Evaluation of Different Combinations of Ornamental Perennials for Sustainable Management in Urban Greening

Ornamental perennial plants play a strategic role in reducing green areas' management costs, keeping the ground, sparing water, and avoiding weeds. The aim of this research is to evaluate the growing performances of seven combinations of six different ornamental perennial herbaceous species and their role in weed containment under low-maintenance conditions. The experiment was performed for three years (2019-2021) in an open field. The selected species were Hemerocallis "Stella de Oro" (A), Phedimus spurius (M.Bieb.) "t Hart 'John Creech" (B), Tulbaghia violacea Harv. (C), Phlox subulata L. "Trot Pink" (D), Potentilla neumanniana Rchb. (E), and Gaillardia "Kobold" (F). Four replicates for each combination were tested (28 plots, 4 m² each): AB, CD, EF, AB + CD, AB + EF, CD + EF; AB + CD + EF. No watering or fertilization was performed during the cultivation period. Each year, from April to November, three manual weeding activities were performed and the dry weights of the weeds' aerial parts were measured. The ground cover performance was evaluated through digital image analysis using the mobile device application Canopeo. Dry aerial perennial biomass variations between the end and beginning of the experiment were calculated. As a result, CD showed the best performance for weed containment (0.5 g m^-2 weed dry weight in the third year), ground cover (63.1% and 64.3% of plot coverages during the second and third years, respectively), and producing ornamental biomass (4316.8 g m^-2). The highest total dry amount of harvested weeds was shown by AB + CD + EF (1114.6 g m^-2), demonstrating that combinations with a higher number of species were less efficient in avoiding weeds. The research allowed us to identify the best combinations to always keep the soil covered and to improve the ornamental and environmental values of urban green spaces under low-maintenance regimes.