For urban gardeners looking to grow small vegetables like lettuce, the ideal depth for planter boxes is typically 6 to 8 inches (15 to 20 cm). This depth provides sufficient room for lettuce roots to establish themselves while allowing for proper drainage and nutrient absorption. Leafy greens such as lettuce, spinach, and arugula have relatively shallow root systems compared to larger vegetables, making them perfect candidates for container gardening in limited spaces.
When setting up your urban planter boxes, consider these key factors: Ensure adequate drainage holes at the bottom to prevent waterlogging, use quality potting mix rich in organic matter, and maintain consistent moisture levels without overwatering. The 6-8 inch depth allows for healthy root development while being shallow enough for easy placement on balconies, patios, or rooftops.
For continuous harvest, you can succession plant lettuce every 2-3 weeks. This depth also works well for other compact vegetables like radishes, green onions, and certain herbs. Remember that while depth is important, the width of your planter boxes also matters - provide at least 6-8 inches between plants for proper air circulation and growth. With the right depth and care, you can enjoy fresh, homegrown lettuce throughout the growing season.