Concrete blocks allow great variety
Concrete is not only an inexpensive, but also a very versatile material. You can use exposed concrete for the construction of a raised bed and thus perhaps create an interesting contrast to the naturally designed garden. However, there are also a number of concrete blocks that are externally modeled on natural stones. With their roughly hewn visible side, broken edges and different colors in a natural look, such stones also look very pleasing in a natural garden.
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Dry stone and mortar walls
Another advantage of concrete - in addition to its price and its variety - is its significantly lower weight compared to natural stone. This comes into play when building walls, for example when a raised bed is to be built on a slope. For high natural stone walls you need very large and heavy stones for static reasons alone. Accordingly, the edges of the bed are very thick, so that there is hardly any bed area left. You can also build both dry stone and mortar walls from concrete blocks, with mortar walls in particular being placed on a frost-free concrete foundation. The heavier the construction, the deeper and stronger the foundation has to be built. In addition, an inner film is always recommended for mortared walls,so that the mortar joints do not become porous and therefore flexible due to the constant moisture.
System blocks made of concrete / lightweight construction systems
So-called system stones are easier to install, thanks to the grooves they practically hook into one another to create stable walls. Since these are hollow stones, you can build very high walls thanks to their low weight. To make the hollow blocks heavier and therefore more stable against internal pressure, you can also fill them with crushed stone, gravel, grit (€ 12.80 on Amazon *) or sand. The manufacturers always give instructions about the wall height from which a mortar foundation or special adhesive must be used between the stones. If in doubt, ask a specialist for static calculations. If you want to build curved raised beds, you can use concrete blocks with a conical shape. These make it easy to build curves.As with dry stone walls, you can now and then build wider joints so that they can be planted or used as a shelter for small animals.
Inexpensive manhole rings
Parts of manhole pipes made of precast concrete can also serve as raised beds and have a practically unlimited lifespan. In addition, such raised beds can be set up quickly and easily - you only need to move one or more manhole rings of the appropriate size to the desired location, fill and plant them. However, you need a machine for transport - for example a small excavator - because they are very heavy and unwieldy. Smaller rings can also be rolled to the location by hand if you let them unload vertically. There are manhole rings at building material dealers in many different sizes and with different diameters, whereby only rings up to 150 centimeters are practical - up to this size you can just reach the middle of the bed.Manhole rings can be stacked in the groove system so that you can build the raised bed at the desired height. In addition, since they are impermeable to water, you do not need any foil.
Tips
Concrete slabs can also make a stable raised bed wall. For example, you can simply place high concrete pavement slabs upright in a bed of dry mortar - the raised bed is ready. Concrete palisades can be dug upright into the ground and thus form a stable bed frame.
