Raised Bed System
Multiple raised beds laid out as a vegetable garden or allotment system — sizing, path widths, durable species and a path-and-bed module that scales from one bed to twenty.
What you'll need
Materials
- Boards or sleepers, corner posts or screw-together corners, stainless screws, weed membrane for path bases, woodchip or gravel for paths, compost mix for beds.
Tools
- Drill/driver, mitre or hand saw, spirit level, tape measure, spade for ground prep, optional weed membrane stapler.
Material complexity: Low
Buy boards in 2.4m lengths — they suit 1200/2400 beds with almost no offcut. One spare board per three beds is enough.
Main risk: Building one bed with no plan for paths — the system turns into a maze you cannot work or water.
Cut list
One 1200×2400×450mm bed in 150×47mm boards, three courses. Repeat the list for each extra bed.
- Long boards ×6150×47mm × 2400mm
- Short boards ×6150×47mm × 1106mm (1200 minus two 47mm posts)
- Corner posts ×447×47mm × 450mm, inside each corner
- Optional mid posts on the longs ×247×47mm × 450mm — useful if the 2.4m sides start to bow
- Liner or membrane for the inside faces (and a separate weed membrane for the paths)
- Galvanised or stainless screws, typically 5.0×70–80mm, from the inside into the posts
Compost: the empty box is about 1.3m³. After 50mm of gravel, plan on 1.15–1.3 cubic metres of compost and soil — roughly 23–26 bags of 50 litres, or one bulk cubic metre plus a few bags.
Sleeper variant: 200×100mm, two courses (400mm high). Four 2400mm longs and four 1200mm shorts come from six 2.4m sleepers if you cut two in half for the ends.
Step-by-step
Mark beds and paths before you buy a board
Peg out every 1200×2400mm bed and the paths between them. 600mm is the minimum path; 900mm if a wheelbarrow has to pass. Walk the routes. If you cannot kneel beside a bed, the path is too tight.
Tip: Orient beds north-south so one row does not shade the next.
Cut one size, in one batch
Cut all 2400mm longs and 1106mm shorts for the first bed in one go. Three courses of 150×47mm give 450mm. Keep the offcuts labelled — the next bed uses the same list.
Tip: 2.4m merchant stock suits this size. Do not start from random leftovers or the system stops being modular.
Assemble the box on level ground
Stand 47×47mm posts in the four corners. Screw the boards from the inside, two screws per board into each post. Check diagonals before the last screws. Add a mid post on a 2.4m side if it bows when you lean on it.
Watch out: If the timber will sit in soil it needs UC4 (timber that sits in soil or stays wet). UC3 is only for boards kept off the soil by membrane and gravel.
Line, gravel, then fill about 1.2m³
Line the inside so soil is not hard against the boards, but pierce the base so it can drain. A 50mm gravel layer helps. Then fill with a compost and soil mix — plan on 1.15–1.3 cubic metres per bed (about 23–26 × 50-litre bags, or one bulk bag plus a few extra).
Tip: Do not cheap out on the fill. A perfect box of poor soil grows a poor crop.
Build the paths as part of the job
Lay weed membrane on the marked paths and cover with woodchip or gravel. A bed without a path is half finished. Top up compost each spring as it settles; swap a single failed board rather than rebuilding the system.
Tips & traps
- Paths too narrow — a 400mm gap looks fine on paper and is useless with a barrow or a kneeling pad.
- Every bed a different size — you cannot reuse boards or plan compost.
- No corner posts, so 2.4m sides bow once they are full.
- Filling with garden soil only — use a compost mix, and budget the volume before you build.
Planning & timber detail
Why build this?
A modular raised-bed system turns a patch of lawn into a kitchen garden you can actually work. Built on a planned grid with proper path widths, it scales from two beds to twenty and stays organised instead of becoming a cluster of odd boxes.
Where it works best
Level or terraced ground with reasonable sun (6+ hours daily for veg). Allow space for paths and for sitting and working around the beds — most first gardens are over-bedded and under-pathed.
Planning notes
Plan the whole system before building one bed — layout, path widths, water, compost bin. Isolated beds tend to grow into a mess. Orient beds north-south so plants do not shade each other.
Typical sizes
Default one bed: 1200mm wide × 2400mm long × 450mm high.
1200mm is as far as most people can reach from one side without stepping in. 450mm is comfortable kneeling; 750mm is comfortable standing.
Paths: 600mm minimum, 900mm if a wheelbarrow has to go through.
Default dimensions
One bed: 1200 × 2400 × 450mm.
Paths: 600mm minimum, 900mm for a wheelbarrow.
Reach: 1200mm from one side; 600mm wide if you only access from both sides.
Design variants
Board bed (this page) — 150×47mm, three courses. Light, cheap to repeat.
Sleeper bed — 200×100mm, two courses. Heavier, fewer joints, the showpiece option in oak.
Standing height — 750mm, five 150mm courses. Kinder on knees; more compost.
The system — standardise one bed and one path width, then repeat. Do not invent a new size for bed three.
Suitable timber options
Treated redwood is the scale-friendly default — multiple beds get expensive in oak. Larch is a halfway point that lasts longer than treated redwood. Use oak sleepers for one or two showpiece beds if budget allows.
Fixing and finishing
Screw from inside so heads are hidden. Galvanised or stainless, typically 5.0×70–80mm into 47×47mm corner posts. Avoid copper-based treated timber if growing food directly against the wood — modern treatments are generally considered acceptable, but read the product.
For a modular system: standardise on one bed size and one path width. Cut all boards to length in one batch. Assemble corners with vertical posts (47×47mm or similar) inside the corner for screw bite and stiffness.
Maintenance
Top up beds annually as compost settles. Replace individual boards as needed — system design lets you swap one without rebuilding everything.
Lift and replace any board that fails individually. The system is its own spare-parts kit.
Timber behaviour
Durability
UC4 for timber in soil — UC4 means timber that sits in soil or stays wet. UC3 (timber kept off the soil) is enough if you isolate the boards with membrane and a gravel strip. Treated redwood is the practical default at this scale. Check the treatment if you are growing food against the wood.
Movement
Long boards on a single bed will bow if not corner-supported. Use intermediate posts every 1.2m on beds longer than 2.4m to prevent bellying as wet soil swells the timber.
Go deeper
Related yards
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