Got Mulch? Here’s How Much You Need.

Adding a layer of mulch to your planting beds is the best thing you can do for your garden this year. Sure, you’ll get hot and weary long before you’re done with the chore. But mulch offers a huge payoff: beautiful beds, fewer weeds, and healthier plants. Here’s everything you need to know before pulling out all of those gardening tools and rolling up those sleeves (and putting on your garden shoes and gardening gloves!) and getting started.

From “How much mulch do I need?” to “What is mulch, anyway?”, we broke down everything you need to know about this soil covering. So, before you roll up your sleeves and get going with your gardening, consult our mulch calculator and other essential tips.

What Is Mulch and What Does It Do?

Mulch—material made up of bark, leaves, or compost and used to cover soil—isn’t only about making your yard look neat and attractive. “One of its big benefits is that it helps conserve moisture in the soil by acting as a barrier to evaporation,” says John Esslinger, horticulture educator at Penn State Extension. “It also reduces the number of weeds and improves organic matter in soil, making your beds more productive over time.”

So, where should you mulch? Everywhere! Beds of annual or perennial plants, flowering shrubs, veggie gardens, and even containers benefit from mulch, which keeps the roots of new plantings moist as they’re getting established. And mulch protects tree trunks from string trimmers or mowers; just don’t mound it up directly against the trunk into a “mulch volcano.” That invites moisture and decay. “The organisms that break down mulch start working on the bark, too,” says Esslinger.

How Much Mulch Do I Need?

A 2″ depth of organic mulch is ideal to retain moisture and keep down weeds, says Esslinger. But don’t go overboard: This is one time when more is not necessarily better. Plant roots need air to survive, and too deep a layer can suffocate roots and cause water to shed off the top of mulch instead of filtering through and soaking into the soil below.

The maximum depth you should apply depends on the type: Finely textured mulch, like shredded hardwood, shouldn’t be more than 3″ deep. Coarse textures, such as pine bark nuggets, allow more air movement so you can go up to 4″ deep.

First, figure out the square footage of your bed. Multiply width by length for square or rectangular beds—or for round beds, multiply the radius (distance from the middle to the edge of the bed) by itself, and then multiple that total by 3.14.

Keep in mind that mulch is sold by the cubic yard. One cubic yard of the material covers a 324-square-foot area an inch deep. So, to determine your total, multiply your square footage by the depth in inches desired, then divide by 324.

Here’s your formula: Square footage x desired depth / 324 = cubic yards needed.

Here is another way:

Work out the size of the garden bed you want to cover and multiply this by the depth you need.

Say your garden bed is about 3metres wide by 3metres long, then you multiply 3×3 and know you have 9 square metres to cover.

Next comes the depth. If you want mulch that is, say, 10cm (or 0.1metres) deep then you multiply the size of the garden bed by 0.1m.

For your 3×3 bed, that means 3x3x0.1 = 0.9metres, which is just under a cubic meter.

Another way to picture a square meter is to remember it is about 10 good-sized wheelbarrows full.