How do I Create Concrete Containers for Gardening?

Concrete is made from cement combined with organic materials or stone.

Concrete is made from cement combined with organic materials or stone.

Concrete supplies a sturdy material for creating permanent garden containers. Concrete is a combination of cement and other materials, such as peat or gravel. Hypertufa, a concrete made by adding peat moss and sand to cement, works well for garden use because it's easier to work with, while also providing a look more similar to natural stone compared to other types of concrete. You can shape the concrete to fit almost any design or to match existing landscape elements.

Creating Planter Molds

Any flexible, waterproof item can make a good container mold. A cardboard box lined in a plastic bag works well for both large and small pots. You can also use thin-walled plastic pots or bowls, although you may need to line them if they have holes. If you use a more rigid container for a mold, select one with a wider opening than bottom so the concrete pot can slide out more easily. You can also line the interior with a bag to help slide out the finished pot. Hypertufa releases easily and works like clay, so you can form it to the mold interior without the need for a secondary mold insert.

Mixing It Up

Concrete hypertufa pots are made from a mixture of peat moss, Portland cement, and sand, vermiculite or perlite. Combine two parts of sifted peat moss with one part cement powder in a large bucket. Mix in 1 part of vermiculite, sand or perlite, depending on your preference or what you have on hand. Mix in one part water thoroughly, or enough water to evenly moisten the batter to the consistency of thick oatmeal.

Putting It All Together

The concrete mixture is thick enough to form to the inside of your mold almost like modeling clay. Pack the bottom of the mold first, making it about 1 ½ inches deep for 1-gallon and smaller containers, or up to 3 inches for larger containers. Continue to form the concrete up the interior walls of the mold, keeping the side thickness the same as the bottom thickness. Pots require drainage, so insert one or more ½-inch wooden dowel plugs into the concrete in the bottom to form drainage holes.

Finding the Cure

Curing ensures the concrete hardens completely. After forming the pot, cover it tightly with plastic sheeting or bags. The pot must cure in the mold for one to two weeks at temperatures no lower than 50 degrees Fahrenheit, and preferably over 55 F. Concrete requires moisture to fully cure, so mist the pot with water if the surface moisture evaporates. After the initial cure, you can remove the dowel plugs and slide the pot from the mold. Continue to cure it for an additional two to three weeks before using it. Curing it in an area exposed to rainfall or sprinklers will provide moisture, which aids curing and helps leach out excess alkalinity from the pot.

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