You have a lot of options, when it comes to building a raised bed, not only in terms of construction material, but also size and shape.
The most common options for materials are:
Railway sleepers: These can be found on classified listings websites and generally sell for around £15 each, depending on size and shape.
Decking boards: Easy to get a hold of and transport, can be found at most garden and DIY stores. They range from around £3 – £10 each.
Clip together plastic boards: These are probably the simplest way of constructing a raised bed and they last many years too, but the time saved will be made up for in cost.
Old wood: Reclaimed wood, spare and cutoffs are a favorite of allotment users everywhere.
The option you go for is really down to you, they all require tools to do the job, other than the plastic clip together. So if you’re not comfortable using an electric drill, saw or screwdrivers, then that’s the option for you.
Recommendation: Don’t be silly and build this in the snow (if it can be avoided). Not only is it cold, but also the wood being wet will give a weaker grip for the screws than if it’s dry, I will be adding some extra screw when the wood drys out, to strengthen the structure.
I much prefer going for wood, I love the look of it in the garden and I enjoy putting them together. For this example construction, I’m using decking boards, as it’s a cheaper option than railway sleepers. As I need to build 7 of these beds, I really need to think about costs.
The first thing to do is think about the shape and size, you want the bed to be. You need to ensure that you’re going to be able to reach every part of it, as you want to be able to plant and weed the entire bed. I’m making a walkway to my greenhouse from these beds, so that’s what decided the the width for me, it needs to fit at the side of the greenhouse door, without going onto the path. I kept the length the size of the original boards, this ensures all the edges are perfectly straight and saves me some cutting time.
So, measure up and mark all the boards that need cutting. It is a good idea to have some left over or spare wood you can attach to the corners, which can be dug into the ground for extra support.
I have used off cuts for the corner supports, these are going to be screwed onto the main bed prior to putting them into the ground. They need to be strong enough to keep it in place and support all the boards once your bed is filled with soil/compost.
So lets begin. First of all, get two of your 4 corner supports and your chosen wood for the main bed. I’m going 3 decking boards high, so I need 3 of my widths. These are now screwed into the corner pieces to create your first side, I put two, 2 inch screws in both sides of each board.
Repeat this process to create your second width side.
Now you want to attach your long boards to the two sides. If you have someone who can give you a hand with this, it certainly makes it easier. I leaned one of the sides against a chair and my partner held the other side, while I screwed in the first board, again putting two, 2 inch screw in both ends of each board.
Attach all of your boards for your chosen height (in this case 3), then carefully turn the whole thing over and attach the rest. Make sure they are all flush against not only each other, but the width sides too. You will risk not only having a slanted raised bed, but also one where soil and water can easily escape, if you don’t get this right.
Once the boards are all attached, you’re done. Simply dig some holes where your feet supports are going to be, place your bed, burying the feet and fill.