Starting your first urban herb garden is exciting! A common and crucial question is about planter box depth. The good news is most popular culinary herbs don't require extremely deep soil. For a successful harvest, aim for a planter box depth of 6 to 12 inches (15 to 30 cm).
This range accommodates the majority of herbs like basil, cilantro, oregano, thyme, mint, and chives. Herbs like parsley and rosemary, with slightly deeper root systems, will appreciate the deeper end of that range, around 10-12 inches.
Depth is just one factor. Ensuring excellent drainage is non-negotiable. Your planter must have holes at the bottom. Use a high-quality potting mix, not garden soil, to ensure proper drainage and aeration for the roots. For larger, woodier herbs like a mature rosemary bush, consider a deeper container, up to 16 inches.
A simple rule: match the depth to the plant's mature root size. Shallow planters (6-8 inches) are perfect for compact herbs and windowsills. Deeper boxes (10-12+ inches) offer more root space, better moisture retention, and flexibility for mixing herbs. Start with the 6-12 inch guideline, ensure good drainage, and your urban herb garden will be off to a fantastic start