How to Mulch A Garden
Learn how to mulch a garden step by step, with the tools, materials, and a free calculator to estimate exactly what you need. To calculate mulch, multiply the bed length by width to get the area, then by depth in feet, and divide by 27 for cubic yards. A 20×4 ft bed at 3 inches deep needs about 0.74 cubic yards (roughly 10 bags), costing about $22–$37 in bulk mulch.
Get exact numbers
Use the free Mulch Calculator to estimate your project.
Step-by-step
- 1
Measure the bed
Record length and width in feet.
- 2
Choose a depth
Convert inches to feet (3 in = 0.25 ft).
- 3
Find the volume
Multiply area × depth for cubic feet.
- 4
Convert to yards
Divide cubic feet by 27, or by 13.5 for 2 ft³ bags.
Pro tips
- Avoid: mulching too deep — More than 3–4 inches suffocates roots and holds excess moisture. Two to three inches is the sweet spot.
- Avoid: piling mulch against stems — "Mulch volcanoes" around trunks invite rot and pests. Keep mulch a few inches clear of stems and trunks.
- Avoid: ignoring existing mulch — If a bed already has mulch, you usually only need a 1-inch refresh — measure for the top-up, not the full depth.
- Avoid: buying bags for big beds — For large areas, bulk mulch by the cubic yard is far cheaper than bagged. Compare price per cubic foot.