•Wood chips from spruce were mixed with calcium hydroxide to raise the pH.•Three piles (250 m3) with 0, 1.5 and 3.0% Ca(OH)2 have been stored for 4 months.•Storage characteristics and cultivable members of the microbiota were investigated.•Ca(OH)2 was able to decrease the dry matter loss significantly.•The additive led to 5 °C higher maximum pile temperatures (sanitization effect). The objective of this study was to investigate the effect of an alkaline additive on the storage of wood chips from Norway spruce forest residues. Piles of untreated and calcium hydroxide treated wood chips (250 m3) were set up and investigated for four months. It was demonstrated that adding Ca(OH)2 to moist wood chips decreased the dry matter loss by 6%. This was attributed to the increase of the pH to a level of 8, rendering the habitat less suitable for fungal colonisation. The results suggest the set-up storage strategy as a potential alternative method for preserving wood chips when long term storage is required.