Of all the larger scale garden construction jobs, this is certainly one of the easiest and one of the most rewarding. Building a raised bed for your garden is a beginner level project that can be completed in just a few hours.
The benefits of a raised bed
Less bending over is one of the key benefits. As the years go by, this becomes more and more attractive to every gardener. In addition, raised beds are easier to control, and the soil is so much lighter because nobody walks on a raised bed. The soil doesn’t get compacted, so the worms find it easier to work through the contents, helping the gardener as they go. You can also start growing a little earlier in the season. The extra drainage allows the soil to warm up a bit faster in Spring, giving you at least an additional week or two.
To build a raised bed you will need the following tools from the shed:
- A Spade
- A Spirit Level
- A Saw
- A Drill
- A Screwdriver
- A Paintbrush
- A sander or plane (optional for smoothing the wood)
The rules for building a raised bed
There are actually very few rules when it comes to building raised beds, so there are lots of different approaches. The height, length and even the materials you use are all up for grabs. However the one piece of advice that appears time and again is about the size of the bed, and in particular, its width.
Since raised beds should never be walked on, you need to be able to reach the middle of the bed when standing or kneeling at the side. Therefore, it is best to keep a bed to a maximum width of four feet (1.2m). Go any wider and you risk the unreachable middle of your raised bed becoming a weed strewn no man’s land.
How to build a raised bed.
Materials for a raised bed
I bought four thick scaffold boards, each one being 6 foot (1.8m) long. I had a 6 foot length of 2by4 in the shed which I cut into four pieces for corner posts. Pretty much any size of corner post will do. old fence posts are perfect. 16 deck screws to join it all together. Deck Screws are designed for outdoor use, so will not rust.
The only other expense was a small tin of wood preservative which I painted on the cut ends to stop the wood from getting damp and rotting.
Lining your raised bed
There is quite a lot of debate about whether adding a plastic liner to the inside of your raised bed will protect the wooden walls. Some say it stops moisture and others say it holds moisture against the wood, speeding up the process of decay. I turned to my favourite RHS gardening manual for advice and they didn’t recommend lining a raised bed. I decided to follow their advice.
Positioning a raised bed
Consider the needs of the plants you will be growing. Do they need full sun or partial shade? Make sure you leave sufficient space to allow you walk around your bed and enough space to crouch or kneel to tend to your crops. Consider whether you are leaving enough of a gap for your wheelbarrow or lawnmower to get through too.
Remove grass. If there is a lawn below your bed, then cut out the turf spade by spade. You do want to ensure the bed is on level ground.If you are on a slope, build up the lower end or dig in to the higher end to give yourself a flat working area.
Raised bed construction
Saw two of the scaffold boards down to 4 feet long. Paint the cut ends with wood preservative allowing the first coat to dry before adding a second coat.
It really is a simple matter of screwing together the ends and sides to the upright posts. Mark with a pencil where you want to put your screw holes. For a neater, more professional look, Mark the positions evenly, centred to the post and evenly spaced top to botttom as per the illustration.
This is the time to consider sanding or planing the top edges of boards if there are kids around who might get splinters.
Drill pilot holes with a small diameter drill bit to ensure the wood doesn’t split. I would also recommend countersinking your holes. This will ensure you never get snagged on a screw end when passing your raised bed.
Checking it is squared
A simple way to square your raised bed is to measure the lengths of each diagonal, going from corner to opposite corner. If both lengths are the same, your bed is properly squared. If the lengths are out, then give the wood a knock and then remeasure. Repeat until perfection is achieved or you say “stuff it, that’ll do”.
Filling your raised bed
Break up and dig over the soil below your raised bed to one spade depth.
Now comes the fun bit. A mix of weed free topsoil and general purpose compost is what you need. Since bags of dirt are sold in litres here in the U.K., let’s do our calculations in metric measurements.
180cm x 120cm x 20cm= 43200 cubic centimetres, or 432 litres of dirt required. Now that is a good volume so ask your supplier about discounts, or create your own compost and save yourself a small fortune.
Shovel it in, rake it flat and your raised bed is ready to be planted.
Why are the posts taller than the edge of the bed?
You can of course cut your posts to be the same height as the scaffold boards. Mine are left longer because when planning our raised bed we couldn’t decide between 9inch high and 15 inch high so that if next year I decide I want a higher raised bed I can just add another level of 6 inch boarding directly to the posts rather than taking the whole thing apart and starting again.
Build a cover for a raised bed
The (very much optional) next step up is to create a cover. You can turn your raised bed into a coldframe or mini-greenhouse.
Hoop based covers are great, lightweight supports for shade netting, bird netting or plastic sheeting. They support a lot of weight in comparison to their size and they are great value too.
The daytime temperature inside the frame, will be between 5 and 15°F warmer than the rest of the garden. Be careful though, because in Summer and even in Spring temperatures can rise high enough to kill off your plants.
What we learned (new for 2021)
The main thing was that cats really like a raised bed. To them it can look a lot like a toilet. That is not so great when you are growing veg to eat. If you find your local cat population visiting your raised beds to make deposits then you will want to do something about it. If you haven’t tried hoops (see above) then you could consider fence of wire mesh to keep them out. It doesn’t need to be particularly stable; just a few bamboo poles shoved in the ground and a roll of wire mesh wrapped around the outside of that.
If you enjoyed this project why not try try something a bit more challenging, such as building your own garden sofa?