In Europe, food and agricultural waste amount to millions of tonnes annually. Effective management and valorisation of these residues result in environmental benefits and foster opportunities within the circular economy. Composting has emerged as a sustainable method to convert waste into fertiliser, enhancing soil fertility, water retention, and crop resilience against diseases. However, an adequate compost production process is vital to obtain a functional fertiliser. In this study, a controlled conditions self-produced compost from horticultural waste (C1) was compared against two other commercial composts, one of similar vegetable origin (C2) and another from chicken manure (C3). Physicochemical parameters and nutrient contents in the three compost types were analysed, and phytotoxicity and plant development tests were carried out on Lolium multiflorum Lam. seeds and Pistacia lentiscus L. seedlings. C1 presented fertility and germination parameters similar to C3 and showed the best seedling development. In contrast, C2 showed low levels of fertility, germination, and plant development because of impurities and possible substances inhibiting plant growth, suggesting inadequate compost formation processes. Finally, C3, although it presented germination data similar to C1, produced the worst results in the development of seedlings, probably because of high salinity values and low phosphorus content.