How to Figure How Much Dirt to Put in a Flower Bed

Different types of flowering plants need varying amounts of soil.

Building a raised flower bed can be a simple task, or you can do some higher math to determine exactly how much topsoil, compost and other ingredients you include. Many small annual flowering plants, such as marigolds and petunias, need very little dirt. Because they can survive nicely in a pot with 4 to 6 inches of soil, you can surmise that they will thrive in a flower bed with an equal amount of soil. Larger plants need more soil, so base your calculations on the type of plant you want to grow.

Things You'll Need

• Measuring tape

Instructions

1. Measure the area where you plan to build a raised flower bed. Include the length, width and depth you want. A manageable size is about 8 feet long by 3 or 4 feet wide: the goal is to be able to reach into the center of the bed from either side without stepping on the soil that will make up your bed. The depth depends on the types of plants you plan to grow.

2. Multiply the length, width and depth numbers to determine the number of cubic feet. If you are planning a bed that is 8 feet long, 4 feet wide and 1 foot deep, you will arrive at 32 cubic feet of soil needed.

3. Calculate the number of cubic yards. Cubic yards are normally how you buy topsoil, compost and other materials. One cubic yard is comprised of 27 cubic feet, because there are 3 feet in each yard: 3 times 3 times 3 equals 27 cubic feet. For an 8 foot by 4 foot by 1 foot flower bed, divide 32 by 27, which comes to 1.185 cubic yards.

4. Estimate the amount of dirt or topsoil by looking at a small pickup truck's bed, which normally holds about 1 cubic yard of dirt or soil, mounded to a small peak in the center. If you want your flower bed to be the same approximate length, width and depth as your truck's bed, 1 cubic yard of dirt or soil will suffice. If you want flower beds that are half the depth of your truck's bed when filled with soil, 1 cubic yard will cover double the area of your truck's bed.

5. Build a rock or wooden border for your flower bed if you wish. Set it in place before you transfer your soil to the area where you want your flower bed.

Tips & Warnings

• For healthy, robust flowering plants, include organic compost with your topsoil at a ratio of about one part compost to every four parts of soil.

References

• American Topsoil: Frequently Asked Questions
• University of Missouri Extension: Raised Bed Gardening