If you’ve ever opened a bag of compost and spotted a bit of plastic, glass, or grit, you’re not alone. A decade ago this was common — especially in peat-free composts made from recycled green waste.
Today, however, the picture has changed dramatically. Most modern Multipurpose Composts (MPCs) contain no green waste at all. Instead, they use clean, engineered base materials such as wood fibre, bark fines, coir, or digestate blends, which are far less likely to carry contamination.
Where contamination risk still comes from
- Legacy PAS100 composts (used in some bulk soil improvers or low-cost mixes)
- Cross-contamination during handling or storage at depots
- Incomplete screening in digestate-derived materials
- Transport and packaging residues (fragments of plastic bale wrap or pallet film)
Typical base materials today
| Core Base Type | Typical Source | Contamination Risk | Notes |
|---|---|---|---|
| Wood fibre / bark fines | Virgin forestry residues | Very low | Mechanically processed, not recycled waste. Most mainstream MPCs now use this as their main base. |
| Coir (coconut fibre) | Processed coconut husks from Asia | Very low | Clean, renewable, and well-graded for horticulture. |
| Digestate (fibre fraction) | Anaerobic digestion of food or crops | Low–moderate | Quality depends on screening and pre-sorting. |
| PAS100 green waste compost | Recycled garden waste | Moderate–high | Rare in retail MPCs but still used in bulk soil improvers. |
| Peat (legacy blends) | Mined peat bogs | Clean | Now phased out in the UK due to environmental regulations. |
PAS100 vs non-PAS materials
PAS100 certification applies only to composts derived from biodegradable waste (mainly garden or food waste). It enforces strict limits on physical contaminants, maturity, and safety testing. These composts are often sold as soil improvers, not as retail MPCs.
Non-PAS substrates (wood fibre, coir, bark fines) fall under horticultural quality assurance schemes rather than PAS100, and are typically cleaner by nature because they start from virgin materials, not recycled streams.
A fair view of PAS100 composts
PAS100 sets a credible minimum quality standard — it doesn’t guarantee perfection, but it does ensure that green waste compost is safe and stable. The specification permits small traces of glass, stones, metals, or plastics because of how garden waste is collected.
When gardeners include litter, plant labels, or plastic pots in green bins, these items are shredded during composting and become difficult to remove. Although the composting industry continually improves screening, eliminating every fragment would require multimillion-pound plant upgrades that few sites can justify under current economics.
Consumers also play a role: the price of bagged compost is tightly constrained, and even a 20–50 p rise per bag can decide whether a product sells. Until buyers are willing to pay a premium for “ultra-clean” recycled compost, PAS100 composts will remain a balanced compromise — environmentally valuable, affordable, but not flawless.
The peat-free transition: lessons learned
The UK compost industry has undergone an enormous transition over the past decade. As peat was phased out, manufacturers searched for sustainable alternatives.
Early trials with green waste (PAS100) compost revealed major challenges — inconsistency, odour, variable pH, and visible contaminants. These experiences drove major R&D investment into engineered wood-fibre, coir, and bark-based mixes that now perform consistently and cleanly across most retail brands.
In short: the peat-free composts of today are far more advanced than those from just a few years ago.
To see how these improvements show up in practice, and which mixes perform best across different uses, visit our Reviews Section — we build this expert insight into every product rating.
Disclaimer.
Brand names such as Westland, SylvaGrow, RocketGro, Dalefoot, Carbon Gold, and others mentioned on this site are registered trademarks of their respective owners. MultipurposeCompost.co.uk includes these examples for informational and comparative purposes only and does not claim endorsement, affiliation, or suitability for any specific use. Gardeners and buyers should always check current product specifications and manufacturer guidance before purchase or application.
