At a glance
Garden bed edging does more practical work than most gardeners give it credit for. A well-installed border between lawn and planting bed prevents grass from creeping into the border, holds mulch and bark chip in place rather than letting it wash onto the lawn, and provides a clean mowing line that saves fifteen minutes of hand-trimming after every cut. The visual effect is equally significant: the same border looks twice as good when the edge is defined cleanly, regardless of what is growing in it.
The range of edging materials available to UK gardeners has expanded considerably in the past decade. Pressure-treated timber boards, steel and aluminium profiles, recycled plastic, natural stone sets, brick and terracotta are all options, each with different installation requirements, longevity expectations and aesthetic outcomes. Choosing the right material for the situation and then installing it so it stays true over successive seasons of ground movement, frost and wet weather is what separates an edge that looks good for years from one that is listing and gappy by the following spring.
What you’ll need
Choosing your edging material
Material choice should be driven by three factors in this order: how long you need it to last, whether the bed edge is straight or curved, and what aesthetic best suits the garden. A formal parterre with crisp straight lines calls for a different solution to a naturalistic curved border planted for wildlife. Getting the material wrong for the situation – fitting rigid timber to a serpentine bed, or choosing flexible plastic for a formal kitchen garden with 90-degree corners – creates unnecessary difficulty at the installation stage and an unsatisfying result.
Pressure-treated timber remains the most practical choice for the majority of UK raised bed installations. It is inexpensive, widely available in standard lengths and sections, easy to cut and fix on site, and when correctly specified at UC3 or UC4 treatment class will last ten to twenty years without maintenance. Corten steel has grown significantly in popularity and the combination of outstanding longevity, excellent flex for curves and the distinctive weathered rust patina makes it the premium option for anyone who wants a permanent, low-maintenance installation. Aluminium profiles hit a useful middle ground – genuinely flexible, lightweight, corrosion-proof and available in widths and depths to suit most applications.
Marking out and setting a true line
The single step that determines whether edging looks professionally installed or merely functional is the quality of the line set before any edging goes in the ground. A true, even line – whether straight or curved – allows every subsequent step to work cleanly. An inconsistent reference line produces wobbles that are visible from twenty metres away once the edging is in and impossible to correct without lifting the whole run and starting again.
For straight runs along a lawn or path edge, drive two canes at each end of the proposed edging run and pull a string line taut between them at the desired edging height. Run a half-moon edging iron or spade along the string line to create the initial slot, pulling the soil back slightly to create a clean vertical face. The slot depth should equal the full depth of the edging material plus 10-15mm for bedding the base firmly. Cutting the slot cleanly at this stage is the difference between edging that sits solid and level and edging that rocks when pressed.
The slot must be slightly deeper than the edging, not shallower. A common mistake is slotting to exactly the depth of the edging material, which means the edging cannot be driven to its final position without lifting and respacing soil from below. Slot to the edging depth plus 15mm, then backfill and firm up once the edging is positioned. This gives controlled final positioning without needing to recut.
Installing by edging type
Each edging material has a specific installation sequence. The marking-out and slotting preparation is identical regardless of material, but the fixing method, jointing approach and height setting differs meaningfully between timber, metal strip and flexible plastic. Following the correct sequence for the material being installed produces a result that stays in place through frost heave and wet winters rather than one that begins working loose by the first autumn.
Timber boards – drive stakes first, boards second
Cut 50x50mm pegs to 300mm length and sharpen one end with a saw. Drive pegs into the slot at 600-800mm intervals using a rubber mallet, keeping the inner face flush with the string line. Once all pegs are in place, hold the board against the pegs and fix with two screws per peg using an impact driver. The board should sit with its top edge at or just above lawn level – checking this with a long spirit level before fixing any screws.
Metal strip (corten or aluminium) – stake and peg connectors
Metal edging strips arrive in 1-2 metre lengths and connect via manufacturer-specific joining pegs or simple overlapping. Start at one end of the run and drive the first stake into the ground to set the height. Feed the strip along the slot, securing with stakes at the intervals specified by the manufacturer – typically 400-600mm. At joins between strips, overlap by at least 50mm and drive a fixing stake through both layers. Pull the strip taut as you go rather than letting it bow between stakes.
Flexible plastic – peg into place and tension as you go
Modern recycled plastic edging has significantly more rigidity than older black polythene products and installs much like metal strip. The key difference is that plastic expands slightly in summer heat – install with a very slight bow between stakes rather than pulling absolutely taut, to allow for thermal movement. Cutting ends cleanly with a multi-tool produces neater joins than a hacksaw, which tends to produce a rough ragged cut.
Brick or stone – bed on mortar for permanence
Brick edging set on a full mortar bed produces the most permanent result but is significantly more labour-intensive than strip edging. Dig the slot wide enough to accommodate a brick laid on its side plus a mortar bed. Mix a stiff 4:1 sand-cement mortar and lay a consistent bed. Set each brick to the string line, checking with a level every three bricks. Point the joints with a stiff mortar mix and wipe clean before it sets. Allow 48 hours before exposing to rain.
Cutting curves and corners
Curves are where most edging projects either look considered or look amateur. A smooth curve that sweeps cleanly around a bed is achieved before any cutting – it is the shape of the ground reference line that determines the outcome, and that line is set with the hose method described in the marking section. Once the curve is marked and the slot cut to follow it, flexible metal and plastic strips follow naturally. Timber boards cannot follow a curve and should never be forced to – the correct solution for a curved bed with timber edging is to cut a series of short boards and angle the joints between them, creating an approximation of the curve from straight segments. Cutting each board on a slight angle at each end with a mitre saw produces a neater join than square-cut boards butted against each other.
Finishing, maintenance and common mistakes
Once edging is installed and backfilled, the final step is to firm the soil on both sides of the edging run using the back of a rake or the sole of a boot. Loose soil on the border side allows the edging to lean inward as the season progresses. Loose soil on the lawn side creates a soft line that means the mower sinks slightly when tracking along the edge, defeating the purpose of having a defined mowing line. Both sides should be firmly consolidated immediately after installation, before the first watering or rainfall disturbs them.
Never set timber edging boards directly on soil without pegs. Boards laid flat without proper stake fixing will shift with every frost and every heavy rainfall. The pegs are the structural component – the board is simply the visible face. A board without adequate peg support will have tilted, lifted or sunken by the following spring and cannot be relevelled without lifting the whole run. Always drive at least one peg per 600mm of board length.
The most common long-term failure in garden bed edging is not the edging itself but the soil level management on each side. Edging is set at a specific height relative to both the lawn and the bed, and that relationship must be maintained over time. Topping up the bed with compost each year gradually raises the soil level inside the edging until it overflows onto the lawn; not topping up creates a trench effect where the bed sinks below the edging height. Check the relative levels when adding compost to beds each autumn and adjust accordingly. A raised bed with well-maintained edging alongside carefully chosen plants – whether low-growing herbs, structural box hedging or flowering perennials – reads as a coherent, deliberate space rather than an arbitrary boundary between one surface type and another.
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