The GARDENA gardening expert
Great question, Mr. W., as according to the popular opinion, eggshells are a natural product and therefore, degradable! But, it actually reacts differently.
Eggshells are a mineral composition of the chicken ovary and are therefore not an organic substance. In this respect, the eggshell is not immediately decomposed by the soil flora. As a mineral product, it is subject to the same chemical-physical weathering process as the soil, for example with lime stone. This is also the reason why the eggshell can be found in the compost for some time until at some point, it becomes crumbly, coloured by humic substances and is no longer noticed.
Another totally different aspect in this context, one that is decisive, is the compost hygiene. Eggshells not only do not belong in the compost because they do not rot there, but rather also because the eggshells bring the danger of salmonella to the compost.
Salmonella clings to every type of poultry egg. As a living bacteria, salmonella does not generally rot in the compost but rather likes to multiply there. Through the distribution of the compost in the beds and finally in the garden soil, the salmonella could possibly make its way onto vegetables eaten raw, strawberries or low-hanging berries on shrubs. The danger is uninteresting until something happens. But from a horticulture scientific perspective, the salmonella danger in this context is real.
Only those who cultivate their compost in the so-called “hot rotting” phase allow the compost to disinfect itself through the warm rotting phase and destroy any potential salmonella therein. But: What do I want with components, such as eggshells in the compost when they do not decompose and as a result, must be sifted out?
Throw the eggshells preferably in the organic rubbish, Mr. W., because there, they enter the hot rotting phase – or directly in the refuse bin.