How to build a raised bed

Inspired by a popular UK gardening guide. This walk-through draws on the well-watched "How to build a Raised Garden bed with Diarmuid Gavin" from Wickes, which breaks the whole build into clear, manageable steps. Good for showing how a frame goes together before you start cutting timber in the garden.

1. Choose the right site

Vegetables need sun. Aim for a spot that gets at least six hours of direct light a day — south or south-west facing is ideal. Avoid low spots where water sits, and think about access: you will be visiting this bed daily once things are growing.

Keep the width to around 1.2 metres so you can reach the middle from both sides without stepping on the soil. Length can be whatever suits the space, but two metres is a manageable start for a first build.

2. Choose your timber

Untreated softwood is the budget option and lasts three to five years. Hardwood — oak, chestnut, or Douglas fir — lasts considerably longer. Railway sleepers look great and are very sturdy, though they add weight. Avoid old sleepers that have been treated with creosote around food crops.

Aim for boards at least 150 mm wide and 38 mm thick. You can stack two boards for more depth, which gives roots more room and means the bed retains moisture better in dry spells.

3. Cut and treat the timber

Mark your cuts carefully and use a good handsaw or circular saw. Square cuts make the corners fit neatly. If you are using untreated softwood, paint all cut ends with a water-based preservative before assembly — those end-grain sections absorb moisture and are the first thing to rot.

You do not need to treat hardwood, but a light coat of linseed oil will keep the grain looking good through the seasons.

4. Assemble the frame on flat ground

Use 50 mm square timber posts at each corner as internal corner joints, or buy pre-cut corner brackets. Screw the boards to the posts with 75 mm exterior-grade screws — at least three per joint. Pre-drill to avoid the wood splitting.

Check the frame is square before the screws go fully home. Measure corner to corner diagonally: the two measurements should match. A frame that is slightly off square will show up once it is in the ground and the gaps get wider over time.

5. Prepare the ground underneath

Lay the frame on its intended spot and mark the outline. Remove turf inside the area — cutting it out in slabs makes this easier. Loosen the soil beneath with a fork to improve drainage, particularly in clay-heavy ground like much of Kent.

Line the base with cardboard or a sheet of weed-suppressing membrane if weeds are likely to push through from below. The cardboard rots down over a season and adds to the soil structure. Either way, do not use solid plastic sheeting — drainage needs somewhere to go.

6. Position the frame and fix it in place

Set the frame into position and check it sits level. A slight slope is fine; anything more than 10 mm over the length will cause water to pool at one end. Use a long spirit level.

For a permanent bed, knock 600 mm timber stakes into the ground at each corner and screw them to the frame from the inside. This stops the boards bowing outward once the bed is filled with soil. It matters more than it sounds.

7. Fill with the right compost mix

A good filling mix for raised beds is roughly 60 per cent topsoil, 30 per cent garden compost or well-rotted manure, and 10 per cent sharp grit or horticultural sand for drainage. Avoid using pure compost — it compacts down and dries out badly in summer.

Fill to about 25 mm below the top of the boards so that watering does not wash soil over the edges. The mix will settle over the first few weeks; top it up once it does.

8. Plan what to grow

Raised beds suit salad crops, herbs, root vegetables, and strawberries particularly well. Avoid very tall brassicas in a single-storey bed — they shade everything around them. Think about what you actually cook with and start there.

Rotate your crops each year: do not grow the same family in the same spot twice running. It keeps soil pests and disease under control without chemicals. A simple sketch on paper at the start of each season is enough.

When to call a handyman

Call Richard if the build needs to fit awkwardly around existing paving, steps, or structures, or if you want multiple beds built and levelled properly across a sloping garden. The carpentry side of raised beds is manageable — it is the groundwork on uneven ground that catches people out.