How to know the amount of mulch you need

By Tim Johnson
Chicago Botanic Garden
Posted11/28/2021 7:00 AM

I typically do not mulch established perennial borders but leave the perennials up for the winter and let some fall leaves blow in. Perennials that start to look bad (such as hosta, which will eventually collapse after being frozen) can be cut back to tidy things up. This has more of a natural (not manicured) look, which I prefer.

Cutting back your perennials and top dressing the bed with a light layer of mulch will result in a neat appearance. Some books recommend waiting until the ground freezes to apply mulch, but I do not wait.


To calculate the amount of mulch needed for a bed, first convert all measurements to feet. One foot equals 12 inches. To figure the square feet of a bed, multiply the length of the bed times the width. To convert the depth of mulch to feet, divide the inches of mulch you intend to apply by 12. If your mulch is to be 1 inch deep, take 1 inch divided by 12 inches. This gives you a .08-foot depth of mulch.

Use the following formula to calculate the amount of mulch needed for 1 inch of depth over a bed that is 18 feet wide by 37 feet long. Eighteen feet times 37 feet equals 666 square feet of bed space. One inch divided by 12 inches equals .08 feet. Multiply 666 square feet times .08 feet of mulch to equal 53 cubic feet of mulch. One cubic yard of mulch is 27 cubic feet, so divide 53 cubic feet by 27. Your order should be 2 cubic yards of mulch.

Bagged mulch comes in different sizes. Typically, 2- or 3-cubic-foot bags work well for small beds. For the bed above, you would divide the 53 cubic feet of mulch required by the amount of mulch in the bag. Dividing 53 cubic feet by 3 cubic feet per bag equals 18 bags and 53 cubic feet divided by 2 cubic feet per bag equals 27 bags of mulch. For this bed, it will be more economical to buy the mulch in bulk.

• It is a good idea to sharpen and clean garden tools when putting them away for the season. Sharpen spades with an electric hand grinder and put the bevel on the inside edge of the spades.

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It is important to wear ear and eye protection for this task as it is noisy, and sparks will fly as the grinder works. Move the grinder steadily back and forth to create the sharp edge and avoid burning the metal.

Well-maintained tools make gardening much easier. Use pegboard on your garage walls to hang and organize tools. If your garage is unheated, it is best to store liquids indoors.

• Have your snowblower serviced before the first measurable snowfall when repair shops may get backed up with repair and maintenance work.

• Tim Johnson is director of horticulture at Chicago Botanic Garden,

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