Rather than go out and spend a fortune on store-bought planters, make your own stylish concrete flower planters at a fraction of the cost. Transform a balcony, deck or patio with your own handmade concrete container garden. Concrete planters are especially good for top-heavy plants, because they do not tip over or dry out as quickly as a plastic pot does. Concrete flower planters also make great personalised gifts for your gardening friends.
Select two sturdy cardboard boxes to use as moulds. The centre box needs to fit evenly within the larger box to create a planter with 5 cm (2 inch) walls. If you decide to make a planter bigger than 60 cm by 60 cm (2 feet by 2 feet), the walls need to be 7.5 cm (3 inches) thick.
Set up close to a water source in a shady area of your yard, where your finished planter can cure for three weeks. Spray the boxes with the mineral oil or spray lubricant to aid in their removal later on.
Pour dry concrete mix into your wheelbarrow. Add water gradually and mix until just moistened to the consistency of thick mud. Squeeze the mixture in your hands to test that it is neither dripping wet nor crumbling apart.
Using a shovel, fill the bottom of your larger box with 5 cm (2 inches) of concrete and pack it down. Centre your smaller box inside the larger box to create the mould for the sides.
Using the shovel and trowel, gradually scoop concrete mixture into all four sides and use a tamper to compact the concrete as you go. Smooth and level the top edge when full.
Cover with plastic and cure in the mould for 36 hours. Carefully pull away the cardboard boxes to release the concrete planter. Smooth out any rough edges with your stiff wire brush.
Add texture or design to the outside planter walls by carving with a screwdriver or other sharp tool, if desired. Handle the planter carefully at this stage because the concrete has not fully hardened. Leave planter outside in the shade for three weeks to finish curing.
Spray your cured flower planter with your garden hose to rinse thoroughly. If you want to add drainage, do so by drilling holes in the bottom or filling the bottom with pottery shards or pebbles.
Embellish dry concrete planters by gluing marbles, broken pottery, tile, pebbles or trinkets onto the cured concrete planter using epoxy, liquid nails or grout. Decorate your cured concrete planters with latex or oil-based paint if desired.
Add colour or stain to wet cement, if you like. Pour concrete mix over a mound of sand to make a rustic round planter. Shop at yard sales, thrift stores and flea markets and salvage yards to find plastic or thin metal containers to use as moulds. Styrofoam is also a good material for building moulds. If you build a wood form, caulk the seams and line bottom and sides with plastic so the concrete will not seep into cracks.
Wear gardening gloves to protect your hands from the chemicals in concrete mix. Do not pour concrete when rain is expected that day. Do not pour concrete in temperatures below 10 degrees Celsius (50 degrees Fahrenheit).