How much mulch do I need

Measure the beds as rectangles

Beds are rarely rectangles, but mulch is forgiving. Measure the longest length and the widest width of each bed and multiply; a curved bed measured that way comes out a little generous, which covers the corners you missed. A bed that wraps around the house is two rectangles. If several beds are about the same size, count them in the areas field; if not, add up the square footage with the square footage calculator, which takes three rectangles and a circle, and type it in as one bed.

Subtract nothing for shrubs unless they are large. A tree ring is a circle: for a ring 6 ft across, use a 6 × 6 ft square and accept the small overage.

How deep

New mulch on bare soil goes on 2–3 in deep. That is enough to shade out weed seed and slow evaporation without smothering roots; at 4 in and more it starts to keep air and water out of the soil. If there is already mulch that has faded but not broken down, rake it, break the crust and add 1–2 in on top. Fine mulches such as shredded bark pack tighter and can go 2 in; coarse nuggets and wood chips settle less and want the full 3 in. Keep it 2–3 in away from the stems of shrubs and 6 in from tree trunks. Mulch piled against bark holds water against it and invites rot and rodents.

Measuring and buying

1. Measure each bed’s length and width at its longest and widest points.
2. Type the first bed and set the areas field to how many beds are that size. Run the sheet again for beds of a different size and add the cubic yards.
3. Set the depth: 3 in for a new layer, 1–2 in to top up.
4. Compare the bulk and bagged totals at the prices on the sheet, then edit them to what your garden center or yard quotes, including delivery.
5. Order bulk by the cubic yard, rounded up; the sheet’s 5 % allowance covers spillage and the pile settling in the truck.
6. Have it dropped on a tarp on the driveway, not on the lawn, and spread it within a few days.

Bags or a bulk load

A cubic yard is 27 cu ft, so it is 13.5 bags of 2 cu ft or 9 bags of 3 cu ft. At 3 in deep a cubic yard covers about 100 sq ft (108 sq ft by the arithmetic, a little less once it settles). Bags make sense for a bed or two or if you have no way to take a delivery; you can buy them a few at a time and stack the spares. Above two or three yards, bulk is usually cheaper even with the delivery fee, and it comes without the plastic.

Mulch is light. Bark and wood mulch weigh about 0.4 tons per cubic yard dry, so a level pickup load of about 2 cu yd is within a half-ton truck’s payload unless it has been rained on. Bulk loads are sold loose and settle in the truck, which is why yards heap the bed.

Common mistakes

• Volcano mulching: mounding mulch up the trunk of a tree. Pull it back to a flat ring with bare soil at the trunk.
• Going too deep. Over 4 in the soil under it stays soggy and roots grow up into the mulch.
• Measuring the narrow part of the bed. Measure the widest point; a little extra is cheap and a second trip isn’t.
• Choosing by color rather than by job. Dyed mulch and natural bark spread the same and last about as long; the dye is a preference, not a rule. Fine mulch for beds you replant, coarse chips for paths and under trees.