Compost is a valuable recycled fertilizer that returns organic waste to the production process and promotes soil fertility. For use in horticulture and agriculture, compost must not contain any pathogens or substances harmful to plants. Compost can contain phytotoxic substances if it is too fresh or if started to rot/ was stored without control.
The phytotoxicity of a compost can be tested using the open and closed cress tests. While the open cress test serves as a rough indicator, the closed cress test indicates even low toxicity of the compost because the plants also come into contact with gases from toxic compounds.
It is advisable to carry out both tests, as the open cress test does not always indicate that the compost is compatible with the plant.
Cress tests are a simple tool to test the phytotoxicity of composts. They are easy to carry out and analyse, and they only require few materials.