Information Possibly Outdated
The information presented on this page was originally released on March 27, 1997. It may not be outdated, but please search our site for more current information. If you plan to quote or reference this information in a publication, please check with the Extension specialist or author before proceeding.
Calculate Mulch, Soil Needs For Plant Beds
By Norman Winter
Central Mississippi Research & Extension Center
Mulching is one of the most important things we can do for our shrubs, trees and flower beds, and planting time is a good chance to show you care.
Buying mulch or landscape soil mix can be a challenge when you don't know how much you need. People often try to look like they know what they are doing even when they don't.
Even if you are mathematically challenged, here is an easy formula to figure how much mulch or landscape soil mix you will need for your bed. First, it is critical to know there are 27 cubic feet in a cubic yard. One cubic yard will cover a 324 square foot area with one inch of soil or mulch.
Figure out the square footage of your bed, that's width times the length for square- or rectangular-shaped beds. My 11-year-old daughter helped me remember how to figure out the area of a triangle. It is the base times height, divided by two.
Circular beds are popular in the South. To find out the square feet, go to the middle of the circle and measure to the outside. This is your radius. Multiply this number by itself.
For example, if the distance was six, multiply by six to get 36. Then multiply 36 by 3.14 (which is pi, remember pi?). This will determine your area in square feet. Won't you impress friends when you tell them you used pi to figure out how much mulch to buy?
Taking the time to calculate the amount can be worth the effort. Although a little extra mulch around the house is kind of like having money in the bank, too much can be overwhelming.
Multiply your square footage times your depth of inches and divide by 324 square feet, which is one cubic yard, one inch deep. This will tell you how many cubic yards you will need.
If you have 100 square feet and want to add three inches to the depth, multiply 100 by three, and then divide by 324 to convert to cubic yards. This equals .92 cubic yards that you need, so you can buy nine of the three-cubic-feet bags. Since 27 cubic feet equal one cubic yard, you will have just a little bit left over.
Mulch prevents moisture loss, and come July and August, those newly planted trees and shrubs will need all available moisture. It keeps soil from being compacted. Compacted soil prevents moisture from reaching those roots and stifles the available oxygen. Mulch keeps the soil cool in the summer and actually stabilizes it in the winter too.
One much overlooked benefit is that mulch helps deter weeds. Weeds that practically need a stick of dynamite to be removed in tight soil can usually be easily plucked in a well mulched bed. Pay attention to what landscapes catch your eye and which ones look most professional. Landscapes with plantings on raised beds with an application of fresh mulch usually will be the ones that receive those appreciative stares.