Up to 44% of EU residents are exposed to noise levels that are detrimental to health. In this context, vertical gardens could play an important role in architectural acoustics, where the main absorber material is the substrate soil. Plants have a beneficial effect for higher frequencies when planted in a large density. In this paper a vertical garden design developed at the Pontificia Universidad Catolica of Ecuador (PUCE) was tested for interior acoustic design. The modules solely with substrate and planted with ferns were tested. The objective was to ascertain and explain the random incidence sound absorption coefficient of vertical garden modules. 50 modules making up a total floor area of 10.125 m2 were used for the measurements. Six different configurations were measured: connected versus dispersed and directly on the floor versus with an air cavity of 5 and 10 cm. Furthermore, each configuration was tested with modules solely filled with substrate and with substrate filled modules with densely planted ferns. The weighted random incidence sound absorption coefficient of the modules densely planted with ferns equals 1.00. This applied to all different configurations tested. The sound absorption coefficient in the lower frequencies (100-315 Hz), mid frequencies (400e1250 Hz) and high frequencies (1600-5000 Hz) was 0.59-0.80, 1.00 and 1.00 respectively. This makes this type of building technology highly suitable for applications where sound needs to be attenuated, paving the way for applying vertical garden systems as a design tool for improving the acoustics of indoor spaces or urban squares.