The results on the selected biometric and mechanical properties of common reed Phragmites australis and reed sweet grass Glyceria maxima were presented. The experiments were conducted with the help of the universal testing machine Instron 5966. The underground biomasses, diameters, tensile forces, displacements and tensile strengths for summer and winter rhizomes of both species were assessed and compared. The final results indicate that rhizomes of common reed had higher values of the studied parameters of biometric and stretching than sweet reed grass rhizomes. Therefore, there are more opportunities to use them to protect the coastline.