There are few studies combining ornamental sunflower cultivation with aspects of plant nutrition and soil fertility, so it is necessary to carry out research in this area in order to determine the parameters of fertiliser sources that are best suited to this crop. After analysing the nutrients and toxic elements contained in the aquatic macrophyte Egeria densa, it was found that there is potential for its use as an organic fertiliser and that the dried and partially decomposed macrophyte showed physical characteristics similar to those of commercial substrates, making it possible to use it in ornamental sunflower production and making it a sustainable alternative.