Introduction

Behind every bag of Multipurpose Compost (MPC) lies one simple truth: each manufacturer usually builds around one dominant base material. That base defines texture, moisture behaviour, and environmental footprint — with smaller additives then used to adjust nutrients or pH.

The five main bases used in UK retail MPC are: Peat, Coir (coconut fibre), Wood Fibre, PAS100 green-waste compost, and Digestate fibre.

Every base offers similar overall aims — a clean, stable medium that balances air, water, and structure — but achieves them in different ways.

What All Bases Aim to Deliver

Regardless of source, a good MPC base should provide: structure, porosity, WHC (Water-Holding Capacity), aeration, nutrient moderation, and low contamination. Those are the design targets; how well each product meets them depends entirely on the chosen base material.

Peat

Peat remains the traditional reference standard for consistency and workability. It’s light, fine, and naturally sterile, giving predictable drainage and nutrient control. Its drawbacks are well known: extraction releases long-stored carbon and destroys bog habitats.

Coir (Coconut Fibre)

Coir comes from the husk of coconuts and has become the global front-runner for peat-free bases. It holds water well, has a soft texture, and decomposes slowly. Although shipped from Asia, life-cycle analyses show its carbon footprint is often lower than expected when transport and production energy are compared with peat extraction.

Wood Fibre

Wood fibre is made by thermally or mechanically defibrating softwood chips. It creates an open, airy structure that resists compaction and improves drainage.

PAS100 Green-Waste Compost

Composted green waste certified to PAS100 adds stable organic matter and natural microbial life. Some smaller MPC producers use it as the dominant base — especially those marketing local or circular-economy products.

For a full breakdown of how “compost” is defined on this site, see [[What Is Compost – The Three-Phase Reality]].

Wood-Rich Composts: The Hidden Variable

Even certified composts vary dramatically in texture. PAS100 sets limits on contaminants and stability but does not guarantee fineness or full humification. Typical grades are ≤25 mm or ≤15 mm, meaning many still contain 25–50% woody bulking material from the composting process.

• act like slow-release carbon (good for structure, poor for feeding plants),
• tie up nitrogen temporarily during further decay,
• and can reduce water-holding if the chip fraction is high.

Digestate Fibre

A newer entrant is digestate — the fibrous residue from anaerobic digestion of food or farm waste. After composting or drying, it forms a lightweight, nutrient-rich substrate.

Typical Base Choices by Brand

Dominant Base	Example Retail Brands	Notes
Peat	Legacy or professional lines (limited availability)	Being phased out of retail.
Coir	SylvaGrow, RocketGro, Carbon Gold	High moisture retention; premium feel.
Wood Fibre	Westland New Horizon, Levington Peat Free, Melcourt	Light, airy, UK-sourced materials.
PAS100 Compost	Dalefoot, some local authority blends	Circular, biologically active; watch pH.
Digestate Fibre	Blooming Amazing, Natural Grower, niche farm-based brands	Nutrient-rich, sustainable but variable.

(Brand names used for illustration only; actual recipes change frequently.)

How This Supports Our Review System

Understanding each base material allows us to review Multipurpose Composts on what they are made from, not just how they feel out of the bag. When a product performs well or poorly, we can trace the cause — whether it’s Coir’s fine water retention, Wood Fibre’s aeration, or PAS100’s woody fraction. This approach means our independent reviews are both repeatable and transparent, rooted in measurable properties rather than vague “looks and feels” opinions.

Summary: Choosing by Base

• Coir: Consistent, renewable, and versatile; good LCA when processed responsibly.
• PAS100 compost: Active and circular; watch pH and woody content.

When you know the base, you know how the compost will behave — moisture, drainage, feeding needs, and environmental footprint all follow from that single choice.