Cut an 8-inch diameter patio footing tube to the desired height for the garden pillar. These tubes, made of heavy-duty cardboard, are available for purchase at home supply stores.
Place a cement stepping-stone on a flat surface and cover the top surface with two to three layers of plastic wrap. Set the tube in a vertical position on top of the stone. Wrap the plastic around the bottom of the tube. This will hold the concrete inside.
Mix the concrete according to the package instructions to create a mixture with the consistency of pudding. Have a person hold the tube while you fill it with concrete. Cover the top opening with plastic wrap and place a stepping-stone on top.
Dry the concrete pillar for a minimum of two days. Remove the tube from the concrete pillar by tearing it off in sections.
Place the pillar in a protected area to let it cure for a minimum of one week. This will ensure the concrete is dry and hard.
Seal the concrete pillar by painting or spraying on a concrete sealer before using it in the garden. Apply paint or decals to the pillar before sealing, if desired.