When creating a vibrant urban garden with planter boxes, getting the depth right is crucial for the health of small shrubs and ornamental grasses. Generally, a depth of 12 to 18 inches (30 to 45 cm) is recommended for most small shrubs. For ornamental grasses, which can have surprisingly deep root systems, a depth of at least 12 inches is a good starting point, with 18-24 inches being ideal for larger varieties.
The specific depth needed depends on the mature size of the plant. Dwarf shrubs like boxwood or compact hydrangeas often thrive in 12-inch deep planters. For ornamental grasses such as Blue Fescue or Fountain Grass, a 12-inch depth is usually sufficient. However, for larger grasses like Miscanthus, a deeper planter of 18 inches or more is necessary to accommodate their extensive root systems and prevent them from becoming top-heavy and tipping over.
Proper drainage is non-negotiable. Ensure your planter boxes have adequate drainage holes to prevent waterlogged soil, which can lead to root rot. Use a high-quality, well-draining potting mix to provide the right balance of moisture retention and aeration. By selecting the correct planter depth and ensuring excellent drainage, you can create a thriving miniature landscape on your balcony, patio, or rooftop.