One advantage of peat moss/cement planters, also called hypertufa planters, is that you can make them yourself and save a lot of money compared with buying large planters at the garden store. Another is that you can make them any shape you want. And thirdly, they are lighter than planters made of just cement or of other materials such as bricks or natural stone. Finally, they blend in well with grass, plants and trees, making them an integral part of your landscaping design.
Select a mould for your planter. A mould can be almost anything from a cardboard box to a basketball cut in half to a bucket. Styrofoam, wood boards, plastic tubs or a hole in the ground also work. If your mould is made of metal or wood, line it with plastic, or the cured hypertufa planter will be impossible to remove from the mould. For these instructions, the mould will be made from two cardboard cartons, one about 4 inches smaller than the other in width and depth.
Put on rubber gloves and goggles, and then sift the peat moss through a sieve to get rid of clumps and sticks. Put into the wheelbarrow or large plastic container 2 parts Portland cement, 3 parts peat moss and 3 parts perlite. Add 1 cup of reinforcing fibre to each 5 gallons of mix. Mix the dry ingredients, then add water and mix with your hands. Pick up a handful of the wet mixture and squeeze it. If the ball of mixture sticks together and holds its shape, and only a couple of drops of water are released when you squeeze it, then the mixture is the right consistency.
Cover the bottom of the larger box with a 1- to 2-inch layer of the mixture. Center the smaller cardboard carton inside the larger and pack the mixture firmly between the two boxes to the height that you want.
Leave the planter in place during the first stage of curing, which should be 14 to 36 hours, depending on temperature and humidity. Cover the planter with plastic. The second stage of curing begins when you test the side of the planter and find that you can scratch it with a screwdriver, but not with your fingernail.
Remove the planter from the mould, being careful not to break it. Roughen the top edges and corners with a stiff wire brush. Place the planter in a shady spot and let it cure for three weeks.
Fill the planter with water and let it drain out through the porous material. Refill the planter whenever it is empty. Repeat the process for about 10 days. This removes the lime that was in the Portland cement. Drill several holes into the bottom of the planter to improve drainage. Use an electric drill and 3/8-inch masonry bit.
Hypertufa can also be used to make birdbaths and stepping stones. Turn over a flat-bottomed hypertufa planter and it can be a side table on the patio. Make large hypertufa containers near where you will use them. They are lighter than concrete, but still heavy.
You must use straight Portland cement for this project, not premixed concrete or mortar that contains Portland cement as one ingredient.