Concrete is a durable medium for creating garden containers. Concrete containers can help trees, shrubs and other plants to survive cold winters by providing protection from cold. Additionally, concrete garden pots last longer than plastic or terra cotta. However, concrete isn't always a good choice for gardening on balconies, due to the weight of the container. The answer may be hypertufa. Hypertufa combines concrete with organic materials such as peat moss to create a lightweight container that resembles tufa stone, a soft stone with a spongy consistency.
Mix three parts peat, three parts concrete and a handful of fibers. Add water and stir with a trowel until the mixture is the consistency of a mud pie or cake batter. Put on gloves and a mask before you begin.
Place the larger box on the ground or a flat working surface. Put a concrete block on the ground on each side of the box to reinforce the sides.
Cut the PVC into 4-inch rounds that are 2 inches long. Place the rounds flat-side-down onto the bottom of the box and space them equidistant from one another.
Scoop the hypertufa mix into the bottom of the box around the PVC rounds. Fill the box until the hypertufa mix is level with the top of the rounds.
Place the second box inside of the first box on top of the rounds and center it so that there is equal space on all sides.
Scoop the hypertufa mix into the space between the two boxes. Push the mix down so that it completely fills the space between the boxes. Gently tap the sides of the box to dislodge air bubbles.
Cover your container with a piece of plastic sheeting and wait 36 hours for the hypertufa container to cure. Remove the cardboard boxes from the container. Add texture to the planter and smooth rough edges with a wire brush. Allow the planter to dry another three weeks.