Mulch & Bark Calculator
Calculate how much mulch, bark or wood chip you may need — in m³, litres, bulk bags and small bags. Includes settling allowance and 2026 UK pricing.
Woodland mulch: ~400 kg/m³. Fine texture, breaks down in 12–18 months, improves soil structure.
Area = π × (diameter ÷ 2)²
Use this if you already know your total area from a plan, survey or previous calculation.
75mm is the recommended depth for effective weed suppression and moisture retention.
Mulch and bark settle and compress over the first few weeks. 10% is standard.
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Application Guide
How to Apply Mulch
The Donut Method — Avoid Volcano Mulching
The most common mulching mistake is piling material directly against tree trunks and shrub stems — known as volcano mulching. This traps moisture against the bark, causing rot, fungal disease and rodent damage over time.
Always use the Donut Method: apply mulch in a wide ring but leave a 5cm gap around the base of each plant. You get all the moisture-retention and weed-suppression benefits without risking the plant.
Choosing the Right Depth
25mm (top-up): refreshes existing mulch at the start of each season. Restores appearance and tops up the weed-suppression layer.
50mm: basic moisture retention and light weed suppression. Suitable for established beds with dense planting.
75mm (recommended): the standard depth for effective weed suppression and thermal insulation. Reduces watering frequency by up to 38% in dry summers.
100mm: deep protection for new borders, particularly on slopes or in areas with persistent weed pressure.
Woodland Mulch vs Ornamental Bark
Woodland mulch is finer, breaks down in 12–18 months and improves soil structure as it decomposes. It is better for vegetable beds and borders where you want to build soil fertility over time. Density: ~400 kg/m³.
Ornamental bark has larger chips that take 2–3 years to break down, making it more cost-effective for long-term weed suppression in established borders and paths. Lighter at ~350 kg/m³.
FAQ
Common Questions
75mm is the recommended depth for effective weed suppression and moisture retention. A 50mm layer provides basic protection. Top-up dressings of 25mm refresh existing mulch each season. Depths over 100mm can exclude too much air and water from the soil.
A standard 500L bulk bag covers approximately 6.5 m² at 75mm depth, or 10 m² at 50mm depth.
The Donut Method means applying mulch in a wide ring around a tree or shrub while leaving a 5cm gap around the trunk or stem. Mulch piled directly against bark traps moisture and causes rot — the gap allows the root flare to breathe while still providing all the weed-suppression and moisture benefits.
Woodland mulch is finer and breaks down faster (12–18 months), adding nutrients to the soil. Ornamental bark has larger chips that last 2–3 years, giving better long-term weed suppression and a tidier appearance. For new borders use woodland mulch; for established decorative borders use ornamental bark.
A 75mm mulch layer acts as a thermal insulator, shading the soil surface and dramatically reducing evaporation. In dry UK summers, a proper mulch layer can reduce watering frequency by up to 38% by keeping soil temperatures stable and retaining moisture below the surface.