How deep should bark mulch be?

Bark mulch should be 50-75mm (2-3 inches) deep for effective weed suppression. A 50mm layer is the minimum for reasonable coverage, while 75mm provides the best results. Going deeper than 100mm is wasteful and can prevent water from reaching plant roots. For play areas, safety bark needs to be at least 300mm deep.

How much does bark mulch weigh?

Bark mulch weight varies by type: fine bark weighs approximately 350 kg per cubic metre, medium bark chips about 300 kg/m³, and ornamental decorative bark around 280 kg/m³. A standard 1m³ bulk bag of medium bark typically weighs 280-320 kg. Weight also varies with moisture content — wet bark is significantly heavier.

What type of bark mulch is best for flower beds?

Medium bark chips (15-35mm) are the most popular choice for UK flower beds and borders. They break down slowly, suppress weeds effectively, and improve soil structure as they decompose. Fine bark (under 15mm) is better for a neat, uniform look but decomposes faster. Ornamental bark (pine bark nuggets) looks decorative but is lighter and can float away in heavy rain.

How often should I top up bark mulch?

Top up bark mulch once a year, usually in spring. Fine bark decomposes in 1-2 years, medium bark in 2-3 years, and ornamental bark in 3-4 years. You typically need to add 25-50mm each year to maintain the recommended depth. The decomposing bark improves your soil, so it is a beneficial process.

Should I put weed membrane under bark mulch?

Weed membrane under bark mulch is recommended for paths and areas without plants. For flower beds, it is not always necessary — 75mm of bark alone provides good weed suppression and allows the decomposing bark to feed the soil. If you do use membrane, choose a woven landscape fabric rather than plastic sheeting. Use our Weed Membrane Calculator to work out the quantity needed.

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Bark Mulch Calculator — How Many Bags of Bark Do I Need?

Calculate bark mulch volume in bulk bags and litres for flower beds, borders and decorative areas. UK weight estimates included.

Bed Length

Length of each bed

Bed Width

Width of each bed

Number of Beds

How many beds of this size

Mulch Depth

50-75mm recommended for weed suppression

Mulch Type

Medium bark chips (~300 kg/m³)

Bulk Bag Size

Choose 0.5 m³ or 1.0 m³ bags

Price Per Bulk Bag (optional)

Enter your supplier price for a cost estimate

How We Calculate This

Our bark mulch calculator multiplies your bed dimensions by the required depth to get the total volume in cubic metres, then converts to litres, weight and bulk bags.

The formula

Total area = Bed length × Bed width × Number of beds

Volume (m³) = Total area (m²) × Depth (m)

Litres = Volume (m³) × 1,000

Weight (kg) = Volume (m³) × Density (kg/m³)

Bark mulch densities

Fine bark: ~350 kg/m³
Medium bark chips: ~300 kg/m³
Ornamental bark: ~280 kg/m³

Recommended depths

Weed suppression: 50-75mm
Decorative beds: 50mm minimum
Play area safety bark: 300mm minimum

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.