Mulch Calculator — How Much Bark Mulch You Need

To suppress weeds effectively, the bark layer should be 5–7 cm thick. A thinner layer lets light through and does not block weed growth, while too thick a layer limits air access to roots. Laying landscape fabric under the bark improves the effect.

For 1 m² at a 5 cm layer you need 0.05 m³ (50 litres), at 7 cm — 0.07 m³, and at 10 cm — 0.10 m³. Volume equals area in m² times thickness in metres (cm/100). The calculator does this automatically.

Decorative bark (coarse) looks neat and breaks down slowly — good for ornamental beds. Functional bark (finer, composted) retains moisture better and enriches the soil faster. The choice depends on whether you prioritise looks or soil protection.

Mulch is usually topped up every 1–2 years as it settles and decomposes. Coarse pine bark can last up to 3 years. Adding a thin layer each season keeps it at 5–7 cm and maintains protection against weeds and water loss.

Pine bark is durable and attractive and breaks down slowly — good for decoration and paths. Composted bark has fewer resins, releases nutrients faster and suits demanding plants and vegetable beds better.

Fresh pine bark slightly acidifies the soil, which benefits acid-loving plants such as rhododendrons, azaleas, blueberries and heathers. For plants preferring neutral soil, use seasoned bark. The acidifying effect is moderate and mostly affects the top layer.

Yes, decomposing fresh bark temporarily uses soil nitrogen. That is why bark is a top layer, not mixed into the soil, and demanding plants benefit from extra nitrogen fertiliser. Composted bark locks up less nitrogen than fresh bark.

A 50 L bag covers 1 m² at a 5 cm layer (0.05 m³). For a 20 m² bed at 5 cm you need 1 m³ of bark, i.e. 20 bags of 50 L. The calculator converts volume into 50 L bags and rounds up so you have a reserve.

You can spread it on weed-free soil, but laying water-permeable landscape fabric first improves the result. The fabric blocks weeds and stops bark mixing with the soil. Loosen and water the soil beforehand.

No. It calculates the volume of a freshly laid layer of the given thickness. Over time bark settles and decomposes. Treat the result as indicative — add about 5–10% extra when buying for uneven ground and losses.