Abstract
Horticultural production, post-harvest handling and fruit and vegetable processing generate heterogeneous residual streams that are increasingly framed as feedstocks for a circular bioeconomy. Their conversion into agronomic inputs is attractive because it can couple waste prevention with reduced dependence on peat, mineral fertilisers and other virgin resources. Yet the value of a recovered product is determined less by the generic label 'horticultural waste' than by the match between feedstock properties, processing conditions, product quality and agronomic function. This critical narrative review integrates evidence on four principal valorisation routes: waste-derived biostimulants, peat-replacing growing-media constituents, biochar, and nutrient recovery from digestates and related wet residual streams. Literature published from 1 January 2000 to 29 June 2026 was examined using multidisciplinary and agriculture-relevant scholarly sources, supplemented by citation searching and reference verification. The evidence indicates that biostimulant claims are most convincing when effects are demonstrated beyond simple nutrient supply and supported by chemical or biological characterisation; current studies remain strongly batch- and crop-dependent. Compost, vermicompost and processed green-waste fractions can replace part of peat, but performance is governed by air-filled porosity, water relations, salinity, pH, maturity, particle size and pathogen control rather than by renewable origin alone. Biochar can improve physical and chemical properties of media and soils, but feedstock and thermal history create large variability, while polycyclic aromatic hydrocarbons and volatile compounds require quality control. Anaerobic digestion can mobilise nutrients from wet residues, although nitrogen losses, salinity and crop-demand mismatches complicate direct digestate use; fractionation and struvite recovery can improve handling and phosphorus targeting but add processing burdens. Across all routes, the strongest circular strategy is a cascading, function-led system in which clean extractable fractions, fibrous solids, woody residues and nutrient-rich liquids are directed to the least intensive process capable of producing a safe and reliable input. The main research need is therefore not another catalogue of technologies, but multi-batch and multi-site validation linked to standardised product specifications, contaminant control, life-cycle assessment and credible substitution of conventional inputs.