The warm, natural look of wood is a perfect complement to urban gardens, but its durability is a valid concern. The short answer is: yes, wood in planter boxes will eventually decompose, but the speed depends entirely on the wood type, construction, and maintenance.
Not all woods are equal. For longevity, choose naturally rot-resistant species like cedar, redwood, or cypress. These contain oils and tannins that repel moisture and insects. Pressure-treated lumber is another durable, though more chemical-intensive, option. Avoid woods like pine or fir unless they are specifically treated.
Construction is key. Ensure excellent drainage with multiple holes at the bottom to prevent waterlogging. Using a liner can protect the inner walls, but ensure it doesn't block drainage. Elevating the planter slightly off the ground improves air circulation.
Regular maintenance dramatically extends life. Apply a non-toxic, water-repellent sealant or stain designed for outdoor use, reapplying every one to two years. Avoid letting soil constantly press against untreated wood.
With the right choices and care, wooden planter boxes can be a beautiful and durable feature in your urban oasis for many years, gracefully aging to a charming silvery-gray patina if left untreated, or maintaining their rich color with proper upkeep.