This is a common concern for urban gardeners. The direct answer is: it depends on the plant and your planter box construction. Most common annual vegetables and herbs have fibrous root systems that are unlikely to cause structural damage to sturdy, well-built planter boxes. However, aggressive or large perennial roots, like those from some trees, shrubs, or vigorous vines, can potentially warp wooden boxes or exploit existing cracks over time.
To prevent potential damage, consider these tips. First, choose the right plants for containers. Opt for varieties known for compact root growth. Second, ensure your planter box is constructed from durable, rot-resistant materials like cedar, high-quality plastic, or metal, and that it has adequate drainage holes. Third, for long-term plantings, installing a root barrier liner inside the box can provide an extra layer of protection. Finally, regular maintenance is key. Monitor your boxes for signs of stress, such as bulging sides or persistent moisture, and repot or divide plants that become root-bound.
In summary, with proper plant selection, quality materials, and basic precautions, you can enjoy a thriving urban garden without fear of your planter boxes being compromised by roots. The benefits of gardening far outweigh this manageable risk.