Don’t lose your marbles—show them off! Spread a layer of tile adhesive over the outside of a terra-cotta pot using a putty knife. Make sure it’s thick enough to hold the marbles in place. Press the marbles into the adhesive, and let dry. Mix grout to the consistency of peanut butter. Working quickly, fill in the spaces between the marbles. Once the grout begins to set up, remove any excess from the marbles with a damp sponge so the grout doesn’t adhere permanently.