For balconies and rooftops, a container garden is one of the only options that you may have to grow plants. Rooftop and balcony containers must be lightweight, yet strong enough to insulate trees and hearty plants through winter. Although containers at a garden center may cost a pretty penny, there is another solution. You can make lightweight, sturdy planters that resemble alpine troughs using a mixture known as hypertufa.
Pull on dishwashing gloves and a breathing mask before working with concrete. Concrete is caustic and can irritate your lungs and skin.
Mix two parts cement and one part peat moss in a plastic bucket.
Pour enough water into the cement mixture that the mix becomes the consistency of a mud pie.
Line the inside of the larger cardboard box with plastic wrap. Stand the four PVC pipe pieces on their ends in the bottom of the cardboard box.
Pack the hypertufa mixture around the pipe pieces to fill the bottom of the box up to a level even with the tops of the pipe pieces.
Place the second box inside the first box so that the bottom rests on top of the hypertufa mixture.
Pack the hypertufa mixture into the space between the two boxes. Mist the exposed hypertufa and the two boxes and cover with plastic. Allow the hypertufa to harden for 48 hours.
Remove the inner cardboard box once the hypertufa has hardened. Mist the hypertufa with water and cover with plastic. Allow the container to cure for another four to seven days.
Remove the outer box and smooth over the rough edges of the container with a wire bristled brush.