The chelate assisted phytoremediation of polluted soils, based on the complexation of metals with chelators, can be a valuable green solution for agricultural soils decontamination. Copper is considered a hardly available and slowly translocating element, but the complexation may increase its bioavailability and translocation capacity, with benefits for soil phytoremediation. In our study, the ability of horse manure - a natural source of compounds which can act as chelators for enhancing the bioavailability and uptake of copper from contaminated soils - was investigated, by the use of white mustard (Sinapis alba) as the accumulator plant; the results were compared with those obtained for ethylenediaminetetraacetate (EDTA), a synthetic chelator. The copper bioavailability, bioaccumulation, uptake, and thus the potential for phytoremediation of copper polluted soils, were estimated by translocation factor, bioaccumulation factor, and uptake coefficient. The results indicated that the use of horse manure as natural chelators source can improve the copper phytoextraction capacity, also having the advantage of an increase in biomass.