How to build a raised garden bed
1st Jan 2015 Home & Garden
This traditional technique could provide you with a bumper veggie crop. Here's how to get the best from raised beds.
Why try a raised bed?
Raised bed gardening is an advantageous way of growing plants and, in particular, vegetables. The general idea is that plants grown in a deep container that sits on the earth will be insulated from the chill of the ground, retaining warmth for longer, thus creating favourable growing conditions for your veggies.
It’s a technique born from traditional permaculture methods designed to maximise cropping; plants are also sown closer together in raised bed gardening, helping create a tight canopy to inhibit weeds, and it also means you are not reliant on the native soil in your garden.
In theory, you could build and fill a bed for plants that thrive in alkaline soil and construct a separate bed for those that prefer to nestle down in soil more acidic.
For those less inclined to DIY, raised beds can be bought in kit form, with a minimal amount of construction required before you are up, running and ready to plant. For those that like to get stuck into a rewarding garden project, there are three main construction types to consider…
Wooden raised beds
Advantages: Easy to build. Cheap(ish)
Disadvantages: Slugs like to hang out in damp, woody recesses. Wood rots so you might need to replace the panels after a few years service.
How to build:
- Choose your wood carefully. Pressure treated wood, although made to prevent premature rotting, has its concerns. Back in the old days, chemicals used in the pressure treating process contain chromated copper arsenate (CCA) which uses arsenic—not the kind of chemical you want leaking all over your spuds. Fortunately, most modern PPT treatment uses Tanalith E, an organic based preservative which is safe to use and will retail your organic vegetable status, if that is an important factor in your gardening. Old Scaffolding boards are a good choice, and another cheap option would be getting hold of a few pallets to break down. Garden centres are a good source of palettes—ask nicely and they might let you have a couple to take home. Steer clear of any blue ones though, these are hire pallets and unless you want a fine landing on your doorstep. They shouldn't be touched, let alone set upon with a hammer and saw.
- Use square retaining stakes for each corner, and for maximum stability, every metre. Hammer the stakes into the ground to a depth of 50 cm.
- Fix your wooden panels to the retaining stakes. Screws will last longer and make things easier if you want to deconstruct your work, but nails are the quickest option. Whatever you choose, make sure they are galvanised for maximum corrosion protection.
- Don’t forget the spirit level! Keep checking your levels as you go.
Brick walled raised beds
Advantages: Built to last, bricks won’t rot
Disadvantages: Time consuming and costly to make. You’ll need a bit of basic brick working skill to construct a brick bed
How to build:
- Mark out the designated area using stakes and string.
- For a strong and secure bed wall, put down a hardcore base approx 10 cm deep before laying your bricks.
- If you plan to construct your brick raised bed on concrete or an existing patio, leave the odd gap between brick joints to provide drainage. Cover the holes with mesh to stop them clogging.
Sleeper raised bed
Image via Railway Sleepers
Advantages: Looks the biz. Will last for years
Disadvantages: Sleepers can be expensive to purchase and can potentially leak undesirable chemicals into your soil
How to build:
- Choose your sleepers carefully—old railway sleepers may look lovely and rustic, but will most likely have been treated with tar and creosote which will seep into your soil in warm weather. Look out for new, softwood sleepers that have been treated with eco-friendly preservatives. You’ll also find that these types are also a lot lighter, making them easier to move around the garden.
- Ensure the ground you intend to build on is firm and level.
- Overlap the sleepers like brickwork if you are building a bed more than two sleeper levels high.
- Fix in position by hammering metal rods into the ground, either side of the sleeper walls.
Filling your raised bed
To aid drainage, first lay an 8 cm layer of gravel or stones, on top of which lay a weed inhibiting membrane. Fill your bed with topsoil. If you can, avoid filling with soil sourced from elsewhere in the garden to prevent any weed contamination.
Remember to add a generous amount of well rotten manure, and dig over the area thoroughly before planting.
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Nick and Rich run the website twothirstygardeners.co.uk and their home-grown booze recipe book, Brew it Yourself, is out now
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