For a thriving small herb garden in an urban setting, the depth of your planter boxes is crucial. Most popular culinary herbs, such as basil, cilantro, chives, mint, and oregano, have relatively shallow root systems. A depth of 6 to 8 inches (15 to 20 cm) is generally sufficient for these herbs to grow healthily.
However, for optimal growth and to accommodate a wider variety, aiming for a depth of 8 to 12 inches (20 to 30 cm) is highly recommended. This extra space allows for better root development, improved moisture retention, and more stable soil temperature. It's especially beneficial for herbs like parsley, rosemary, and thyme, which can develop deeper roots.
Key factors beyond depth include ensuring excellent drainage with holes at the bottom and using a high-quality, well-draining potting mix. Avoid garden soil, as it compacts in containers. With the right depth and care, your compact urban planter can yield a bountiful and fragrant herb harvest all season long.