Mulch is a layer of material typically applied to the surface of soil, serving multiple functions in a landscape setting. Its primary roles include suppressing weed growth by blocking sunlight and retaining soil moisture by reducing evaporation. Mulch also helps moderate soil temperature, insulating plant roots from extreme heat and cold. Ordering the correct amount is crucial to maximizing these benefits while avoiding the expense and inconvenience of a shortage or excess material. This guide provides a simple, step-by-step method to accurately calculate the quantity of mulch needed.
Determining the Necessary Coverage Area
The process begins by accurately measuring the space to determine its total surface area. For rectangular planting beds, calculate the square footage by multiplying the length by the width. If the area is irregularly shaped, divide the space into smaller squares, rectangles, or triangles. Calculate the square footage of each segment and then add them together.
Once the total square footage is established, the next input needed for the calculation is the planned depth of the mulch layer. The recommended application depth for most organic mulches is between two and four inches for established beds. A layer thinner than two inches may not effectively block sunlight or prevent weed seeds from germinating. Conversely, applying more than four inches can be detrimental, potentially suffocating plant roots or promoting rot.
For general landscaping and effective weed control, a depth of three inches is often the ideal balance. The final volume calculation depends on both the horizontal coverage area and the vertical depth. Determining this precise depth beforehand ensures the correct amount is ordered for accurate budgeting.
The Calculation: Converting Square Footage to Cubic Yards
Mulch is sold in two volume measurements: cubic yards for bulk delivery or cubic feet for pre-packaged bags. A cubic yard is a volume equivalent to a cube three feet long, wide, and high. Understanding the relationship between these units is important, as one cubic yard equals 27 cubic feet.
To convert the measured area and chosen depth into the volume needed, a simple formula can be used that accommodates the different units involved. Multiply the total square footage by the desired depth in inches, and then divide that result by 324 to determine the volume in cubic yards. The number 324 is derived by multiplying 12 inches (in a foot) by 27 cubic feet (in a cubic yard). This combined constant simplifies the unit conversions.
For example, imagine a garden bed measuring 20 feet long by 15 feet wide, resulting in a total surface area of 300 square feet. If the application depth is set at 3 inches, the calculation is 300 multiplied by 3, which equals 900. Dividing 900 by the constant 324 yields a total volume requirement of 2.78 cubic yards.
Practical Considerations for Ordering and Delivery
The calculated volume represents the theoretical minimum amount of mulch required for the project. When ordering bulk material, the volume must be rounded up to the nearest whole or half-yard increment, typically resulting in an order of 3 cubic yards. Bulk ordering usually involves delivery, which may have a minimum order size or an associated fee, so it is wise to confirm these logistical details with the supplier. It is also beneficial to remember that a single cubic yard of mulch creates a substantial pile.
Alternatively, for smaller projects, mulch may be purchased in bags, which commonly come in 1.5, 2.0, or 3.0 cubic foot sizes. To determine the number of bags needed, the total volume required must first be converted from cubic yards into cubic feet by multiplying the cubic yard figure by 27. Using the previous example of 2.78 cubic yards, this equates to 75.06 cubic feet of mulch needed.
If using bags that contain 2.0 cubic feet of mulch, dividing the total cubic feet needed by the bag size (75.06 divided by 2.0) indicates a requirement of 37.53 bags. Since bags are not sold in halves, this quantity must be rounded up to 38 bags. It is a sound practice to include an additional 5 to 10 percent in the order. This accounts for factors like uneven application, settling, or minor waste during spreading.