Raised bed made of lightweight concrete

These days, when supermarkets are open nearly around the clock and virtually everything, from bread to vegan fried chicken, can be ordered by mouse click, knowledge about the cultivation of food crops often falls by the wayside. This opinion is also shared by Michael Barde, principal of the elementary school in Melsbach in the German state of Rhineland-Palatinate. “Together with students and parents, we plant our school kitchen garden every spring. The garden is tended by the students, and everyone involved later prepares the harvest to be eaten in the school kitchen.”

This year, the small cereal and potato field in the school garden was supplemented by a raised bed just adjacent. The sponsor was the regional lightweight concrete manufacturer KLB Klimaleichtblock, based in Andernach, Germany. “We are of course very pleased to have the opportunity to support such a fantastic project,” says KLB’s Managing Director Andreas Krechting. The raised bed – consisting of KLB formwork blocks –  was set up in the school yard of the elementary school and already filled with substrate a few days before the main spring cleaning. “We built the raised bed right onsite,” continues Krechting. “But basically anyone could relatively easily build their own raised bed at home.”

Optimal Height

The very practical property of this construction from KLB: the lightweight concrete formwork blocks used are stacked atop each other in several rows. In this way, the height of the raised bed can be easily adapted to the height of the users. It’s important to begin by laying a level layer of lava or crushed stone so that the external walls remain level on a stable foundation.

For a raised bed measuring 1 x 1.50 m – like the one in the school garden in Melsbach – 14 KLB formwork blocks are required for every layer: eight end blocks and six normal blocks each. When constructing the bed, special attention should be paid to forming the rectangular corners. The blocks in the additional layers are then installed in offset to the desired height. “To improve the stability of the bed in Melsbach, we completely filled the three block layers with lava granules. A wire mesh placed at the bottom of the bed, provided with additional permeable grass blocks, keeps out unwanted rodents. A bubble sheet placed on the inner wall of the bed serves as insulation.  When subsequently filling the raised bed with substrate, care should be taken that the bottom-most layer consists of especially permeable material to prevent waterlogging. Lava granules, for example, are suitable here. The middle layer is topped with garden waste or green clippings. This ensures that the plants when first planted, and during the vegetative growth stage, are provided not only with additional nutrition, but also release the so-called heat of decomposition upward. The top layer in the raised bed is formed of plant soil or, ideally, of an especially beneficial lava-pumice substrate.

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