Mulching is one of gardening's highest-value tasks — it controls weeds, holds moisture and feeds the soil — yet most people guess the quantity. Matching your bed to the right depth turns a guess into a single order.
Depth is the real variable
Mulch volume is length × width × depth, and depth is the figure worth getting right. Too little is cosmetic, too much can damage plants. The sweet spot is 5–10 cm, which is also why the calculation so often lands somewhere between a handful of bags and a truckload.
Bags, bulk and the price per unit
Mulch arrives either in bags or by the truckload. Once you know your volume, convert everything to a price per cubic unit and the cheaper option is obvious — bulk usually wins for bigger jobs, while bags suit small beds and no truck access.
Reading the beds
Organic mulch breaks down and needs topping up each year — a budget item, not an annual surprise. Keep it off stems and trunks, and let the decomposing layer do its quiet work improving the soil underneath.
Frequently asked questions
Multiply the bed's length × width × depth. A standard 4×3 m bed at 7 cm needs about 0.84 m³ — roughly 14 sixty-litre bags.
5–10 cm (2–4 inches) is ideal. Less than 5 cm lets weeds through; more than 10 cm can suffocate plant roots and trap moisture against stems.
Both — a fresh layer in spring conserves moisture and suppresses weeds through summer, and a top-up in autumn insulates roots and feeds the soil as it breaks down.