Retaining walls and garden shaping

The Sweeper

Questions for some of the landscapers among you.

I'm finally in my new house, on a block of 1230m2 so just under a third of an acre. The garden, of course, is a bloody great tatty mess of weeds, thistles, heavy clay soil and compacted earth.

We're starting off by cutting everything back to ground level, but there are constraints on time and money so I can't do precisely what I'd like to do (level it all, poison it, then rotovate it, then topsoil, then raised beds, then compact between and lay gravel or pavers between raised beds, keep a small area of lawn and so on and so forth) from the outset.

I a few questions re the front garden because I want to sort that out first. (The back garden and side gardens can be a long-term labour of love once our fences have gone up and I'm hidden from the outside world, but the front garden will always be open to the road.) The block is 23.5 metres wide and the house is a 10m setback from the road, so my front garden is basically 23.5 metres wide and 10 metres deep mostly. There's a driveway poured to the right hand side, along with a path that curves from the edge of the driveway to the front door.

The problem is none of the front garden is flat - there was a short, sharp batter at the front of the property, so you have road level, then an area of earth approximately 7 metres from road to cut, with a fall of a half a metre over it, then a drop of around 50-70cms to the level of the house - that's where the site cut happened. Because the soil is heavy clay, the cut itself is stable and forms a mini 'cliff' about three metres from the front door.

I have decided some of what I want to do - I would like a retaining wall in front of the cut - I don't think it needs to be a structural retainer as the cut is not high and the soil is standing of its own accord.

I'm in two minds whether to make the retaining wall a metre high and backfill so the front garden is level and then drops to the house, or keep it at about 70cms and backfill a little so the garden is still a slope. Then there's the question of what to make such a wall from. I want to keep some of the front garden as lawn, and some of it as flower beds, so I'm happy to plant various tumbling creeping things along the top edge that will cascade down over the wall and break up any potential monotony or ugliness.

I don't mind the rustic look, and I have access to most materials - e.g. I could buy large wooden logs, similar to old round telephone poles, and split some in half and stack them behind vertically sunken posts, log-cabin style, as my wall. I'm on heavy clay, which will expand in the wet and shrink in the dry, so I'm not sure a plain brick wall would take the movement.

A wooden solution would be my cheapest option and most easy to source locally (I live 3 minutes from the hardware and garden centre so wouldn't have to pay delivery) but I'm interested to hear feedback on pros, cons, alternatives to wood etc.

OldGoat

Have you concidered gabions? Stone filled wire cages. Cheap enough, can be made to varying sizes and a great place to grow alpines.

Sonnenblumen

MJD

I would suggest you build a double wall: 4" solid blocks/9" cavity laid flat on the inner leaf and on the outer or facing section finish in natural stone (Sandstoen?) or go for a rendered 4" solid laid vertically. Weep hole swould be important as well as backfill wall with plenty of drainage material to minimise any possible water build up. The stone finish would be nice fronting on to road/pathway and the level can fall gradually toward house. A strip perimeter bed can be used to add plant definition and intermittent overhanging planting.

Alternatively you could build one wall say 1 m high and set back 1.0 - 1.2m from boundary edge. The wall would effectively be retaining the embankment and a sloping perimeter palnting strip circumvents the retaining wall, this planting strip can be ramped to accomodate falls and a kerb installed to trap any potential run off water/soil. The retaining wall could also be set to define the prevailing level for lawn but with only 50-75 mm slight raised edge would effectively define the lawn profile. The raised edge can be concealed by tight planting the sloping area with ground cover which can be trained to travel down slope.

I wouldn't be happy with the longterm viability of using wood in this instance to retain the embankment or raised lawn areas securely. I can post you pics if you're interested.

The Sweeper

I would definitely be interested in pics of suggestions.

It's worth pointing out that because of my location, my annual rainfall is considerably less than it would be in Ireland, so treated wood will last 20 years here instead of less than five years in Ireland. My low rainfall means I actually am interested in using the wall and shape on the front garden to catch water when it rains, not necessarily let it run off. I don't have to worry about it becoming a quagmire - let's put it that way. Even in the rainy season, the worst case scenario is that my front garden remains damp for a week, as opposed to wallowing in puddles of standing water that take months to clear.

Sonnenblumen, cavity blocks are very difficult to get here. They're a popular construction material in Ireland, but here most houses are built timber or steel frame with standard housebricks used to build external walls. House bricks I should be able to get - I already have my eye on about a pallet-load of grey coloured brick that's leftover from old construction at my place of work. I can also get those garden type sandstone blocks - the ones with five blank faces and one patterned front, but they're pricey - saying that, I do have to spend some money to do this, so I won't write them off!

I've taken some pics to make what I'm describing seem more clear. I don't know if you guys would even recommend a retaining wall at all - perhaps some overhanging planting would be enough (though I think it would look rough as guts maybe!)

Excuse the chaos in the pics - I've moved most of my "nursery" of plants and they're all stacked up outside for now as I prepare for planting. Actually, they need a bloody good water now that I've just been out looking at them.

Sonnenblumen

MJD,

before posting pics of retaining walls, would you not consider an alternative solution (and a more cost effective one at that). Re-grade the ground to creat a more gentle incline from Driveway to centre area and similarly from along pathway towards centre.

If the prevailing conditions are generally dry, you little to fear in terms of run-off or stability. Walls are a last resort but done well can truely enhance a site. In your case I would also seriuosly consider grading the ground back towards the centre (< 10/15 degree incline) and the acculumated soil can be used to create small elevations/hills which can be planted with low level stock to create heights < 4' or 5' and also creat more uniform levels in central area.

The perimeter areas can be broadly levelled to within 3' and thereafter begin the gentle grading inclines towars centre.

Using walls (and I dont think you require anything like double leaf construction) but would only be a compromise between ground retention and varying site levels. I'd be more inclined (got the pun in !:D) towards developing a soft landscaping solution to your site.

The Sweeper

You mean, sort of like creating gently stepped terraces without the use of hard edges like wood or stone?

Sonnenblumen

No but create a gentle gradient which would involve any step or terracing. In this instance if you create generous but gentle gradients this should make the soil stable. But I would have no worries regarding stability etc.

You might have excess soil in which case this could be redistributed towards the raer of the site, one of your photos showed some quite uneven levels heading towards a white fence. But here grade back from level at fence towards centre and achieve a more uniform level in the central areas.

You could also omit any raised planted beds in the centre. But again these could be planted with a combination of specimen and low level shrubs to create interesting and distinctive islands, eg Mediterranean (Olive, Lavenders), Japanese (Maple, Pieris, Azaleas) , Italian (Cypress,Santolina), Natural Grasses (Stipa, Carex, Acorus) etc etc Some plants will require particular soil conditions (Ericaceous, free draining etc), but this can be easily facilitated.