Successfully growing herbs in urban planter boxes hinges largely on providing adequate depth for healthy root development. While herbs are generally adaptable, a depth of 6 to 12 inches (15 to 30 cm) is the ideal range for most popular varieties.
Shallow-rooted herbs like chives, cilantro, and thyme can thrive in containers as shallow as 6 inches. Medium-depth herbs, including basil, parsley, and mint, prefer 8 to 10 inches of soil. For larger, more established plants like rosemary, lavender, or bay laurel, aim for a minimum depth of 12 inches to accommodate their more extensive root systems.
Depth alone isn't the only factor. Excellent drainage is non-negotiable; ensure your planter has sufficient holes. Use a high-quality, well-draining potting mix, not dense garden soil. Deeper boxes also retain moisture better, reducing watering frequency. For a mixed herb planter, choose a depth of at least 10-12 inches to accommodate different root needs and ensure all your herbs have the space to flourish, bringing fresh flavors to your urban space.