For your new urban planter box, it's best to avoid using regular garden soil. While it might seem convenient, garden soil is typically too dense for containers. It compacts easily, restricting crucial oxygen flow to plant roots and leading to poor drainage, which can cause root rot. Garden soil may also harbor weeds, pests, and diseases.
A special potting mix is formulated for success in containers. These blends are lightweight and fluffy, often containing ingredients like peat moss, coconut coir, perlite, and vermiculite. This structure ensures excellent drainage and aeration while still retaining moisture and nutrients where roots can access them. For planter boxes, a high-quality "container mix" or "raised bed mix" is ideal. You can also create your own by combining equal parts compost, coconut coir (or peat moss), and perlite. This provides a nutrient-rich, well-draining environment that will give your urban plants a strong, healthy start and support vibrant growth throughout the season.