Building Raised Beds that Last

In the UK and in many parts of the world raised beds have become almost synonymous with the renewed popular interest in vegetable gardening. Gardening catalogs are full of raised bed kits which they claim will get you ‘set up in minutes’ and enjoying your own fresh vegetables without all the hassle of digging or weeding. Not all of these promises are true – raised beds still require hard work in my experience – but there are good reasons why they might work well in your garden. Having gardened using raised beds and a standard flat plot, here’s my guide to deciding if they’re the best option for you and building successful, long-lasting raised beds...

Are Raised Beds Right for Your Garden?

Raised beds don’t suit every garden type. It’s important to weigh up the pros and cons of this gardening method before committing money and time to such a large DIY project:

Benefits of Raised Beds

• Improved Drainage: Because the soil in a raised vegetable bed is higher than the surrounding area water will naturally drain out from it. This is very useful in situations where drainage is a problem – particularly on clay soils and waterlogged vegetable plots.
• Family Friendly: Not treading on soil can help keep the soil structure good for seedlings and reduce or eliminate the need for digging. Keeping children and pets from damaging your prize plants can be a challenge but raised beds clearly separate the growing area from the paths in a way that’s clear even to toddlers.
• Improved Soil: Once a raised bed has been created, you can easily fill it with whatever rich soil and compost you have available. This is much easier than having to dig it into existing ground and often gardeners will fill it with sterile compost giving the vegetables a head-start over the weed seeds that will inevitably come.
• Intensive Planting: With raised beds that are 30cm (12 inches) or higher the extra root depth can provide nutrients for more vegetables allowing you to space them closer. This makes it harder for weeds to establish themselves, significantly reducing the amount of weeding that needs to be done. This is one of the main principles of the Square Foot Gardening method which has become very popular among backyard gardeners.

Disadvantages of Raised Beds

• More Expensive: There’s no getting around it, raised beds cost more than traditional vegetable plots. If you use wood then they will eventually need replacing so it’s important to work out the cost and how many years’ use you will get from them.
• Requiring Irrigation: Because of the increased drainage raised beds often need much more water during warm weather which can require extra work or expensive irrigation systems. This is why the Square Foot Gardening method advocates mixing in vermiculite which helps retain moisture, although I prefer not to use it as it’s not a renewable resource.

Long-lasting Vegetable Beds

Having decided to use raised beds the next question to consider is what material to build them from. The options are:

• Wood: Attractive and easy to install, wood has only one disadvantage – it rots. Some woods last better than others (e.g. cedar) but may cost more and come from unsustainable sources. Various treatments to preserve wood are available but many contain substances that can be dangerous near edible plants. For further details see my article on Treating Wood for Vegetable Gardens.
• Concrete / Brick / Stone: This is the long lasting option but there’s one snag – in my experience slugs and snails love to overwinter in the little crevices within all hard building materials. I have friends who tried to overcome this by using rough roofing tiles in the hope that slugs wouldn’t like crawling up them but no, it takes more than that to defeat a slug!
• Plastic / Composites: There’s an increasing range of plastic options available. Some of the better ones are made by Link-a-bord who use recycled UPVC so it’s as tough as coated window frames and lasts a long time. With an air gap in the middle they claim it also helps insulate plants from frost. However, they are expensive.

My raised beds are in our front garden, so I chose wood as it looks nice and was easy to produce non-standard bed shapes. I decided to not treat the wood but as I didn’t want to be replacing it every few years I used thicker sections than is normally sold for raised beds – 2" x 6" timber doesn’t cost a lot more as it’s a standard building size but it lasts much longer.

Constructing the Raised Beds

For standard rectangular beds it’s quite possible to butt the ends together and quickly construct a box shape that can then be positioned onto the ground. Where the ground is not so even or for irregular shaped beds I found it better to drive a square wooden stake into the ground at each corner (use a wooden mallet) and then attach the raised bed sides to that. Stakes can be bought or made from 2" x 2" wood.

Rather than driving nails into the wood, which can easily split it, a better option is to purchase decking screws which will be galvanized to prevent rust. First a pilot hole slightly thinner than the screw shank is drilled into the timber sides of the bed. Then an electric screwdriver can be used to drive each screw into the post, clamping the two together if necessary to prevent a gap forming and to get a tight fit.

If persistent perennial weeds are a problem then a layer of weed-suppressant fabric can be laid at the bottom. There needs to be good drainage and the wooden sides need to ‘breathe’ so sheet plastic isn’t advisable.

Once the beds are completed it’s time to fill them with good quality compost or soil. For large areas the best option is often to buy recycled compost by the tonne as it is surprising just how much soil is required. Look for good quality potting soil or topsoil that will add plenty of nutrients and retain moisture. This can be topped up every few years to add new nutrients and raise the level where the soil has settled down.

It’s almost two years since I spent a long weekend adding raised beds to my front garden and I’m pleased to say that the thicker wood appears to have paid off – they are holding out very well and I expect to get another 5 – 10 years use from them. After two seasons of crops I would definitely say my raised beds have been a success. For a larger garden or allotment I might look at other options but for enriching soil and helping children access the garden without damaging it they are perfect.

If you have any tips on how to build good raised beds please add them below...