Place the biggest pumpkin of the 3 on your work table as it will serve as the base. Then, remove its stem.
Using the glue gun, attach moss, leaves, and flowers on the side.
Insert three floral stakes near the place where the stem used to be.
Remove the stem of the second pumpkin.
Place the second pumpkin on top of the first one and push until the stakes are all the way in.
Glue the remaining moss and leaves to the side.
Insert floral stakes as described in step No. 3.
Place the remaining pumpkin on top of the other 2, but do this without removing its stem.
You can decorate the third pumpkin too, or just leave it as it is, and place your new pumpkin topiary on the table.