Installation of Palisade Edging Over 50 cm High

Low palisades up to 50 cm are mainly edging. They separate a path from the lawn or form a low raised bed. Once they get taller, their job changes. The soil behind them pushes outwards and gets heavier after rain, and the palisade has to resist that pressure for years without leaning.

Tall palisades suit these situations:

• Levelling the ground around a new house on a slope
• Terracing a garden into several flat areas
• Holding back an embankment next to a driveway or parking space
• Raised beds and separating a seating area from a vegetable or utility area

Compared with a solid concrete wall, they look lighter and more natural. As the height grows, or if cars will drive or park behind the wall, this stops being ordinary garden work. At that point it is worth having the design checked by a structural engineer.

Concrete palisades

For heights over 50 cm these are the usual choice. They are strong, cope well with frost and damp, and need almost no maintenance. They come in various colours and finishes, often imitating stone or timber, so you can match them to block paving or the house.

Reinforced palisades

Taller walls and higher soil pressure call for elements with steel reinforcement. The reinforcement increases load capacity and reduces the risk of an element snapping under pressure. Whether you need them depends on the height and loading. The manufacturer's technical data or a structural engineer will tell you.

Timber palisades

They look natural, but at greater heights and in constant contact with soil they last much less time and need regular treatment. They suit decorative, lightly loaded parts of the garden rather than the main retaining wall.

Appearance is only part of the decision. Soil type, the height of the level change, how much water is around and whether the area behind the wall will be lawn or hard surfacing all matter. If the manufacturer gives a maximum retaining height for a product, stick to it.

To give you an idea of what happens on site, this is the usual sequence a contractor follows:

1. Check for underground services and set out the line with string and pegs.
2. Dig the foundation trench. The depth depends on the palisade height, the soil and the load. Manufacturers often state that roughly a third of the element's length should sit in the foundation.
3. Compact the bottom of the trench and, where needed, add and compact a gravel layer.
4. Lay the concrete bed and set the palisades into the fresh concrete one by one.
5. Check height, line and plumb as work goes on, using a spirit level and string line or a levelling instrument.
6. Haunch the back with concrete as well, so the palisades act as one solid unit.
7. Let the concrete cure as the manufacturer recommends, usually several days, before any backfilling.
8. Lay a drainage pipe, geotextile and gravel backfill behind the wall, compacting it in layers.
9. Tie in the surrounding areas, such as paving, steps or lawn.

If the palisades meet block paving, the final step is spreading sand and brushing it into the joints.

Why do tall palisades sometimes start leaning after a few years? Almost always the cause is water or a weak foundation. Wet soil is heavier and pushes on the wall much harder than dry soil. If the water has nowhere to go, the pressure keeps rising and the ground underneath slowly softens.

That is why the space behind the palisades is not simply filled with the dug-out soil. Gravel or crushed stone is used, because water drains through it, with a perforated drainage pipe at the bottom leading to a place where water can run off safely. Geotextile keeps the gravel separate from the soil so it does not clog over time. The ground above the wall should fall gently away from it, not towards it.

Compacting in layers matters just as much. If the backfill goes in all at once, it settles later, rain soaks the soil behind the wall and the palisades are pushed unevenly.

How demanding the job is, and so how much work it takes, varies a lot from plot to plot. Things are easier on level, accessible ground where a mini digger and a concrete delivery can get in, with firm, stable soil and a short, straight run.

These factors make the job harder:

• A steep slope and a large difference in ground level
• Poor access, so materials have to be carried or barrowed in
• Wet, clay or made-up ground
• Curves, steps and connections to paving or walls
• Services close to the trench and a lot of spoil to remove
• Vehicles loading the ground behind the wall, which needs a sturdier design

Doing this yourself is not recommended at this height. It is a retaining structure, and mistakes only show years later, when the wall starts moving with the soil.

• A shallow trench or too little concrete in the foundation, so the palisades lean
• No drainage, and backfill with soil instead of gravel
• Backfilling before the concrete has cured
• Pouring concrete in frost without protection
• Inaccurate setting, which looks poor and loads the wall unevenly
• Underestimating soil pressure at a height that really needs an engineer
• Using palisades meant for low edging in a tall retaining wall

When you accept the work, walk the full length of the wall and check these points:

• The palisades are plumb and the top edge keeps the agreed height or a smooth fall
• The line is straight, with no elements pushed out or sunk
• There are no wide gaps between palisades that soil could spill through
• The foundation concrete is solid, with no visible voids
• There is gravel backfill and drainage behind the wall with a clear outlet
• The ground above the wall falls away from the palisades
• No elements are cracked or spalled
• Connections to paving, steps and lawn are neat and stable
• The contractor has given you details of the materials used and the manufacturer's recommendations

After that, an occasional check is enough, especially after heavy rain and winter. Look for leaning or cracking, and make sure the drainage is still carrying water away.