That's an excellent question! Figuring out the right amount of soil is key to a successful container garden. For our average-sized urban planter box, which is typically around 24 inches long, 12 inches wide, and 12 inches deep, you can easily calculate the soil volume you'll need.
Here’s the simple math: Multiply the Length x Width x Depth (using the same unit, preferably feet). For our example: 2 ft (L) x 1 ft (W) x 1 ft (D) = 2 cubic feet.
Most bagged potting soil is sold by the cubic foot or by the quart. Therefore, to fill this example planter box, you would need approximately 2 cubic feet of soil. This is equivalent to about 60 dry quarts. We always recommend getting a little extra—around 10-15% more—to account for settling as the soil compacts after the first watering.
Remember, it's crucial to use a high-quality potting mix, not garden soil, for proper drainage and aeration in your planter box. Simply fill the box to about 1-2 inches below the rim to prevent water from overflowing. Happy planting