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A raised bed saves space, is easy to care for and promises rich yields. In order for it to work, however, it depends on the right raised bed filling.
In a nutshell
- Raised beds are built in layers from the bottom up
- Upward, each layer is created from finer, more rotted material
- If a layer is made too thick, the function of the layers below it will be restricted
- The lower layers in particular must be created carefully, as they cannot be reached later
- Depending on the materials used, raised beds have different lifespans from one to several years
The raised bed filling
The grown soil has a highly heterogeneous structure in several layers. It thus fulfills a wide variety of functions that are essential for the growth of plants. Instead, raised beds only have the layers you plan to use when you create them. In order for a raised bed to function ideally as a plant base, you should heed the following procedure layer by layer when building up the raised bed filling.
Notice: The layers described are built up one after the other from bottom to top. This means that layer 1 is also the first step towards the finished raised bed filling.
location 1
- What: protective grille
- With what: vole grid, rabbit wire, other permeable metal meshes with a mesh size of 1 to 2 centimeters
- How: Lay flat on the floor and attach to the side walls all around (e.g. tacks or clips)
- How much: single layer
- Why: against invading animals such as mice, rats, dormouse etc.
location 2
- What: rough pruning
- Material: Various material such as branches, waste from hedge cuttings, etc. in different lengths of 30 to 50 centimeters
- How: Insert prunings in alternating orientations, avoiding large holes or voids
- How much: 20 to 30 centimeters
- Why: as a drainage layer against waterlogging and rot, as well as for better ventilation in raised beds
location 3
- What: fine pruning
- With what: chopped branches, shredded perennials, chaff
- How: Apply to a large area as a loose fill on a rough cut, using finer material from bottom to top
- How much: 15 to 20 centimeters
- Why: as a flat support on the rough wood cut, against giant fine components of the level above
Tip: Instead of fine wood clippings, long grass clippings are also suitable. However, this rots faster and develops a significantly more inhibiting effect on ventilation. However, grass clippings impress with their high proportion of nitrogen, which will sooner or later benefit the planting.
location 4
- What: coarse organic decomposition material
- With what: manure, coarse compost
- How: Apply loosely as a closed layer
- How much: 20 to 30 centimeters high
- Why: as a nutrient base, especially nitrogen
Tip: The layer of manure or compost also generates heat in addition to the nutrients due to the progressive decomposition. This heat is a kind of natural frost protection for sensitive plant roots, especially in the transitional periods. However, this heater can hardly be regulated or "refilled".
location 5
- What: fine decomposition material
- With what: fine, heavily decomposed compost, grass clippings, animal bedding
- How: as a flat substructure of the later plant layer, ideally several different materials in layers
- How much: around 10 centimeters
- Why: as a supplier of a wide variety of nutrients, such as nitrogen, potassium and phosphorus
location 6
- What: plant layer
- With what: garden soil or plant substrate, e.g. mixture of soil and humus
- How: as a top coat on previous layers, rich and full-surface
- How much: at least 10 to 15 centimeters
- Why: as the actual growth layer for all plants under consideration
Attention: It is true that one reads again and again "to the top" for the final substrate layer with regard to the layer thickness. However, if the substrate layer is too thick, the underlying layers of the raised bed filling can no longer contribute effectively to the functioning. Instead, choose the bottom ventilation layer so thick that the following layers can be dimensioned as specified.
Here you can download the PDF for the ideal raised bed filling. This means you always have a helpful guide to hand when setting up your raised bed.
When to create?
If you have carefully followed the structure of the layers in the raised bed, the question may now arise as to whether all the loose parts will sink in over time. Indeed it is. In particular, the very loose, coarse layers will initially settle and decrease in thickness after watering or intensive irrigation. Depending on the plant, this can cause a significant problem if the fine root networks are damaged in the moving soil. So that plants used do not suffer from these changes, you should proceed in such a way that you create the raised bed, ideally in autumn or winter. Then the materials can settle and the bed is available for safe planting in the spring.
frequently asked Questions
What is the layered structure of the bed for?If you fill your bed completely with potting soil, it will rot quickly due to a lack of ventilation. And the water balance can also be disturbed, so that you have to reckon with waterlogging.
If the layers are too coarse, can the entire structure compact over time?Yes that's right. A raised bed has a limited shelf life as the materials used will continue to rot and compact into a compact mass as they decompose.
What do I do if I'm missing a rough hedge trimming, for example?In principle, there are several ways to reach the goal in every position of the bed structure. If you are missing coarse branches and twigs, you can create an alternative drainage and ventilation layer with straw or even pebbles, for example.
Can I refill a sunken raised bed?Refilling is possible to a certain extent. It is important that the lower layers are still intact for ventilation and drainage. Fresh manure or compost is usually added to the penultimate level. To do this, after the end of the planting period, half of the top layer is pushed aside, the manure is installed and then the second side is filled in the same way.
How long does a raised bed last?It is not possible to give an exact indication of the usability of a raised bed. Depending on the materials used, but also the size of the raised bed, the construction can usually be used for several years without any problems.