Crumple and bunch the plastic grocery bags together into a mound shape, forming the rough size and shape of the boulder seat you desire.
Mix the quick-setting concrete according to the package instructions, ensuring it reaches a thick, paste-like consistency.
Pour the mixed concrete over the bunched plastic bags, covering them completely and smoothing the surface with a trowel or gloved hands to create a textured appearance.
Allow the concrete to set and cure completely, following the instructions on the concrete mix packaging for curing time.
Once cured, carefully peel away the plastic drop cloth and move your new boulder seat to its desired location in your garden.
For a different look, experiment with adding color to the concrete mix using concrete dyes or pigments to match your garden’s color scheme. You can also adjust the size and shape of the boulder seats by varying the amount of plastic bags used and the way they are bunched together. Consider creating a set of seats in varying heights and sizes to add visual interest and functionality to your garden seating area.
