Figuring out how much soil to buy for your planter box is a common question for urban gardeners. Buying too little means an extra trip to the store, while buying too much is wasteful. The key is to calculate the volume of your planter box. Here’s a simple guide.
First, measure your planter box in feet. For a standard rectangular box, measure the interior Length, Width, and Depth (height). Multiply these three numbers together:
Length (ft) x Width (ft) x Depth (ft) = Volume in cubic feet.
For example, a box that is 4 feet long, 2 feet wide, and 1.5 feet deep has a volume of 4 x 2 x 1.5 = 12 cubic feet.
For a cylindrical planter, measure the interior Radius (half the diameter) and Depth. Use the formula:
3.14 x (Radius x Radius) x Depth = Volume in cubic feet.
A pot with a 1.5-foot radius and a 2-foot depth has a volume of 3.14 x (1.5 x 1.5) x 2 ≈ 14.1 cubic feet.
Most bagged soil is sold in cubic feet (e.g., 1 cu ft, 1.5 cu ft, 2 cu ft bags). Simply match your calculated volume to the bag sizes. It’s wise to buy a little extra—about 5-10%—to account for settling as the soil compacts after watering.
Remember, you don’t need to fill the box entirely with soil. Leave about 1-2 inches from the top for mulch and watering. Also, ensure your planter has adequate drainage holes to keep your plants healthy. With this quick calculation, you can purchase the perfect amount of soil for your urban garden project.