Building a wooden planter box yourself costs between €20 and €80 in materials. Ready-made planters of comparable quality are sold for €50 to €200. Building your own saves you roughly half the cost — and you get to choose the exact dimensions to suit your patio, balcony or garden wall. A planter box is one of the easiest woodworking projects for beginners: you need very little equipment and can be done in 1–2 hours. In this article you’ll find a complete step-by-step guide for a custom-made wooden planter.
Build vs. Buy
| Build yourself | Buy | |
|---|---|---|
| **Small planter (60 cm)** | €20 – €40 | €40 – €100 |
| **Large planter (120 cm)** | €40 – €80 | €80 – €200 |
| **Custom size** | €20 – €80 | Virtually unavailable |
| **Saving** | 40–60% | — |
Materials (planter box 60 × 30 × 30 cm)
| Material | Size | Quantity | Price |
|---|---|---|---|
| Douglas fir boards 18 × 140 mm | 60 cm / 30 cm | 10 pieces | €15 – €30 |
| Timber posts 45 × 45 mm (feet) | 25 cm | 4 pieces | €5 – €10 |
| Stainless steel screws 4 × 40 mm | 30 pieces | €5 – €10 | |
| Pond liner (optional) | 80 × 80 cm | 1 piece | €5 – €10 |
| Wood stain or oil (exterior) | 1 tin | €10 – €20 | |
| **Total** | **€40 – €80** |
Tools
- Circular saw or hand saw
- Cordless drill/driver
- Spirit level
- Sandpaper grits 80 and 120
Step-by-Step Guide: Build a Planter Box in 6 Steps
Step 1: Choose the dimensions and timber species
Standard sizes:
- Small patio: 40–60 cm long, 25–30 cm wide, 25–35 cm tall
- Large patio or garden: 80–120 cm long, 30–40 cm wide, 35–50 cm tall
Timber species for outdoor use:
- Douglas fir — best value for money, naturally weather-resistant, lifespan 15–20 years
- Larch — slightly more expensive, attractive colour, durable
- Pressure-treated pine — cheapest option, requires regular treatment
- Oak — premium, 25+ years, more expensive
Never use chipboard or MDF outdoors — they swell and fall apart when exposed to moisture.
Step 2: Cut all parts to size
Cut the following pieces:
For a planter 60 × 30 × 30 cm:
- 2 × long boards: 60 cm (front and back)
- 2 × short boards: 30 cm (sides) — minus 2 × board thickness (here 18 mm → 30 − (2 × 18) = 264 mm → cut to 26.4 cm)
- Base: boards cut to 26 cm long (fill the 60 cm width with boards leaving 5 mm gaps between them)
- 4 × feet: 5–8 cm high (raises the box off the ground)
Tip: Ask the DIY store to cut the boards to size. It’s more accurate and saves work at home.
Step 3: Sand all parts
Sand all boards with grit 80, then 120. Lightly round over the top edges of all boards with sandpaper — sharp edges splinter quickly.
Step 4: Assemble the box
Lay the four outer walls together. Screw the short side boards to the inside of the long front and back boards (or vice versa — it’s a matter of preference). Use at least 2 screws per joint, always pre-drilling.
Then screw the base boards onto the feet. Leave 5–10 mm gaps between the base boards — this is your drainage.
Finally, screw the walls onto the base-and-feet assembly.
Step 5: Drainage
Option 1: Gaps in the base — leave 5–10 mm gaps between the base boards (the standard recommended approach)
Option 2: Drill drainage holes — drill 3–5 holes of 10–12 mm diameter in the base if you prefer to lay the boards flush
Pond liner: Want to prevent soil sitting directly on the timber? Line the inside of the box with pond liner (leave the base open or perforate it). This significantly extends the lifespan.
Step 6: Treat and finish
Always apply a wood-protective treatment for outdoor use:
- Douglas fir and larch: oil or transparent stain (every 2 years)
- Pressure-treated pine: additional staining or oiling (annually)
Allow the treatment to dry for at least 24 hours before planting.
Variations and Ideas
Planter box on wheels
Attach swivel castors (with brakes) to the underside of the feet. Ideal for a balcony or patio — you can easily move the box for maintenance.
Raised vegetable bed
Build a larger box (120 × 60 × 80 cm) as a raised vegetable bed. Use this working height to avoid back strain. Fill from bottom to top: rough timber/branches (for decomposition), compost, garden soil.
Planter as a divider
Build two tall planters (120 × 30 × 80 cm) and use them as a patio divider. Plant tall grasses, bamboo or hedge plants in them for privacy.
Planter with a slatted pattern
Instead of horizontal boards: stand the boards vertically for a more contemporary look. Or use an overlapping slatted pattern with narrow battens (20 × 80 mm) for a decorative finish.
Common Mistakes
- No drainage. Standing water rots the timber and makes plants ill. Always leave gaps in the base or drill holes.
- Not treating the timber. Untreated timber outdoors lasts 3–5 years. With treatment: 15–20 years.
- Boards too thin. Use a minimum of 18 mm thickness. Thinner boards bow under the weight of soil.
- No pre-drilling. Without pilot holes the timber splits at the screws. Always pre-drill, especially with harder timber species.
Frequently Asked Questions
Which timber is best for an outdoor planter box?
Douglas fir or larch are the best choices for price and quality. They are naturally weather-resistant and last 15–20 years with minimal maintenance. Oak is more durable but also more expensive.
How big should a planter box be?
For flowers and small plants: 25–30 cm tall and 25–30 cm wide is sufficient. For vegetables (tomatoes, peppers) or shrubs: at least 40–50 cm tall and 40 cm wide for adequate root space.
Should I line a planter box on the inside?
Not essential, but pond liner extends the lifespan of the box. Line only the sides and base, leaving the drainage openings clear.
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