PVC Pipe Planter Disney world does this! Lowes sells the 4 to round PVC pipe with holes already drilled. Purchase an end cap, fill with rock, soil, and plant. I will often put these in the center of a very large pot to stabilize, and add amazing heigh
How to Make a Petunia Tower -- Basically, it's a ring of galvanized fencing lined with landscape fabric, then filled with potting soil. The petunias were planted through slits in the landscape fabric. This looks like a pretty easy do-it-yourself project!