DLG-tested quality for your crop success

For successful cultivation - whether at home in the balcony box or in horticultural seedling production - a consistently high product quality of the growing substrates is indispensable. For the development of a new testing framework for neutral and independent quality testing of planting and potting soils, the DLG experts have used other physical, chemical and biological parameters of growing substrates that are relevant for the user, in addition to the legal requirements, for example, from the German Fertiliser Ordinance (DüMV).

For the physical properties, the filling quantity for packaged goods and the weight by volume are tested in the same way as the dry substance and particle size distribution. Especially the so-called "oversize grain" is crucial here: As potting soils are made to a certain extent from compost, unrotted components can disturb the homogeneity of the growing substrate. Here, a maximum limit of five percent of the volume applies for grain sizes over 20 mm.

Chemically, the most important soluble macro and micro-nutrients are analysed and the planting soils are checked for compliance with the limits for possible contamination with heavy metals and harmful substances. Salinity and pH are also among the parameters determined in the laboratory.

Finally, the planting and potting soils must also be free of important human pathogenic germs, such as salmonella or moulds, and may only contain a maximum of three germinating weed seeds or sprouting plant parts per litre of substrate. The most important test, however, is that for plant compatibility: Substances harmful to plants in the seedling test are a "no-go".

Continuous monitoring and unannounced product sampling

By participating in DLG seal of quality tests, a manufacturer commits to permanent neutral monitoring of product quality by the DLG. For this purpose, several unannounced monitoring samples are taken and analysed annually by trained samplers at the manufacturer's or at the retailer's premises.