Yes, you can use urban planter boxes for aquatic plants if you seal them properly, effectively creating a charming container water garden. The key is achieving and maintaining a watertight environment. Not all materials are suitable. While plastic, fiberglass, or metal planters often work well, wooden boxes require meticulous sealing. For wood, use a non-toxic, waterproof pond liner as your primary barrier. Alternatively, apply a specialized fish-safe pond sealant to the interior, ensuring multiple coats and complete coverage, especially at corners and seams.
Once sealed, the setup differs from standard planting. Do not use soil, as it will cloud the water and promote algae. Instead, use a layer of aquatic planting media or small, smooth gravel to anchor the plants' roots. Choose aquatic plants wisely: submerged oxygenators like Anacharis, floating plants like Water Lettuce, and marginal plants suitable for shallow water, such as Dwarf Papyrus or Corkscrew Rush, are excellent choices. Avoid large water lilies unless the planter is very large and deep.
Place your aquatic planter in a location with appropriate sunlight for your chosen plants. Maintenance involves topping off evaporated water with dechlorinated water and removing any decaying plant matter to keep the water clean. With correct sealing and care, a repurposed planter box can become a serene, miniature aquatic ecosystem for your patio or balcony.