There is no single weight, because an urban planter box is a system: the empty container, the growing medium, moisture, drainage layers, and plants all add up. A useful rule of thumb is: filled weight ≈ container weight + (media volume in liters × media density in kg/L) + plant/root weight. For wet potting mix, use about 0.7–0.9 kg per liter; for wet topsoil or loam, about 1.3–1.7 kg per liter; for lightweight engineered mixes, 0.5–0.7 kg per liter. Plants and roots typically add 5–20% to the media weight, and more for mature shrubs or small trees.
Examples:
- A 60 × 30 × 30 cm box = 54 L. With wet potting mix at 0.8 kg/L: about 43 kg of media. Add a 10 kg container and 5 kg of plants: about 58 kg.
- A 100 × 40 × 40 cm box = 160 L. Wet potting mix: about 128 kg; container: 20 kg; plants: 15 kg: about 163 kg. With wet topsoil at 1.5 kg/L, media alone is about 240 kg, total about 275 kg.
- A 120 × 60 × 50 cm box = 360 L. Wet potting mix: about 288 kg; container: 30 kg; plants: 25 kg: about 343 kg. Wet topsoil can push it above 500 kg.
So small balcony boxes may weigh 20–60 kg, medium urban planters 80–250 kg, and large rooftop or street planters 300–1,000+ kg. Always check the load rating of balconies, roofs, and decks; use lightweight media, good drainage, and distribute weight. Remember that wet weight is the design weight, not dry weight.