How Much Mulch Do I Need?

The 10-second answer: the mulch formula

Here it is, the formula I've scribbled on a thousand invoices: square feet of bed × depth in inches ÷ 324 = cubic yards of mulch. That's it. A 300 square-foot bed at 3 inches deep needs 300 × 3 ÷ 324 ≈ 2.8 cubic yards. Round up to 3 and you're done.

Measuring an odd-shaped bed? Break it into rough rectangles and circles, add them up, and don't agonize — mulch forgives estimates within 10%. Or skip the math entirely: Backyard Buddy's free Material Calculator converts your measurements into exact yards (and bags) in seconds.

How deep should mulch be?

Two to three inches. Less than 2 inches and weeds laugh at you; more than 4 and you suffocate roots, invite fungus, and waste money. Around trees and shrubs, keep it to 2–3 inches and pull it back from the trunk — you want a donut, never a volcano.

Refreshing existing beds? You usually only need a 1-inch top-up each spring. Rake the old layer first to break the crust so water gets through.

Bulk or bags? The break-even math

One cubic yard equals 13.5 of those 2-cubic-foot bags. Bagged mulch usually runs 2–3× the price of bulk per yard. My rule from three decades of ordering: under 10 bags, buy bags — easy to haul, easy to store. Over 10 bags (about ¾ of a yard), order bulk from a local landscape supply yard and have it delivered.

Bulk mulch is also usually fresher and darker than what's been cooking in plastic bags in a parking lot since March. Ask your local supplier what they have in double-shredded — that's the workhorse.

Which mulch should you buy?

Mulch isn't just mulch. Some feed your soil as they break down, some hold color longer, some are better on slopes. The table below is the honest cheat-sheet I give clients — what I actually recommend, and what I quietly steer people away from.

When to mulch (and how often)

Mulch after the soil warms in late spring — mulching cold, wet soil in early April keeps it cold and wet. In most zones, mid-May is the sweet spot. A lighter fall top-up before the ground freezes helps perennials overwinter.

Expect to refresh 1 inch every year for natural mulches (that's the good stuff feeding your soil as it decomposes). Dyed mulches hold color longer but feed the soil less — nothing is free in gardening.

Linda's mulch cheat-sheet