How to Build a Raised Garden Bed – DIY Guide
Build a raised garden bed by cutting timber planks to length, screwing them into a rectangular frame with corner posts, positioning the bed on prepared ground, lining the base with weed-suppressing membrane, and filling with a mix of topsoil and compost. The whole job takes half a day.
- Tape measure
- Pencil
- Hand saw or circular saw
- Cordless drill/driver
- Mallet
- Spirit level
- Staple gun
- Safety goggles
- Pressure-treated timber planks (100mm x 38mm or similar)
- Timber corner posts (75mm x 75mm)
- Exterior wood screws (75mm)
- Weed-suppressing membrane
- Galvanised staples
- Topsoil
- Garden compost or well-rotted manure
- Horticultural grit (optional, for drainage)
Step-by-Step Guide
Mark Out and Prepare the Site
Choose a level, open spot that receives at least six hours of sunlight daily — this is the single most important decision for a productive bed. Use a tape measure and bamboo canes to mark out your bed footprint; a width of 1.2m is ideal so you can reach the centre from either side without stepping in. Remove any turf or weeds within the marked area and roughly level the surface with a spade. For more inspiration on what else you can add to your outdoor space, browse our Garden Guide.
Cut Timber to Length
Measure and mark your planks accurately with a tape measure and pencil before cutting — measure twice, cut once. For a standard 2.4m x 1.2m bed, you will need two planks at 2.4m and two at 1.2m for each course; double up the courses for a 200mm–250mm final height, which gives roots adequate depth for most vegetables. Use a hand saw or circular saw to cut cleanly, and wear safety goggles throughout. Pressure-treated timber is essential — untreated softwood in contact with damp soil will rot within two seasons.
Assemble the Frame
Stand your corner posts upright on a flat surface and butt the end planks flush against the inside face of each post. Drill pilot holes first to prevent the timber splitting, then drive two 75mm exterior screws through the plank and into each post — one near the top of the plank, one near the bottom. Repeat for all four corners, building up each course before adding the next. Check the frame is square by measuring diagonally corner to corner; both measurements must match. A mallet is useful for tapping planks into alignment before you drive the screws home.
Position and Level the Bed
Carry the assembled frame to your prepared site and set it in position. Place a spirit level along each side in turn; if the bed rocks or sits out of level, pack underneath with a little soil or remove material until it sits flat. Driving the bottom 50–75mm of each corner post into the ground with a mallet will anchor the bed and stop it shifting over time — this step is especially important on a slope. If your garden has a persistent drainage problem, you may want to read our guide on how to scarify and aerate a lawn to understand soil compaction before filling.
Line the Base and Fill
Cut weed-suppressing membrane to cover the entire base of the bed, overlapping the sides by 50mm, and fix it in place with galvanised staples. This stops persistent weeds pushing up from below without blocking drainage. Fill the bed with a mix of 60% good-quality topsoil and 40% garden compost or well-rotted manure — this ratio gives you fertile, moisture-retentive growing medium that won’t compact hard. If drainage is a concern, work in a handful of horticultural grit per square metre. Firm the mix gently with your hands rather than stamping it down, and top up to within 25mm of the rim to allow for watering. You can fill a raised bed cheaply by using homemade compost and sourcing topsoil locally.
Finish, Treat, and Plant
If your timber was not already pressure-treated, apply an exterior wood preservative to all exposed surfaces and allow it to dry fully before planting. Check the frame is still level and square after filling — the weight of soil can shift things slightly. Water the bed thoroughly before planting to settle the growing medium and reveal any low spots that need topping up. If you plan to add paths around your beds, our guide to how to lay paving slabs covers the groundwork clearly.
Frequently Asked Questions
What is the best timber to use for a raised garden bed?
Pressure-treated softwood is the most practical choice — it resists rot and is widely available in standard sizes. For edible crops, ensure any treatment is certified safe for food-growing use; untreated oak and larch are naturally durable alternatives if you want to avoid preservatives entirely.
How deep should a raised garden bed be?
A minimum of 200mm is needed for most salad crops and herbs; 300mm is better for root vegetables such as carrots and parsnips. Shallower beds work for strawberries and alpine plants but will dry out quickly in summer.
Do I need to line the sides of a raised bed?
Lining the sides is not necessary and can actually trap moisture and accelerate timber decay. Lining only the base with weed-suppressing membrane is sufficient — the sides should be left open to allow water to move freely through the timber.
Can I build a raised bed directly on a patio or decking?
Yes, but drainage becomes critical — ensure water can escape through the base or the roots will waterlog. Place the bed on feet or battens to raise it slightly, and lay gravel in the base beneath the membrane before adding soil. Check the load-bearing capacity of decking before filling, as a large bed of wet soil is considerably heavy. If you are working near decking, our guide to how to lay a patio covers base preparation in detail.
What should I fill a raised bed with?
A 60:40 mix of topsoil and garden compost or well-rotted manure gives the best results for most edible crops. Avoid using soil dug straight from the garden — it compacts badly and often brings weed seeds with it. You can read more in our guide on how to fill a raised bed cheaply.
Screw a diagonal batten across each internal corner at the base of the frame before filling — this stops the sides bowing outward under the pressure of wet soil, which is the most common reason raised beds look shabby after their first winter. A single 400mm batten per corner takes two minutes to fit and adds years to the life of the structure.
Sources
- RHS — Raised beds: how to make and maintain them — rhs.org.uk
- HSE — Safe use of wood preservatives — hse.gov.uk
- Which? — How to build a raised bed — which.co.uk
This guide is for general information only. Always work safely and follow manufacturer instructions. DIYnut accepts no liability for injury or damage arising from DIY work.
