URBAN PLANTER BOXES

To fill a 24-inch urban planter box, first confirm whether 24 inches is the length, width, or diameter. For the most common square 24-inch planter, use the interior dimensions and multiply length × width × depth. The formula is: volume in cubic feet = (length in inches × width in inches × depth in inches) ÷ 1,728. For a 24 × 24-inch box, this simplifies to depth ÷ 3 cubic feet. That means a 24 × 24-inch planter needs about 4 cubic feet of soil at 12 inches deep, 6 cubic feet at 18 inches deep, and 8 cubic feet at 24 inches deep. If the box is 24 inches long but not 24 inches wide, use: (24 × width × depth) ÷ 1,728. For a round 24-inch-diameter planter, the volume is about 3.1 cubic feet at 12 inches deep, 4.7 cubic feet at 18 inches deep, and 6.3 cubic feet at 24 inches deep. If your planter has a false bottom or water reservoir, measure only the actual soil depth. Buy 5–10% extra soil to allow for settling, and leave 1–2 inches of space below the rim. With 2-cubic-foot bags, plan on about 2 bags for 4 cubic feet, 3 bags for 6 cubic feet, and 4 bags for 8 cubic feet. With 1.5-cubic-foot bags, plan on about 3, 4, and 6 bags respectively. Use a lightweight planter mix rather than heavy garden soil, and make sure drainage is adequate.