Metal trough planters are a popular choice for gardeners seeking a durable, ready-made container with a distinctive aesthetic. These repurposed livestock watering tanks offer an elevated gardening solution that minimizes bending and provides immediate control over the soil environment. Converting a stock tank into a successful planter requires specific preparation steps to ensure plant health and the longevity of the metal container.
Understanding Trough Materials and Safety
The metal troughs commonly used for gardening are constructed from galvanized steel, which is coated with a protective layer of zinc. This galvanization process bonds the zinc to the steel, creating a barrier that prevents rust and corrosion. The primary concern for gardeners is whether this zinc coating is safe for growing food crops, and the consensus is that it is safe for most plants. Zinc is a naturally occurring micronutrient required by plants, and any small amounts that leach into the soil will likely be absorbed as a nutrient.
Zinc leaching occurs more rapidly when in contact with highly acidic materials. Gardeners should avoid using extremely acidic soil mixes or planting acid-loving plants like blueberries directly against the metal. Before adding any soil, thoroughly clean the inside of a new trough to remove any oils, metal shavings, or manufacturing residues. A simple scrub with warm water and mild soap, followed by a thorough rinse, prepares the surface for its new function.
Physical Preparation and Drainage
The most important physical modification is adding sufficient drainage holes to prevent waterlogging and root rot. Since these containers are designed to hold water, they lack the necessary outlets for excess moisture to escape. To ensure adequate drainage, drill multiple holes across the entire bottom surface, not just a single hole in the center. A good guideline is to create four to six holes per square foot of the bottom surface area, which provides uniform moisture escape.
Drilling galvanized steel requires the correct tools and safety precautions. Use a sharp, metal-specific drill bit, typically between 1/4 and 1/2 inch. Flipping the trough upside down provides a stable surface for drilling, and using a center punch helps keep the drill bit from slipping. The process creates small, sharp metal shavings, so wearing thick gloves and eye protection is necessary. After drilling, run a file or sandpaper over the edges of the new holes to smooth any remaining burrs, and ensure all metal fragments are swept away before moving the trough to its final planting location.
Setting Up the Growing Medium
After the trough has been cleaned and the drainage holes are established, the next stage involves setting up the internal growing environment.
Using a Liner
A liner made from heavy-duty landscape fabric or plastic sheeting can serve multiple beneficial purposes. Lining the interior creates a barrier between the soil and the metal, which helps to slow the natural corrosion process of the galvanized steel. If you use a liner, ensure that it does not block the newly drilled drainage holes. Many gardeners use a layer of screen or mesh over the holes before adding the liner to prevent soil from washing out.
Adding Filler Material
For particularly deep troughs, which can be expensive and heavy to fill entirely with potting mix, a filler material can be used in the bottom third of the container. This technique involves using bulky, slow-decomposing organic materials like wood chips, or non-organic materials such as upside-down plastic bottles or crushed aluminum cans. This filler layer reduces the volume of potting mix needed while providing a stable base and promoting good air flow. A layer of landscape fabric should be placed over the filler material to prevent the growing medium from settling into the voids below.
Choosing the Planting Medium
The final layer is the planting medium itself, which should be a lightweight container potting mix rather than dense garden soil. Garden soil compacts easily in a container environment, leading to poor drainage and suffocating plant roots. A good potting mix is specifically engineered with materials like peat moss or coir, perlite, and vermiculite. This creates an ideal balance of aeration and moisture retention, allowing roots to breathe and flourish.