Figuring out how much soil to buy for your new urban planter boxes is a common gardening hurdle. Buying too little means an extra trip to the store, while buying too much is a waste of money and space. Fortunately, calculating the correct amount is a simple math problem.
First, you need to determine the volume of your planter box. Grab a tape measure and find the length, width, and height (or depth) of the box in feet. If you measured in inches, simply divide each number by 12 to convert it to feet.
Next, use this formula: Length x Width x Height = Volume in Cubic Feet.
For example, a planter that is 4 feet long, 2 feet wide, and 1.5 feet high has a volume of 4 x 2 x 1.5 = 12 cubic feet.
Now, check the bags of potting soil at your local garden center. Soil is typically sold in bags measured in quarts or cubic feet. There are 25.75 dry quarts in one cubic foot. Therefore, if your planter box has a volume of 12 cubic feet, you will need to buy 12 cubic feet of soil. This might be one large bulk bag or several smaller bags that add up to that volume.
Remember not to fill your planter box completely to the top with soil; leave about an inch or two of space from the rim for watering. With this quick calculation, you can shop confidently, ensuring your plants have the perfect foundation to thrive.