Growing lettuce in an urban planter box is a fantastic way to enjoy fresh, leafy greens. The number of heads you can fit depends primarily on the box's dimensions and the lettuce variety. For a standard planter box about 24 inches long, 12 inches wide, and 8-12 inches deep, you can typically grow 4 to 6 full heads of lettuce if you aim for proper spacing.
Spacing is the most critical factor. For most heading varieties like Butterhead or Romaine, provide 8 to 12 inches between plants. For loose-leaf varieties, which don't form tight heads, you can plant more densely, spacing them 4 to 6 inches apart. This means you could fit 6-8 loose-leaf plants in the same standard box.
To maximize space, consider a "cut-and-come-again" approach with leaf lettuce. Sow seeds densely across the soil surface. Once the leaves are a few inches tall, you can harvest the outer leaves repeatedly, which extends your yield without needing to thin plants to a single head's spacing.
Ensure your planter has adequate drainage holes and is filled with a high-quality potting mix. Place it in a location that receives at least 5-6 hours of sunlight daily. Water consistently to keep the soil moist but not soggy. With the right spacing and care, a single urban planter can provide a continuous, compact supply of fresh lettuce right on your balcony or patio.