The simple answer is yes, taller urban planter boxes generally require more soil and water than shorter ones. The primary reason is volume. A taller box has a greater capacity, meaning it needs more soil to fill it. This larger soil volume acts as a bigger reservoir for both nutrients and moisture.
However, the relationship isn't always perfectly linear. Watering needs depend heavily on what you plant. Deep-rooted vegetables in a tall box may need less frequent watering than thirsty shallow-rooted plants in a shallow box, as the deeper soil retains moisture longer. The key factor is the root zone. A taller box provides a deeper root zone, which can store more water, but it also means you must water thoroughly to reach the entire root system.
Drainage is crucial. A tall box with poor drainage can lead to waterlogged soil at the bottom, harming roots. Always ensure adequate drainage holes. While taller boxes use more resources initially, they can promote healthier plant growth and offer more stable moisture levels, potentially reducing watering frequency for established plants. For efficiency, choose a box depth suited to your plants' root needs and always check soil moisture a few inches down before watering.