Metal planter boxes are an attractive alternative to standard plastic or wood planters. Many come embossed with a variety of designs, and the metal takes on an interesting patina over the years. Rust is the main issue with most metal planters. The constant contact with moist soil over long periods of time may lead them to rusting through. Liners are sold with some planters, but if you already own a metal planter without one, an alternate method of lining it is necessary.
Clean the inside of the planter with a wire brush and water if it has been used before. Remove any soil residue. Rinse a new planter to remove any dust that may be on the inside. Dry completely after cleaning.
Paint the inside of the planter with a lead-free asphalt paint. Paint a single coat on, taking care not to paint over any drainage holes in the bottom of the planter. Asphalt paint protects it without chipping off and adding toxins to the soil.
Paint with a second coat of asphalt paint once the first coat is dry. Shine a flashlight into the planter, looking for any areas that were missed with the second coat and touch-up as needed. Allow both coats of paint to dry overnight.
Fill the planter with your preferred potting mix and plants. Water regularly to keep the soil moist, as metal planters heat up and dry out more quickly.