When creating an urban herb garden, container depth is crucial for healthy plant development. Most popular culinary herbs thrive in planter boxes with a depth of 6-12 inches (15-30 cm). This range accommodates the root systems of common herbs like basil, cilantro, chives, and oregano.
Shallow-rooted herbs such as thyme, marjoram, and creeping rosemary can flourish in containers as shallow as 6-8 inches. Medium-depth herbs including basil, parsley, and mint prefer 8-12 inches for optimal root establishment. Only a few herb varieties like lovage and angelica require deeper containers beyond 12 inches.
Drainage is equally important - ensure your planter boxes have adequate drainage holes to prevent waterlogged soil. Use quality potting mix specifically formulated for containers, as garden soil becomes too compacted. For mixed herb plantings, maintain the 12-inch depth standard and group herbs with similar water requirements together.
Consider the mature size of your chosen herbs when planning container spacing. Most herbs need 6-12 inches between plants. Regular harvesting encourages bushier growth, and consistent moisture without overwatering will keep your urban herb garden productive throughout the growing season. With proper depth and care, your planter boxes can yield abundant fresh herbs even in limited urban spaces.