensive areas such as vegetable patches nearest, lessening trips up and down.

Shallow meandering paths are far easier on the legs, especially with a wheelbarrow in hand and offer the chance to take in hidden parts of the garden.

Safety must be considered, especially where children and pets are present. Along with the safe use of any garden machinery on a slope.

Irrigation is key and a well thought through drainage plan, irrigation system or tap placements can make all the difference to the planting scheme and the garden as a whole.

2. Gradients

Maybe it is just one border that slopes a little or the whole of your property and garden. Either way it is important to work out the gradient of the slope in order to understand what you are working with and the potential solutions available.

It is possible to work out the gradient of the slope with a tape measure and some relatively simple math, or alternatively a professional gardener or landscaper would be able to work this out for you.

This gradient will help determine your options for planting, access and for maintenance. For example, water will run off on an incline of 1:2 and not be able to penetrate down to the plants’ roots and most domestic mowers will advise against use on a slope of more than 10% or 1:5. When it comes to the actual planting it is generally recognised that a 1:3 slope is the maximum allowable to give the plants a good chance.

A slope of 1:3 can be successfully planted with certain plants, shrubs and trees, but if you are dealing with a steeper incline a more structural approach would be needed.

Before you start, take a look at what is already there and make a note of what is doing well and what is struggling. Does the rain simply run off down the slope eroding the soil as it goes or are there any trees and shrubs that are helping bind the slope together or creating shade and dry areas?

3. Terracing

Terracing usually includes one or more new levels of varying height as needed for the slope in question and can be made from brick, concrete block, wooden sleepers or rock filled gabions. The structural and drainage requirements will often dictate the most suitable material to use and often be reinforced with steel rebar if required.

wooden poles used as palisades on a steep slope
Wooden poles used as palisades

In all but the smallest borders, the retaining walls will be holding back considerable weight, requiring professional construction and consultation with a structural engineer.

When considering terracing as an option it is also important to bear in mind the design of steps or pathways to access the higher levels and whether these will need extra grip or handrails to keep them safe. Lugging gardening tools, children’s play equipment or even food for the BBQ is no fun if the steps are steep or paths slippery.

If the garden is being professionally landscaped do consider the options of installing an irrigation system or at the least a hose tap at the end furthest from the house to avoid trying to carry endless watering cans up and down. 

Terracing, especially on a large scale is not cheap, but maybe the only option to form level areas for planting and seating areas. Even though potentially costly, terracing a garden can be incredibly creative and allow for exciting design ideas such as sunken seating areas and eye level planting schemes.

4. Drainage and planting

If the slope does not require terracing it is still important to think carefully about the drainage and planting. Typically, the area at the top of the slope will be drier than the bottom where it will drain down to. Water can collect behind the retaining walls, especially if they are impervious, leading to added pressure issues. This can be potentially be addressed by incorporating gravel drainage behind the wall and weep holes in the wall to allow water to drain out.

If soil erosion is a problem, then ground cover plants and deeper rooted or mat forming plants will help deflect the rainfall, bind the soil together and minimise soil run off.

Even creating a mini terrace around each plant or shrub can help and is easily achievable with a few bricks pushed into the soil just below the plant. This will allow the water to settle around the plant and not wash away the soil and nutrients.

a colourful floral display in public gardens
Colourful floral displays are still possible on sloped areas!

Mulching the planted area will help limit any erosion as well as retaining moisture. Larger mulch such as bark or straw is less likely to be washed away than finer ones, but will still allow water to reach the ground.

5. Mat forming plants

Weeding a sloping border is not easy. Mat forming and ground cover plants will block the light to the soil below and thus hopefully reduce the need for weeding. The choice of plants will be dictated by the garden style, aspect and drainage requirements but ground cover plants include; Ajuga reptans (bugle), Alchemilla mollis (lady’s mantle) and Vinca minor (periwinkle). Beware of using vinca though as it can become invasive.

6. Deep root plants

Deeper rooted plants tend to stabilise and hold the soil together and thus reduce erosion. These can include trees, shrubs and perennials. Shrubs can work well on a slope putting roots deep into the soil and requiring relatively low maintenance. Shrubs could include forsythia, Cotoneaster horizontalis (rockspray) or Ceanothus (Californian lilac).

Sun loving prairie plants and shade loving ferns can also do well on a slope depending on the aspect.

7. Rock gardens

Rock gardens or rockeries can be a great way of adding interest and structure to a sloping border or garden. Suitable for alpine plants, a rockery requires a sunny site and so needs to be situated away from shading trees.

Using existing rocks and boulders or using locally sourced reclaimed materials will help achieve the natural style.

rock steps leading upwards
These rock steps act as a focal point of the garden

Alpine plants can be spring, summer or winter flowering injecting colour into the sloped area in a naturalistic style. They require a free draining soil mix and can be suited to both sun and partial shade. Alpines are naturally hardy coming from mountainous regions and suitable for most climates here in the UK.

8. Scree gardens

Scree gardens are taken from the naturally forming scree slopes on mountains. Scree is essentially an accumulation of small stones or rock fragments and as with rock gardens need excellent drainage.  Scree gardens are created on a base layer of coarser rocks or rubble, covered with a free draining mix of gravel and soil and finally a layer of limestone or gravel chippings.

Scree planting can provide a creative opportunity and can include spring and summer flowering plants, often low growing and not found in a typical garden border. Common examples of scree plants and bulbs include Anemone blanda, Campanula alpina and Aster alpinus.

cacti in a scree garden with white gravel
Cacti in a scree garden

Slopes in a garden offer can offer some fantastic potential, so don’t let gardening on a slope put you off, as with careful planning and consideration it can offer some creative opportunities that an otherwise level area might not.

If this all seems like too much, you might also be interested in tips for levelling a sloped garden.

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