## 1 Introduction  
The ornamental plant sector has globally undergone a significant increase in recent years, both in terms of production and demand, and its further development is expected, especially in Europe, over the next decade [1]. Similarly, the production of hardy ornamental nursery stocks has steadily increased over the last 40-50 years [2; 3], and it is now considered of great importance throughout Europe, reaching an economic value of approximately EUR 20 billion per year since 2010 [4]. In particular, the Netherlands leads the European table with more than 5 billion EUR/year derived from the production of plants and flowers, followed by Italy, Germany, France, and Spain. In Italy, Pistoia (43\({}^{\circ}\)54\({}^{\prime}\) N, 10\({}^{\circ}\)41\({}^{\prime}\) E. 30 a.s.l. ), near Florence, is considered the greatest plant nursery district, playing a prominent role with about 1000 ha of container-grown plants [5]. Currently, most of the substrates used in potted plant production are peat-based [6; 7; 8; 9], but environmental concerns about peat-lands [10] due to intense peat mining [11; 12] have led researchers and stakeholders to explore alternative and more eco-friendly materials as potting mixes [13; 14; 15]. In recent years, raw or composted waste by-products, such as mushroom compost [2], paper mill sludge [2; 16], almond shell waste [17], and coir (or coconut fiber) [18; 19] were tested as a total or partial alternative to peat moss in the growing media, with variable results in terms of growth and quality of plant production. Amongst them, one of the most interesting waste by-products is represented by dredged marine and river sediments [20; 21; 22; 23; 24]. Although the micro- and macro-nutrient contents of dredged sediments make these matrices a good candidate as peat-free growing media, the presence of high levels of hydrocarbons and heavy metals limits their recycling in agriculture [22]. The application of low-cost biological technologies (e.g., co-composting) can reduce the organic as well as the inorganic contamination and improve the physical, chemical, and biological properties of dredged sediments, making a suitable substrate for plant growth [25; 26]. However, the remediated sediments are not currently included in the European and Italian regulations as fertilizers or agronomic substrates [27], although the efficiency of dredged sediment recovery and recycling has been widely demonstrated. Moreover, the evaluation of the effect of peat's partial or total replacement with a waste material in terms of CO\({}_{2}\) emissions and other environmental concerns became a relevant goal. Life Cycle Assessment (LCA) is a technique widely used to evaluate the environmental impact of a production system or product itself [28], and it is considered a helpful methodology for defining and quantifying greenhouse gas (GHG) emissions and other environmental impacts [5; 29]. LCA has already been used in several agricultural systems, considering either the entire life cycle (\"cradle to grave\" approach) or only a stage of the process (e.g., \"gate to gate\") [30; 31; 32; 33; 34]. Therefore, the research hypothesis was to verify whether peat could be replaced by waste products in the pot nursery industry without compromising plant growth and increasing CO\({}_{2}\) savings. The present study expands and completes our preliminary research [35] about the suitability of dredged river sediments (S) composted with agricultural green waste (GW) as a replacement growing media for ornamental plants as part of the Life project AGRISED (LIFE17 ENV/IT/269). Different ratios of S and GW were tested to remediate sediment contamination and optimize their management, following Italian and European legislation. Once the co-composting phase was completed, a one-year cultivation phase was performed to evaluate the effect of sediments assembled with these waste by-products on the growth of two ornamental container-grown shrubs (i.e., _Photinix fraseri_ Dress. and _Viburnum tiinus_ L).