Choosing the right finish for wooden planter boxes intended for edible plants is crucial for your health and your garden's success. The key is to select products that are non-toxic and specifically labeled as "food safe" once fully cured. Avoid conventional exterior paints, stains, or varnishes, as they can leach harmful chemicals into the soil and be absorbed by your plants' roots.
For optimal safety, consider these recommended options. Raw or boiled linseed oil (from flaxseed) is a classic, natural choice that penetrates wood deeply. Ensure it is 100% pure without added chemical driers. Specialty "salad bowl" finishes, designed for direct food contact, are another excellent and durable option. Natural beeswax or a beeswax-mineral oil blend offers a simple, waterproofing coating. For color, use milk paint, a biodegradable paint made from natural ingredients like casein and lime.
Always apply any finish to the exterior and top rim of the planter only, avoiding direct contact with the interior soil. Line the interior with a heavy-duty, food-safe plastic barrier (like HDPE) to create a protective layer between the treated wood and the soil. This practice, combined with a food-safe finish, ensures a beautiful and healthy harvest from your urban garden.