Not every raised bed needs a concrete foundation - as a rule, a solid and level surface is completely sufficient. However, if the raised bed is to be built in brick (regardless of whether it is a drywall or a mortared wall), a solid concrete foundation is essential for safety reasons.
The more stable the subsoil, the more durable the raised bed
The ground must always be solid and level
The subsoil for a raised bed - regardless of whether it is made of wood, metal or stone - must offer sufficient stability, but should still be sufficiently permeable - this serves to avoid waterlogging in the bed. Especially in newly created gardens, where fresh topsoil has often been poured in, the subsoil must first be compacted. This can be done with a rammer from the hardware store or by hand. On the other hand, if the ground has grown, you can create a level by digging a shallow pit. Make sure that no thick tree roots stretch across this area - these endanger the stability. If in doubt (and if the roots cannot be removed) it is better to choose another location.
Protection against voles and Co.
Of course, the raised bed is not set up on the bare ground. Here annoying rodents such as voles can work their way into the raised bed, causing considerable damage there. To prevent this, you should lay rabbit or chick wire between the ground and the raised bed box. Cover the wire with a thin layer of grit (€46.95) or sand and if necessary lay a weed mat (€21.70) over it - this is particularly useful when the soil is infested with stubborn root weeds. Instead of the close-meshed wire, you can also lay perforated bricks, but there should not be any large gaps between the bricks.
Concrete foundation for stone raised beds
A raised bed will of course be more stable if you set it up on a concrete foundation. Such a base is particularly useful for heavy stone raised beds to ensure stability. But wooden raised beds can also be stabilized with a point foundation. Only the cornerstones stand in a concrete foundation. However, if your raised bed needs a proper foundation, you will need to find other ways to drain excess water from the raised bed - in this case, the bed walls should have adequate drainage options, otherwise the plants will suffer from the accumulated water. Such drainage options arise, for example, through holes in the stone wall (this can be done very well with dry stone walls!) or an artificial drainage system, such as through drain pipes that are routed to the outside.
tips
A layer of pebbles placed between the ground and the raised bed box not only protects against rodents and weeds, but also serves as drainage.