Table of Contents
- composition
- grit
- humidity
- Calculation example
- overview
- frequently asked Questions
Potting soil is sold by the liter rather than by weight. Sometimes it is necessary to know how heavy the soil in pots is because of the bearing capacity of the subsoil.
In a nutshell
- Grain and composition affect weight
- Dry weight of potting soil is less than wet weight
- to calculate the weight, the density of the substrate and the volume of the vessel must be known
composition
How heavy potting soil is depends on its composition. Fibers are often added to substrates, making them lighter and more permeable. Average substrates consist of a mixture of 50% compost, 25% plant fibers and 25% coarse-grained parts such as brick chips or lava granules. A little fertilizer is already added to most commercially available substrates. This means that it is not necessary to fertilize in the first few weeks.
Notice: To protect the bogs, when buying substrates, make sure that they do not have any peat contain. Substrates with peat also favor pests such as fungus gnats.
grit
The granulation and the resulting density is also a factor that also affects the weight of potting soil. substrates or Components in substrates with a coarse grain or structure do not have a high density and are therefore often not as heavy. Substrates with a fine grain have hardly any air spaces, which means that they have a higher density and are therefore heavier. You can find out for yourself with a simple experiment. A bucket of sifted compost is heavier than a bucket of unsifted soil because there are more spaces and not as much soil can fit in.
The density of solids is easy to calculate. It is the mass divided by the volume. For some substrates such as sand or gravel, the density can often be found in tables provided by gravel works and can be used when calculating the weight of substrates.
Examples of the density of substrates:
- garden soil: 830 kg/m³
- Raised bed soil: 1.4 t/m³
- Gravel (0 - 4 mm grain size): 1.4 t/m³
- Sand (0 – 2 mm grain size): 1.5 t/m³
- Lava granules (8 - 16 mm grain size): 1.1 t/m³
Notice: Density ratio also equals weight per liter. 1 ton per cubic meter would correspond to 1 kg per liter.
humidity
Hardly any substrate is 100% dry, because the humidity ensures a certain residual moisture. The residual moisture can only be determined using suitable measuring devices.
There are basically five different categories of substrates:
- dry
- scrawny
- fresh
- wet
- wet
Calculation example
Knowing the density of the potting soil, you can easily calculate how heavy the soil is in a pot if the volume is also known.
If a substrate has a density of 600 kg/m³ and the pot in which the substrate is filled has a volume of ten liters, the volume of the pot must first be converted. Ten liters correspond to 0.01 kg/m³. If the density is added to the volume, the result in this example is a weight of 6 kg that is in the pot.
Notice: If the potting soil loses moisture, the total weight can also drop slightlyn.
overview
| crowd | dry weight | 20% moisture | 40% humidity |
|---|---|---|---|
| 1 liter | 0.38kg | 0.45kg | 0.53kg |
| 20 liters | 7.4kg | 8.88kg | 10.36kg |
| 40 liters | 14.8kg | 17.76kg | 20.72kg |
| 50 liters | 19kg | 22.8kg | 26.6kg |
| 60 liters | 22.8kg | 27kg | 31.8kg |
| 70 liters | 26.6kg | 31.92kg | 37.24kg |
frequently asked Questions
Yes, there are special substrates for roof gardens, for example, which are significantly lighter than normal potting soil. This is a mixture of crushed bricks and compost. Occasionally some sand or clay is also added. On average, depending on the composition, the weight is between 1/3 and half that of conventional substrates. The substrate is suitable for both vegetables and ornamental plants.
It depends on the composition and how compacted the substrate is. However, you can determine this with a so-called flow experiment. Fill a liter of soil into the pot with a drainage hole. The pot is then raised so that the hole is free and placed in a bucket. Pour 1 liter of water slowly and evenly over the surface. Measure the residual water and the difference between the liter and the residual water is the amount of water that your substrate can absorb.
Yes, that is possible. To do this, use 50% compost and mix in 25% coconut fibers. You can vary the remaining 25%. Expanded clay or lava granules, for example, are suitable. For plants that like stony soil, you can also use sand or mix in gravel. However, you should make sure that the plants tolerate calcareous rock. If this is not the case, you should preferably use lava granules. You can add horn shavings or horn meal as fertilizer.
