Installation of Palisades up to 50 cm High

An edging strip only separates paving from lawn. A palisade can also handle a small difference in level, such as a raised bed, a stepped transition by a patio or the edge of a gentle mound. A height of up to 50 cm suits an ordinary garden: it holds soil, does not look heavy and needs no complex calculations.

Keep in mind that part of every palisade sits in the ground. A 50 cm element shows less above ground, roughly two thirds of its length. If you need to hold back a larger slope, or a car or heavy load will stand behind the palisade, you are really building a retaining wall. A retaining wall should be assessed by a professional and usually needs a deeper concrete foundation.

Low garden palisades usually do not need permission. Rules vary by country and region, though, and depend on the specific work. For retaining walls, changes to ground levels on the boundary with a neighbour, or work around a block of flats, check with your local building authority beforehand whether you need to notify anyone or apply for anything. If you live in a flat, agree the work with the building management or owners' association first.

Concrete palisades are very hard-wearing. They cope with frost, damp and soil pressure, and when properly set they last for many years. You can get them in grey or coloured versions, with surfaces that imitate stone or wood. For slopes, areas close to the house and driveways they are the usual choice.

Timber palisades look natural and go in quickly. Wood in the ground will sooner or later give in to moisture and rot, even when it has been pressure-treated. They suit decorative bed edges better than holding back soil.

Plastic and composite palisades are light, do not rot and need almost no maintenance. They are not as strong, so use them to separate areas visually rather than to retain ground.

A simple rule: the more pressure the palisade will take, the more you should lean towards concrete elements set in a concrete bed.

1. Setting out. A string line and pegs mark the route and the height of the top edge. A garden hose or marker spray helps with curves.
2. Digging. A trench is dug deep enough for the sub-base, the bedding layer and the buried part of the palisade. This usually means at least a third of the element's length plus the base.
3. Sub-base. Gravel or crushed stone goes into the bottom and is compacted thoroughly. This layer carries the load and lets water drain away.
4. Bedding. For light edges a compacted gravel bed is enough. On a slope, under heavier load or in soft ground the palisades are set in concrete, usually a semi-dry, earth-moist mix.
5. Setting. The palisades go in one by one along the string line and are tapped level with a rubber mallet. Plumb, line and height are checked continually with a spirit level or a laser.
6. Back support and drainage. On the side where the soil will be, the palisades are haunched with concrete, and drainage gravel goes behind them. In wet ground a perforated drainage pipe is added.
7. Backfilling and finishing. Finally the trench is backfilled, the soil lightly compacted and the surroundings joined neatly to the lawn, bed or block paving.

Why so much attention to the base? Soil freezes in winter and soaks up water in spring. If the base is not firm and free-draining, the palisades start to lean after the first winter.

The job is quicker and simpler on a straight line across level, firm ground, with easy access for a wheelbarrow and materials. Things that make it harder:

• A slope and the need to retain soil, which calls for a concrete bed and back support
• Curves and changing heights, where each piece has to be adjusted on its own
• Clay or waterlogged soil, which needs a deeper base and drainage
• Tree roots, stones or old concrete footings in the trench
• Poor access to the site and a lot of excavated soil to take away
• Buried services along the route, which must be located before digging

If you hit a gas pipe while digging, or you smell gas, stop work at once, move away from the area and call the gas emergency line or the local emergency number (112). Any repair to the pipe must be done by a qualified, registered gas engineer.

You can handle a low edge on level ground yourself. If the palisade has to hold back a slope, stands next to a driveway or will have heavy machinery passing over it, leave the job to a contractor.

1. Check that no cables or pipes run along the route.
2. Set out the line with string on pegs and mark the height of the top edge.
3. Dig a trench with enough depth for the sub-base, the bedding and burying at least a third of the palisade.
4. Spread gravel and compact it with a hand tamper or a hired plate compactor.
5. Mix semi-dry concrete according to the manufacturer's instructions and spread the bed.
6. Set the first palisade, check it with a spirit level and add the next ones tight against each other.
7. Tap each piece into line with a rubber mallet, following the string.
8. Add concrete haunching at the back and leave it to harden for the time the manufacturer states.
9. Pour drainage gravel behind the palisades, then soil, and compact it lightly.

• Poorly compacted base. The palisades settle unevenly and the line starts to wave.
• Set too shallow. A short buried section cannot resist the soil pressure and the elements tilt outwards.
• No drainage. Water behind the palisade pushes against it, freezes in winter and gradually forces it out.
• Wrong material. Timber or plastic on a slope where concrete belongs.
• No back support. The palisades stand in gravel only, even though they hold soil.
• Line not checked. On a longer run even a small deviation is easy to see.

• The line is straight or curves smoothly as planned
• The top edges are level or follow the agreed fall, with no steps between pieces
• The palisades stand upright and do not move when you push them by hand
• There is concrete haunching and drainage gravel at the back wherever the palisade holds soil
• The gaps between elements are even
• The joins to paving, lawn or beds are neat and without holes
• Water does not stand behind the palisade after rain
• The area is tidied up and surplus soil has been removed