Yes, a wooden urban planter box can rot after a couple of rainy seasons, especially if the wood is untreated or poorly protected. The risk depends on the wood species, how the box is built, how much water it receives, and whether water can drain away freely. In a rainy climate, the wood will repeatedly get wet and dry out slowly, which creates ideal conditions for fungal decay. End grain, joints, the inside of the box, and the bottom edges are usually the first places to show problems.
Some woods are naturally more resistant to moisture and decay. Cedar, cypress, teak, and black locust tend to last longer than softwoods such as pine or spruce. Pressure-treated timber can also perform well, but you should confirm that it is suitable for growing edible plants if that is your intention. Even rot-resistant wood will eventually suffer if it sits in water or is constantly damp.
Good drainage is essential. A wooden planter should have drainage holes, a slight gap under the base, and a liner or inner pot that keeps soil from pressing directly against the timber. Raising the box off the ground helps air circulate and prevents the bottom from staying wet. Using a well-draining soil mix and avoiding overwatering also reduce the chance of rot.
Protection makes a major difference. Wood sealing, painting, or oiling the box can slow water absorption, but the coating must be maintained. Pay special attention to cut ends and joints, because these areas absorb water quickly. Reapply a suitable waterproof finish every year or two, and repair small cracks before they become traps for moisture.
Watch for soft spots, dark stains, mould, crumbling wood, or a musty smell. If you notice these signs early, you may be able to dry the box, improve drainage, and treat the affected area. In general, an untreated wooden urban planter box may begin to deteriorate after a few rainy seasons, while a well-built, rot-resistant, sealed, and properly drained box can last many years with regular care.