Cement pots are favored for their sturdy, classic aesthetic and durability, offering a robust option for gardeners, particularly for larger outdoor plantings. Whether they are suitable depends on understanding their unique material properties and taking specific preparatory steps before introducing soil and plants. The main challenge lies in the chemical and physical characteristics of the material itself.
The Impact of Cement on Soil Chemistry
The primary concern with using cement pots for gardening is their highly alkaline nature, which can drastically alter the soil’s chemistry. Cement contains calcium compounds, such as calcium hydroxide and calcium carbonate. When water is introduced, these compounds leach out of the pot walls and into the potting mix. This process elevates the soil’s pH level, often pushing it toward an alkaline range of 8.0 or higher.
Since most plants prefer a slightly acidic to neutral pH (6.0 to 7.0), this creates a significant problem. In highly alkaline conditions, essential micronutrients like iron, manganese, and zinc become chemically “locked up” and unavailable for the plant roots to absorb. Plants requiring acidic soil, such as blueberries, azaleas, and gardenias, will quickly develop nutrient deficiencies marked by yellowing leaves (chlorosis). Species that tolerate higher pH levels, including many succulents and Mediterranean herbs, are better suited for unsealed cement containers. Gardeners should monitor the soil pH with a testing kit.
Physical Properties: Porosity, Weight, and Drainage
Cement pots possess distinct physical characteristics that offer both advantages and disadvantages in a gardening context. The sheer weight of the container provides excellent stability for large, top-heavy plants or those placed in windy locations. This mass ensures the planter remains firmly in place, unlike lighter plastic alternatives.
The material is also somewhat porous, falling between the high porosity of unglazed terracotta and the non-porous nature of plastic. The walls of an unsealed cement pot can wick moisture away from the soil, causing the medium to dry out faster. This evaporative cooling effect can help protect roots from overheating in extreme sun, but it necessitates more frequent watering.
Adequate drainage is paramount, and the thick walls require generously sized drainage holes to prevent waterlogging. If drainage is insufficient or clogged, the material’s thickness can hold standing water, leading to root rot. While the porosity allows for some air exchange, it is less breathable than terracotta, meaning gardeners must be diligent about managing moisture levels.
Essential Steps for Successful Use
To overcome the chemical and physical limitations of cement, proper preparation of the container is necessary before planting.
Curing the Pot
New pots must first be “cured” or “seasoned” to remove the most aggressive, soluble alkaline compounds. A common method is to soak the container in water for several days, changing the water daily. Alternatively, fill the pot with a dilute acidic solution, such as vinegar or a weak fertilizer mix, for about a week.
Applying a Sealant
After curing, the most effective step to prevent long-term pH issues is applying an interior sealant. A barrier, such as a concrete-specific sealer or pond-liner paint, should be applied to the interior walls of the pot. This sealant prevents calcium compounds from leaching into the soil and eliminates the pot’s ability to wick moisture away. This helps maintain a stable soil pH and consistent moisture level.
Ensuring Drainage
Finally, ensuring proper drainage will prevent the most common issue of overwatering and root decay. It is advisable to use large drainage holes, and to cover them with a screen or a piece of broken pottery before adding soil. This prevents the potting mix from washing out and clogging the exit point, which is especially important in sealed pots where the walls cannot facilitate moisture evaporation.