How to Mulch and Edge a Bed

Finishing a bed is a small job with three orders in it, and all three are commonly wrong in the same direction: too much soil, not enough mulch, and edging for a perimeter that does not need edging.

Mulch: depth is the decision

The Mulch Calculator gives cubic yards and bags from the bed size and how deep you want to go — and that depth is the whole decision, not a detail.

Too thin and it does not do its job: mulch suppresses weeds and holds moisture by blocking light and slowing evaporation, and a scattering does neither. Too thick against stems and trunks holds moisture where you least want it.

Pick the depth deliberately, then let the calculator do the arithmetic. Estimating "a few bags" for a bed is how people end up with a thin, patchy layer that needs redoing in six weeks.

Topsoil: order for after it settles

The Topsoil Calculator gives cubic yards and tons, with the allowance that matters: topsoil delivered loose loses roughly a fifth of its depth once it beds in.

So the pile that looks generous on delivery day is the right amount, and the pile that looks right on delivery day is short. Order to the settled depth you want to end up with, not the depth you want to see when it arrives.

It reports tons as well as yards for the same reason the gravel tool does — suppliers quote one or the other, and they are not interchangeable.

Edging: not all the way round

The Garden Edging Calculator gives linear feet, pieces and stakes — and it handles the thing people forget: a bed against a wall does not need edging all the way round.

This sounds obvious written down and is missed constantly, because the natural way to estimate a border is to measure the bed's perimeter. A bed along a fence, a house wall, a path or a driveway only needs edging where it meets something that needs holding back — usually lawn.

Measure the edge that actually needs edging. On a bed against a wall that can be half the perimeter, and edging is sold by the piece.

Doing it in one go

If you are topping up soil and mulching in the same session, order both together and put the soil down first. Mulch belongs on top as a covering layer, not mixed in — and buying them on separate trips is how the mulch depth ends up decided by what was left in the car.

The short version

1. Choose the mulch depth on purpose. It is the whole calculation.
2. Order topsoil about a fifth over the finished depth — it settles.
3. Check whether topsoil is quoted in yards or tons.
4. Only edge the edge that needs it. A bed against a wall is not a full perimeter.

Each tool has a printable with its own assumptions, which is worth taking to the garden centre where everything is priced by the bag.