Octagonal Raised Garden Bed

Materials
Treated plywood
2x4s or similar
Screws
No more nails adhesive
Black plastic
Staples
Duct tape

Tools
Table saw
Screwdriver (preferably electric)
Staple gun
An extra set of hands or clamps

These beds are 1930mm (76") in diameter.
Cut eight pieces of plywood. I cut mine to 800mm x 300mm (about 31.5" x 11.8“). The size does not have to be exact as long as they are all the same. This picture shows wider pieces which made up the center bed of a mandala garden.

Cut the joining pieces to 300mm or the same height as the plywood. I used left over decking timber.

The angle between each of two piece of plywood is 135 degrees. Set the table saw up to 45 degrees and cut that part off. That is waste, use the 135 degree piece to join the plywood together.

Run a squiggle of adhesive on one side of the 135 degree angle of a piece of timber.

Place a piece of plywood on the timber with the adhesive on it, screw together. Do this to each side of four pieces of plywood.

After you have four sets of sides made up, follow the same steps of gluing and screwing to attach each of the other four pieces of plywood. Due to the large size and angles, there is no really easy way to do this. It helps to have a level floor such as a garage to assemble the parts on.

One finished bed.

Three in a stack.

Cut long strips of plastic and wrap around, covering both sides.

Using a staple gun loaded with short staples, staple the plastic to the plywood.

We taped all the edges with black duck tape which isn't waterproof. After several years the tape has started to pull off. I just wait until dry weather, dust off the dirt and squirt adhesive onto it to re-stick.

If you only have one bed, put it anywhere. We had seven and laid them out with string attached to the center bed. You can see the peg in the middle of this bed. We had to fiddle a little to make them look even and also allow enough room to walk between them.

Here they are in position.

We drove in pegs to hold them in position. Once filled with soil they weren't going anywhere anyway. Our ground is a mixture of clay and river stones of all sizes up to soccer ball size which accounts for the angle of some of the pegs.

The raised beds are finished but I wanted to show how we put in edging, laid out weed mat and filled a path around the octagonal beds with limestone chips.

Here's a shot of our vegetable garden the following year. There is corn in the front bed and a runner bean teepee in the larger middle bed. The two Ts with wires in the background that look like a clothesline are supports for kiwi fruit. The fence all around is to keep out wekas, native swamp hens that love pulling up everything.

The corn has moved counter clockwise as the crops rotate.