Cómo funcionan las matemáticas

Mulch math is refreshingly simple — area times depth — but the depth number carries more science than people expect. Three inches is the sweet spot, and it's not arbitrary. Here's the full picture, from the 3-inch rule to the bag-vs.-bulk decision that saves real money.

The 3-inch rule: why depth matters

Two to four inches of mulch smothers weeds by blocking light, holds soil moisture through hot afternoons, and moderates soil temperature swings. Go thinner than 2 inches and weeds punch right through; go deeper than 4 and you smother the very roots you're trying to protect — and piling it against tree trunks ("volcano mulching") invites rot and rodents. Three inches is the standard because it does the whole job without the side effects.

Cubic yards: area × depth

Cubic yards = Area (sq ft) × Depth (ft) ÷ 27

A 10 × 20 bed is 200 square feet. At 3 inches (3 ÷ 12 = 0.25 ft): 200 × 0.25 = 50 cubic feet ÷ 27 = 1.85 cubic yards. That's the number bulk suppliers speak — they sell by the yard, dumped from a truck into your driveway.

Bags vs. bulk: the crossover point

A standard mulch bag holds 2 cubic feet, so bags needed = total cubic feet ÷ 2 — our 50 ft³ bed needs 25 bags. Here's a handy check straight off the bag label: "covers 8 sq ft at 3 inches deep" — because 2 ft³ ÷ 0.25 ft = 8 ft², the math always reconciles. Bags win for small beds (no delivery fee, no wheelbarrow marathon from the driveway pile); bulk wins past about 3–4 cubic yards, where the per-yard price crushes bag pricing.

Worked example: 10 × 20 flower bed, 3" deep

• Area: 10 × 20 = 200 sq ft
• Volume: 200 × 0.25 = 50 ft³ ÷ 27 = 1.85 cubic yards
• Bags: 50 ÷ 2 = 25 bags (or order 2 yards bulk)
• Waste factor: add 10% — mulch settles about an inch in the first month, and beds are never perfectly rectangular. Get 27–28 bags, or 2 full yards bulk.

Top-dress with an inch each spring to replace what decomposed — that's free slow-release fertilizer. Come for answers, leave with confidence.