Bottom Ashes from household wood firings –garden fertiliser or better subject to disposal?

Bottom ashes from wood firings are from 100 % organic and natural sources if fresh wood is used. The ashes are rich on nutrients such as potassium, lime, phosphorous, sodium and therefore might be perfect suitable as fertiliser for private gardens or as additive to enhance private biowaste and greenery composts. In context of the IZES-project "EmMA"[1], bottom ashes from different firing systems for wood biomass (pellets, logs, wood chips) were chemically analyzed. As a result, values for parameters for heavy metals such as chromium VI and total, zinc and molybdenum, etc. were elevated and above threshold defined by the German Federal Fertilizer Ordonnance (DüMV[2]) or Federal Soil Protection Ordonnance (BBodSchV[3]) for direct use as fertiliser. Therefore, without pre-treatment or quality assurance system in place, the direct and uncontrolled application of bottom ashes for fertilisation purposes should be avoided and for private households, with low quantities annually, a save waste disposal option should be used. Within ReNu2Farm quality standards for RDFs will be defined to maintain high quality organic fertilisers which comply with national and European laws.


[1] EmMA – Secondary emission reduction devices for wood firing systems below 1 MW, 2016  - 2019, funded by the German Federal Ministry of Food and Agriculture, FKZ: 22402415

[2] DümV: Düngemittelverordnung vom 5. Dezember 2012 (BGBl. I S. 2482), die zuletzt durch Artikel 1 der Verordnung vom 2. Oktober 2019 (BGBl. I S. 1414) geändert worden ist.

[3] BBodSchV: Bundes-Bodenschutz- und Altlastenverordnung vom 12. Juli 1999 (BGBl. I S. 1554), die zuletzt durch Artikel 126 der Verordnung vom 19. Juni 2020 (BGBl. I S. 1328) geändert worden ist

Share this

Tweet Share