Dealing With a Sloping Site with Charlie Albone

 By Charlie Albone

The topography of your garden has a huge impact on the design aesthetic of your space and one that needs careful consideration to not only look good but have useful areas and successful planting.

When it comes to creating areas on a sloping garden you can use for entertaining and relaxing creating flat spots is a practical must and for that you will need to ‘cut and fill’.  This basic landscaping principal means taking from the high spot and placing that earth in the low spot to create a flat area but it’s not as easy as just piling the dirt up and laying paving on top of that.  You will need to retain the soil either on the low, high or both sides of the cut.

Retaining Your Soil

Retaining walls can be a costly addition to the garden and for something substantial or a retaining wall on a boundary you will need to involve your local council for consent and gain engineering advice.  For small walls, a low retaining wall is something you can build yourself to gain some much-needed flat space within the garden.

Unless you have experience in laying bricks or blocks, I would steer clear of masonry walls, the footing can be complicated and you need some hands-on skill to get them level and plumb, not to mention the cost. The use of boulders can be used to retain pockets of soil that can be planted up to give you a softer more organic way of holding the soil back, although you do need some strength or a machine to manoeuvre them into position.

Timber sleepers are a lightweight, cost effective and easy to install option, and there is plenty of building advice available online.  The issue with timber sleepers is the look, it certainly doesn’t say high end and the lengths come in 2.4 or 3 meters long which can be a constraint if you are thinking of adding some curves to your spaces.

Edging a Smart Option

ShapeScaper Steel edging is the perfect option for small retaining systems in the garden as it is D.I.Y. friendly and easy to install, can be straight or curved and comes in various heights with easy joining plates so incredibly versatile as far as fitting different projects and sites.  The 150mm edging can be used as steps up in a garden space, the 390mm and 590mm high profile make excellent retaining systems with rigidity coming from concreting the pegs into the subsoil.

I’m a huge fan of using steel edging as a low retaining system, especially in a tight space, as the thickness of the steel compared to timber or block means additional space for more entertaining space or plants roots  and the maintenance free patina it gets over time only makes the finish and maturity of your garden space get better with age.

Drainage Considerations

Whatever material you select for your low retaining wall the one element you cannot scrimp on is the drainage.  The majority of failures in retaining walls come from hydrostatic pressure, this is where the water builds up behind the wall and literally pushes it over. To deal with this you will need a slotted drain (ag-pipe) behind the wall to direct the water flow around the wall.  Position this drain up against the bottom corner of the wall where it will collect the most amount of water.

It is also important to protect this drain with geo-fabric that is surrounded by aggregate, such as blue metal which is once again wrapped in geo fabric as this will prevent the drain from filling with soil over time.

Planting on a Slope

When it comes to planting up around your new retaining walls it’s important to remember the high side will have more drainage so drought tolerant plants are a must whereas the low side will now naturally hold more water (even with a fully functioning sub surface drain) giving you a more diverse choice with your plant palette.

If you have a slope and do not need a level spot for gathering and entertaining, then simply planting it up will help to retain the soil as the plant’s roots work like a web of mini anchors holding it all in place.  The rule of getting the right plants for the right spot on the slope is just as important with drought tolerant at the top, water lovers at the base and then a mix of the two or a whole new species in the middle.

If planting up a slope it is well worth installing some jute coir logs running horizontally along the slope.  These are like hessian sausages that get pegged into the slope and work by slowing the water flow and allowing it to seep into the soil beneath rather than simply running off to the base of the grade.  Being a natural material, they will degrade in time but the plants root system should be well established by the time this happens and you will get a much better success rate during establishment.

If you want a longer term option then installing ShapeScaper edging in 150mm profile will do the exact the same thing as a jute coir log but it will last much longer and look more polished whilst the plants take hold, you also then have the versatility of leaving sections of planting out to expose the edging giving you a designer look to your sloped area.