Soak the ball in water for several hours. Take it out, set it aside and let it drain. Cut the stems off the roses, leaving 1/2 inch on the bottom.
Hot glue the Styrofoam block into the container. Low temperature glue works the best and won't melt the Styrofoam.
Push stick into the base of the ball stopping 3/4 of the way through.
Poke small holes into the oasis ball for each rose. Put the stem of the rose in the hole. Push a greening pin into the base of the flower to secure it to the ball. Continue adding flowers until the ball is covered.
Make your topiary as full as you want by adding extra flowers or adding leaves or ivy between the buds. Put moss on the Styrofoam base by using greening pins to hold it in place. Embellish it with ribbons and trimmings.