Mulch Calculator — Bags & Coverage

Mulch volume is calculated as area × depth. The RHS recommends applying organic mulch (bark, wood chip, garden compost) to a depth of 50–75 mm (5–7.5 cm). This depth suppresses weeds, retains moisture and insulates roots without smothering the soil. For gravel mulch, 25–40 mm is usually sufficient.

This calculator shows volume in cubic metres, litres and the number of bags needed. Standard bags are 50–80 litres; bulk bags hold approximately 0.5–1.0 m³. Bark mulch weighs roughly 300–400 kg per m³ loose; composted material is heavier at 500–700 kg per m³.

Enter the bed area and desired depth. The calculator shows total volume, bags or bulk bags needed and estimated cost. Apply mulch in late spring after the soil has warmed, or in autumn. Keep mulch 5–10 cm away from plant stems and tree trunks to prevent rot.

How much mulch do you need? Volume = area × depth. Standard depth: 50-75mm (2-3 inches) for established borders. Heavier 100mm for weed suppression. Sample 20 m² border × 75mm = 1.5 m³ mulch. Bulk bag (UK): 0.7-0.9 m³ = 1 bag covers ~12 m² at 75mm. Loose load (truck delivery): 3-15 m³, cheaper per m³ but needs access. Bag (small retail): 50-70L = 0.05-0.07 m³ = covers 0.7-1 m² at 75mm.

UK mulch types and prices 2026. Bark mulch (decorative): £45-£90/bulk bag. Wood chip: £30-£60/bulk bag (cheaper, more rustic). Composted bark: £55-£100/bulk bag (premium, soil-improving). Garden compost (DIY or municipal): free if you compost; £30-£50/bulk bag commercial. Coco husk: £40-£90/bag (eco-credentials, lightweight). Stone/slate chippings: £60-£140/bulk bag (long-lasting, no enrichment). Black plastic mulch (commercial): cheap but eco-poor.

Benefits of mulching. Suppresses weeds: 70-90% reduction with 75mm+ depth. Retains soil moisture: 30-50% less watering needed in summer. Insulates roots from extreme temperatures. Slowly breaks down adding organic matter (bark, compost). Earthworm-friendly habitat increases soil biology. Reduces soil erosion on slopes. Prevents soil splash on plants (reduces disease). Looks tidy — neat borders. UK climate: spring mulching ideal — moist soil, suppresses weeds before they germinate.

When and how to apply. Best time: mid-spring (March-May) when soil moist but warming. Avoid: hot dry summer days (locks in heat, traps dryness); frozen ground; mid-summer when weeds already established. Application: weed area first; water soil if dry; apply 75-100mm depth around plants but NOT touching stems (rot risk); top up annually (decomposes 20-50%/year for organic mulches). Don't pile against tree trunks ('mulch volcano') — bark rots, attracts pests.

Specialist mulches. Ericaceous mulch (composted bracken or pine needles): for acid-loving plants (rhododendrons, azaleas, blueberries). Strawberry straw: traditional UK ground cover for fruit — protects berries from soil. Living mulches (clover, vetch): green manure crops sowed between rows, dug in at end of season. Glass nuggets: long-lasting decorative, no environmental benefit. Rubber mulch: cheap, but synthetic — environmental concerns, doesn't improve soil. Choose based on: aesthetic, soil benefit goals, cost, longevity.