There is no single maximum weight for an urban planter box on a wooden deck. The safe limit is set by the planter's construction, the wet weight of soil, water, plants, and container, and—most importantly—the deck's structural capacity, joist spacing, beam locations, and how the load is distributed. A common residential deck is designed for about 40–50 lb per square foot live load, but that is a distributed design value, not a guarantee for a concentrated planter. Wet soil weighs roughly 100–120 lb per cubic foot. For example, a 24 x 24 x 18 in planter holds about 6 cubic feet of soil, so wet soil alone can weigh 600–720 lb; with the container and plants, total weight may be 650–870 lb over 4 square feet, or 160–220 lb per square foot. That may be too much unless the planter sits near a bearing wall or beam and uses a load-spreading base. Smaller planters, lightweight soil mixes, and multiple distributed containers are safer. For any large planter, have a structural engineer or qualified deck contractor check the framing; do not rely on a simple planter-box weight rating.
What's the maximum weight an urban planter box can hold on a wooden deck?
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