How much mulch do you need? With calculation per m² and mulch type
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How much mulch do you need?
Mulching gives immediate benefits: moisture retention, weed control, temperature regulation, soil health. But many gardeners don't know how much they need. Too little = ineffective (thin layer). Too much = expensive and unnecessary.
This guide gives exact numbers per m² per mulch type.
Mulch formula
Cubic metres mulch = area (m²) × layer thickness (cm) ÷ 100
Example: 20 m² × 5 cm = 100 ÷ 100 = 1 cubic metre.
For 50 m² × 5 cm = 250 ÷ 100 = 2.5 cubic metres.
Mulch is sold per cubic metre (m³) or per bag (typically 40 litres = 0.04 m³).
How much mulch per layer depth?
5 cm layer (standard):
- 10 m² = 0.5 m³ = 12-13 bags (40 litres)
- 20 m² = 1 m³ = 25 bags
- 50 m² = 2.5 m³ = 62 bags
7 cm layer (better):
- 10 m² = 0.7 m³ = 17-18 bags
- 20 m² = 1.4 m³ = 35 bags
- 50 m² = 3.5 m³ = 88 bags
10 cm layer (very effective, but more):
- 10 m² = 1 m³ = 25 bags
- 20 m² = 2 m³ = 50 bags
- 50 m² = 5 m³ = 125 bags
Rule: 5-7 cm is standard. 10 cm for very dry area or serious weed problem.
Mulch types and characteristics
| Mulch type | Layer depth | Moisture retention | Weed control | Price | Durability |
|---|---|---|---|---|---|
| Bark chips | 5-7 cm | Good | Good | Low | 2-3 years |
| Wood chips | 5 cm | Very good | Very good | Moderate | 3-4 years |
| Composted bark | 7 cm | Good | Good | Moderate | 2 years |
| Coco husk (coco) | 3-5 cm | Very good | Good | High | 1-2 years |
| Leaf mould | 5 cm | Good | Moderate | Low | 1-2 years |
| Decorative bark (dark) | 5 cm | Good | Good | High | 2-3 years |
Best choice: Bark chips (budget) or Wood chips (performance).
Calculation per garden size
Small garden (20-30 m² border):
- 5 cm layer: 1-1.5 m³ (25-40 bags at 40L)
- Bark: £15-30
- Wood chips: £30-45
Medium garden (50 m² border):
- 5 cm layer: 2.5 m³ (60 bags)
- Bark: £30-60
- Wood chips: £75-110
Large garden (100+ m² border):
- 5 cm layer: 5 m³ (125 bags)
- Bark bulk: £60-110
- Wood chips bulk: £150-220
Laying and maintenance
Laying: Mulch on dry day. Remove weeds first, then spread mulch 5 cm thick (measure with ruler).
Maintenance: Each spring top up layer (2 cm replenish). Yearly ~30% settles/breaks down.
Caution: Don't lay against stem/trunk (diseases). 5-10 cm distance from woody plants.
Frequently asked questions
Can I use mulch for multiple years?
Bark/wood chips: 2-3 years. After breaks down and settles. No replacement = thinner layer = less effect. Annual top-up helps.
How much mulch front border vs back?
No formula difference. Back (full sun) can be thinner (less moisture-hold needed). Front (half shade): thicker helps more.
Which mulch around growing plants?
Bark good for perennials, ground covers. Wood chips better around shrubs/trees (slower breakdown).
Can mulch be home-made?
Yes. Grass clippings + leaf mould = free mulch, but less compact, more weed-seed. Not recommended for quality borders.
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