Climate impacts of bio-based horticultural substrates: Life-cycle assessment of individual components and multi-crop blends

Reducing greenhouse gas (GHG) emissions from horticultural growing media (GM) is critical due to the high climate impact of peat extraction and use. Peatlands are major carbon reservoirs, and their excavation and use releases substantial amounts of CO₂, while also causing habitat loss and biodiversity decline. Bio-based alternatives, including extruded wood fibers, aged bark, various composts, degassed agricultural fibers from anaerobic digestion, and willow-derived biochar, offer potential for climate-friendly peat substitution.

This study quantified the cradle-to-use GHG emissions of individual bio-based GM components and six stakeholder-defined multi-component blends designed for strawberry, basil, Kalanchoe, and Buddleia, using life cycle assessment (LCA) with the ReCiPe 2016 Midpoint method. The functional unit was 1 m³ of substrate. The LCA included raw material production, pre-processing, transport, mixing, and substrate use. Economic allocation and system expansion were applied where production generated co-products.

Results indicate that individual bio-based components can reduce carbon footprints by more than 50% compared with pure sphagnum. Multi-component blends with partial to full peat substitution showed GHG reductions of approximately 45–90%, depending on the proportion and type of bio-based constituents. These findings highlight the substantial potential of bio-based growing media to lower greenhouse gas emissions while maintaining suitable physical, chemical, and biological properties for horticultural production.