Sustainable Designs for Sloping Sites

One of the more common challenges in Scottish gardens is sloping ground. Writing this article, the irony is staring me in the face: while I was born in Holland, a country as flat as the proverbial pancake, steep slopes are now a big part of my daily job. 

To a designer, a sloping site can have lots of potential for instant interest. At the drawing table, all elevations and slopes can be played with until things work well. When creating a sustainable garden, the solutions have to embrace even more elements than in a conventional landscape design. The time spent considering materials, soil, and plants beforehand though is worth it – caring for our environment whilst creating beautiful gardens is the future.

Sloping, rocky gardens often come with the most amazing scenery.

When I started my career in horticulture, I worked alongside an established landscaping team on a rather steep garden in Edinburgh city centre. My mentors told me to never forget: build up the soil rather than excavate. By terracing and levelling with top-soil, the site benefits from easier maintenance and from little soil disturbance.

The words of my mentors were still with me three years later, when I visited a client in Aberdeenshire. Their house was built on the site of an old well, into a steep slope, backed by forestry commission woodland. Behind their house was a long, sloping lawn. The family struggled mowing this site without the ride-on toppling over.

This is a simplified birds-eye view of the site when I arrived. A gently sloping lawn surrounded the back of the garden. A moon crested excavation, possibly created when building the house, had left a slope in one area of the lawn that was too steep to cut with a lawn mower. As it is facing the south-west side, the slope shaded out this side of the house.

The family wanted to create a garden that was more easy to maintain, while introducing forest garden plants. The idea of a forest garden is that you plant trees, shrubs, and herbaceous perennials that have edible elements but you do not harvest the plant completely. It is like going out to your garden to forage fruit, berries, leaves, stems, and sometimes even roots. 

Their plan was to improve things by building a tall wall and levelling the lawn at the top level. When imagining a 3 metre high wall, 35 metres long and very close to the house, all I could see was a dark, damp space with little use: not a view most people would want from their windows.

Although the high dyke would have solved the problem of the steep slope, it would have created even more shade at this side of the house. The wall would have felt large and imposing.

Compromises have to be made sometimes. Excavating means disturbing the soil as well as using heavy machinery, not the most sustainable solution as soil structure and soil life is compromised. Yet in this particular case, opening up the space and making two levels in the retaining wall would let in the sunlight. The brief was to remove the slope and create a food forest but with three active children and a rich social life, I knew the family would also benefit from more space to play, relax, and entertain. The solution we decided on required excavating some of the soil to create two levels. 

The ground level now has steps leading onto a level grassed area. The semi-circle shape creates a lovely entertaining space, with easy access from the house. The level lawn is perfect for children to play and is easy to mow. A second dyke overcomes most of the level differences but is now much further away from the house, not shading out light. The border at the top will be planted with shrubs and underplanted with tumbling plants. Both shrubs and tumblers will be edible, creating a perennial vegetable and fruit garden to forage from all year around.

The choice of material used for the retaining wall was an easy one in this case: a drystone dyke. Random stone is often piled up next to a field after ploughing, with little use for it. Creating a drystone dyke with such fieldstone means that you use natural material. Having no mortar has the added bonus of creating a habitat for a myriad of wildlife. 

On this particular site, it also meant that drainage would not be a problem, which it would have been with a solid structure. Being built on an old well, it was a wet site. If water does not drain away freely it can build up behind a wall, causing pressure that may eventually mean that the wall might break. Dry stone walls let water through freely. What it does require, however, is a lot of stone, and many hours spent by an experienced craftsman. After having completed a drystone dyking course, I appreciate just how time consuming it is to make things look beautiful. If you have a limited budget and need a lot of retaining wall, you might need to consider other options.

Work on the upper level of this long drystone dyke. Although time consuming, drystone dyking can create a sustainable eye catching feature in the garden.

If you choose to terrace a slope in your garden, there are plenty of options that are more sustainable alternatives to breeze block.

Drystone dykes and loosely placed boulders using random, uncut fieldstone are an excellent option for retaining soil sustainably. Costly in terms of labour, they do last for hundreds of years if constructed well. When using local stone, it is a thing of true beauty and naturally fits into its surroundings. 

Certified, treated wood from a local sawmill can be a great renewable option. If you can find reclaimed wood, then that is even better. At the end of its life cycle, when renewing the garden, wooden waste is biodegradable, an important consideration often forgotten. Bear in mind, however, that the life-span is limited compared to stone.

Cut stone, bound with mortar or used in a dry stone structure, is best sourced locally from quarries, reclamation yards, or local demolition sites. You can choose uniform sizes and mixed sizes. When the wall is built with mortar, consider drainage behind the walls and between the stone.

If you want to use breeze block because of the ease of construction, there are now eco-friendly alternatives such as hempcrete, timbercrete, or concrete blocks made from recycled plastic.

Re-use anything you have on site if possible. If you do have bricks, stone, or breeze block on site, re-using these rather than bringing them to landfill is a sustainable option. To construct it well and for it to work with the look you are after, you might need some imagination and a lot of time but it can work out beautifully.

When struggling with ideas on how to transform awkward slopes in eye-catching gardens, the help of a garden designer can be invaluable. Do ask your designer about sustainable options – the more we ask, the more such products will become widely used. 

In this steep and narrow garden, every centimetre counts to get the design right.

Katrina Flad runs her sustainable garden design and landscaping business frock n wellies from her home in Aberdeenshire. Passionate about the planet and all things that live on it, she wanted to make a real difference to her environment ever since she can remember. 

In this regular column, Katrina will bring you design solutions for your garden which are sustainable, practical, and beautiful. Follow Katrina at frock n wellies on Instagram and Facebook

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