Construction of a raised flower bed garden is similar to building a wall or solid fence. It provides the bed with a better source of drainage and allows the gardener better access to the plants. Decide which materials to use before building the raised bed. Concrete blocks and wooden sleepers can be used to build the bed walls. Consider what shape and height you want the beds and think about clear access to the plants.
Level the area where the raised bed is going to go. The area must be free from weeds and debris. Spread a 1/2 inch layer of hard-core over the levelled area. A hard-core base will firm the ground and is made from grit and gravel.
Compact the hard-core with a shovel or rent a compactor from a tool rental store. A compactor will mash down the hard-core to form a solid base.
Mark where the bed walls are going to go with building chalk or string.
Lay a thin layer of wet mortar over the marker if using concrete blocks. Lay the wooden sleepers, or large wooden blocks, on the marker, if you are using them. Build the wall up to the required height with mortar between each block or dig a hole into the ground for wooden poles at the four corners of the bed. Make sure they are straight and level, then anchor them to the sleepers using long screws .
Check that the blocks or wooden sleepers are level all the way around the raised bed. Allow the concrete to dry for 24 hours if using concrete blocks.
Paint or plaster the outside of the flower bed and allow 24 hours for either material to dry.
Fill the bed with topsoil and use required plants.
Hire a concrete mixer if raising large areas.
Use protection when handling concrete mix as it is an irritant.