This is a common and excellent question for urban gardeners. The short answer is: it depends on the specific planter box and the type of tomato plant. For successful growth, the depth of your planter is crucial for healthy root development, water retention, and nutrient uptake.
For most small tomato varieties, such as patio, dwarf, or cherry tomatoes, a minimum soil depth of 12 inches (30 cm) is generally recommended. However, 18 inches (45 cm) or more is ideal. This deeper volume allows roots to spread, supports a more stable plant, and reduces the frequency of watering.
Many decorative urban planters are quite shallow, perhaps only 6-8 inches deep. These are unsuitable for tomatoes, which will become stunted, stressed, and produce poorly. Before planting, always measure the internal depth of your box, not just its exterior height.
If your box meets the depth requirement, ensure it also has adequate drainage holes. Use a high-quality potting mix, not garden soil, and consider compact or "bush" type varieties labeled as suitable for containers. With sufficient depth, proper care, and the right plant choice, you can absolutely enjoy homegrown tomatoes from your urban planter boxes.