We had our Corten products tested for food safety by an independent institute and received certification in 2021. This was important to us because we use the material among other things for herb spirals and raised beds and do not want any harmful substances in food. Random tests of our products in the laboratory have not found any limit values to be exceeded.
As is so often the case, there may be a potential health risk if the material is used improperly - unfortunately we cannot rule this out.
To explain: The patina on Corten contains small amounts of chromium, copper and nickel, which can possibly pass into the soil if the basic barrier layer is not formed. Studies show that Corten is harmless as long as the barrier layer can form in peace. Once the barrier layer has formed, the material can be used in the garden without hesitation and the cultivation of edible plants is absolutely safe.
A regular alternation of wet and dry in a period of approx. 21 days is normally enough to form the base layer. The barrier layer is fully formed after 2-3 years. This means that you have to give the herb spiral about a month to form the base layer before you plant it.
As soon as the base layer cannot form, e.g. if the alternation between wet and dry does not take place in the outdoor area, heavy metals can (but do not have to) dissolve from the steel and possibly be released into the soil as hazardous substances.
Heavy metals occur naturally in nature and in most gardens, and can also enter any garden soil via the rain, for example. The decisive factor here is again the limit values.
For all those who are unsure about Corten despite certification, we offer a galvanised version in the same design for most articles. With galvanised versions, we can absolutely exclude potential releases of heavy metals. Iron, which can be released from galvanised steel to the soil, is even a valuable mineral that benefits plants and us humans.