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After building the raised bed out of wood, stone or other materials, the most important work follows: filling it. The contents of the bed, carefully layered with various materials, ultimately determine how well the plants cultivated there will thrive and how large the harvest will be. Of course, such a raised bed can also simply be filled with soil, but then as a gardener you forego some of the most important advantages.

A raised bed consists of several layers

When is the best time to fill the raised bed?

Raised beds can be filled both in spring and in autumn, although both times have their very specific advantages and disadvantages. Beds planted in spring benefit from the heat generated by the decomposition processes, raising the soil temperature by a few degrees - with the result that these beds can be planted two to three weeks earlier. At the same time, beds that are only filled shortly before the gardening season have the problem that they collapse after just a few weeks. On the other hand, if the raised bed was built in the fall, you can fill it with filling material throughout the winter: vegetable waste from the kitchen, fallen leaves, grass clippings, shredded wood clippings, bedding from pet cages, hay and straw… the raised bed acts as a kind of composter, holding the materials already decomposed during the winter months.

The different layers of a raised bed

Raised beds are made up of different layers, starting from the bottom up using coarser and then finer material. The individual layers should never be too thick. Grass clippings, for example, are always scattered thinly and loosely in the bed so that nothing sticks together and mold cannot form as a result. Scatter thin layers of semi-mature or mature compost between the individual layers, which inoculates the contents with microorganisms and thus promotes faster decomposition of the material. In addition, the filling with fine layers of soil prevents the formation of cavities inside the bed - this can prevent the raised bed from sinking suddenly and severely.

Structure of a raised bed in the overview

When filling, make sure that the material used is not too dry. A certain moisture - not wetness! - already when filling would be ideal, but can also be achieved if necessary by gently spraying over freshly sprinkled layers.

The first layer

The bottom layer of the raised bed is made up of coarse materials like branches, twigs and even inorganic matter like rocks, rubble or gravel. This first layer is used for drainage and should ensure that excess water can drain away quickly. With the appropriate construction of the raised bed, you can also design this layer with flat stones and larger stone slabs in such a way that smaller animals such as lizards, slowworms or bumblebees find a home here.

The second shift

The next layer consists of basically all green waste from the kitchen and garden: vegetable waste, leaves, grass clippings, sods and weeds you have pulled (but not root weeds like ground elder, couch grass, bryony or bindweed!). If you want to use the raised bed as a cold frame in early spring, add a layer of horse manure about 40 centimeters thick to this layer. But this needs to be tamped down well before you pack any more layers on top. Horse manure is important for cold frames because it develops a lot of heat.

The third shift

This is then followed by several thin layers, depending on what filling material you have at hand: grass clippings, semi-mature compost, animal bedding, leaves, chopped wood, garden waste and the like. Thin layers of mature compost as well as horn shavings (€32.93) and rock flour (€14.13) are placed between the individual layers. These ensure that a particularly valuable and nutrient-rich soil is created from the filled material.

The top layer

The end is always a layer of good potting soil or very mature compost at least 15 centimeters thick. Under no circumstances should this layer of soil be too thin, otherwise the plants cultivated in the bed will not have enough space for their roots and it will then be difficult to grow. When it comes to the question of which soil to use, the answer is basically very simple: decide on a high-quality and humus-rich potting soil, which you can mix with mature compost if necessary. By the way: With bark mulch, you can later mulch the plants in the raised bed and thus reduce weed shoots.

Fill the raised bed with inorganic materials

Instead of coarse plant material, you can also use non-rotting inorganic fillers such as stones and stone residues, crushed stone, grit, sand, gravel, expanded clay (€19.73) or granules (e.g. lava) for the bottom layer. These have the advantage that the bed will not sink so much as a result. However, at the same time the proportion of organic green matter is reduced and thus also the proportion of newly formed soil. As a result, fewer nutrients are available to the plants overall.

tips

Never compost plants in the raised bed that reproduce via their roots or tubers - mint, Jerusalem artichoke and various weeds would strive to reach the surface from the deeper layers and multiply diligently there. Seed weeds such as the orchid, on the other hand, are not a problem, since the seeds and seedlings usually do not survive the high temperatures inside.

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