Potential use of recycled stone wool substrate granulate as substrate component

Product properties of used stone wool substrate products can add extra value to other (organic) substrates thereby deserving a second life as part of a circular economy. The chemical and physical product characteristics of this reusable substrate granulate (RSG) and mixes with peat were investigated according to the French norm for growing media and the metal leaching requirements defined in the European Union EcoLabel for Growing Media. Water retention curves were established. Hydration efficiency and contact angle measurements were carried out on these mixes to evaluate their wettability. Strawberry plant development was evaluated for substrates containing RSG material. The RSG product can be incorporated in an organic soil improver according to the French norm and complies with EU EcoLabel metal leaching requirements. Even more than their physical qualities, the increase in wettability by RSG addition can be considered as the main added value of RSG. Risk of hydrophobicity can be annihilated with RSG addition. Cultivation of strawberry plants using RSG containing substrates resulted in positive plant development and an equal fruit yield compared to a peat:bark mix.