Raised Timber Planter
A simple garden planter for patios, borders and vegetable growing, with guidance on timber durability, lining, drainage and safe material choices.
What you'll need
Materials
- Boards or sleepers for sides
- Corner posts or internal cleats
- Breathable liner or membrane
- Drainage gravel
- Galvanised or stainless screws
Tools
- Tape measure
- Combination square
- Saw (circular or hand)
- Drill/driver with bits
- Clamps (optional)
Material complexity: Low
Buy one spare 2.4m board. Caps and shorts come out of it with less waste.
Main risk: Wrong use class for soil contact, or no drainage — the timber stays wet and the plants sit in a sump.
Cut list
Default 1.2 × 0.6 × 0.45m bed, single-skin 150×25mm boards, three courses, posts inside the corners. Confirm on site.
- Long boards ×6150×25mm × 1200mm
- Short boards ×6150×25mm × 550mm (butted between the longs — 600 minus two 25mm faces)
- Corner posts ×447×47mm × 450mm, inside each corner
- Cap boards ×2145×22mm × 1280mm
- Cap boards ×2145×22mm × 680mm
- Breathable liner or membrane for the inside faces
- About 50mm of drainage gravel in the base
- Galvanised or stainless screws, typically 4.5–5.0×50mm board-to-post. Pre-drill oak and larch
Fill: about 280–320 litres of compost and soil after the gravel (roughly six 50-litre bags).
Sleeper variant: four 200×47mm × 1200mm longs and four 200×47mm × 506mm shorts, two courses. Double-skin the 150×25mm boards if you want a stiffer box — double the board count.
Step-by-step
Mark out and cut the box parts
Decide internal size (a 1.2×0.6m footprint at 450mm high is a comfortable default). Cut long sides, short sides and corner posts or cleats to length. If you are doubling boards for stiffness, cut pairs together so lengths match.
Tip: Pre-drill end grain on oak and larch — screws in end grain alone will not hold for long outdoors.
Assemble the frame
Screw the box together with posts behind corners or cleats inside. Keep the top edge flush and check diagonals are equal before the last screws go in. Clamp if you can — a twisted box is hard to fix once loaded with soil.
Watch out: Use UC4-rated stock for any timber in direct soil contact, or keep the box on feet with airflow underneath.
Add drainage and liner
Drill several 10–12mm holes through the base, or leave a gap between boards. Lay membrane or heavy-duty liner so soil does not sit against timber, but do not trap water in corners — fold and staple neatly, then pierce the liner over drainage holes.
Tip: A 50mm gravel layer under the soil helps drainage on patios and reduces splash-back onto the boards.
Cap the top edge
Fit a wider cap board or mitred trim over the top edge to shed water and protect end grain. Slope the cap slightly outward if you can. This is the detail that keeps the planter looking sharp after the first winter.
Position, fill and maintain
Set the planter level on feet, pavers or a gravel strip — not directly on lawn without a gap. Fill with compost and soil mix. In year one, check corners after frost; refresh soil and re-tighten fixings as the timber settles.
Tips & traps
- No drainage — roots drown and timber stays wet.
- Wrong treatment class for soil contact.
- Liner folded so water pools in corners.
- Top edge left uncapped — end grain soaks and splits.
Planning & timber detail
Why build this?
Raised planters are the ideal first timber project — few joints, immediate usefulness, and a clear lesson in durability classes and drainage.
Where it works best
Level patios and firm soil. Avoid placing directly on lawn without a gap for airflow. Good for veg where native soil is poor.
Planning notes
Include drainage holes through the base or use a gravel layer. Membrane between soil and timber extends life. Consider a capillary break if the box sits on paving.
Typical sizes
Default box: 1200 × 600 × 450mm outside.
Three 150mm boards give 450mm. Sleepers in 200×47mm, two courses, finish about 400mm — close enough, and heavier.
Double-skin the thin boards if you want stiffness without thick stock.
Default dimensions
Default footprint: 1200 × 600mm.
Height: 450mm (three 150mm boards).
Comfortable access: 400–600mm high.
Design variants
Board box (this page) — 150×25mm, three courses, internal corner posts. Light enough to move empty; line it.
Sleeper box — 200×47mm, two courses. Heavier, fewer joints, good on soil.
Double-skin — two layers of 150×25mm. Stiffer than single-skin without thick stock.
On feet — lift the box onto pads or paving so you can use UC3 timber (kept off the soil) instead of UC4 (in soil or stays wet).
Suitable timber options
Treated redwood is the practical default for ground contact. Oak sleepers last decades but are heavy. Cedar works above paving if not in constant contact with wet soil.
Fixing and finishing
Screw from inside so heads are hidden. Use galvanised or stainless. Pre-drill oak and larch. Butt joints at corners with posts behind are stronger than screwing into end grain only. Cap the top edge to shed water.
Cap top edges to shed water and protect end grain. Butt joints at corners with posts behind are stronger than screwing end grain only.
Maintenance
Refresh soil every few years. Check corners for rot where liner traps moisture against timber.
Top up compost annually. Replace liner if it fails before the timber rots.
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 the box sits on feet or paving with air underneath. A liner reduces how often the inside face gets soaked.
Movement
Wide boards cup — screw from inside with allowance, or use narrower boards. Sleepers are heavy but stable.
Go deeper
Related yards
Get the Timber Buying Companion
An 8-page practical guide to choosing better boards, avoiding waste and spotting common timber problems before you buy.