The invention relates to a process for removing contaminants and nitrogen and phosphorus compounds from plant waste water using ornamental plants selected from the group of plants suitable for cutting, including in particular Chinese aster, as purification plants.Callistephus chinensis, Dahlia sp., Canna indica, Cymbidium sp., Paphiopedilum sp, Rosa sp., Chrysanthemum sp, Iris sp, sunflower (Helianthus annus), Strelitia reginae, Anturium sp balcony tomato (Lycopersicon lycopersicum), whose root system allows wastewater to be treated for 2 to 3 weeks. The treatment plant consists of an insulated tank filled with a granular substrate, in which the plants are planted and properly rooted with a surface density corresponding to their natural surface density at most, and has an inflow of contaminated water and an outlet of pre-treated water preferably with a pump.