TL;DR

Compost quality can vary — mainly due to how it’s made and what goes into it. PAS100 is the official UK minimum compost standard. It keeps compost safe and consistent. Retail brands often go further, with tighter in-house checks for texture, cleanliness, and nutrients. A few small bits of wood, plastic, or glass are allowed under PAS100, but premium brands usually keep these to a minimum. Knowing these differences helps you understand how our review scores are set — and what to expect from different products.

Why Quality Standards Matter

Most composts sold in the UK are good quality, but not all are the same.

When we review composts, we look at how clean, smooth, and reliable they feel to use. Behind those scores are formal quality checks that guide both compost makers and retailers.

This page gives you the basics — no science lecture, just what you need to know to buy with confidence.

PAS100 – The Minimum UK Standard

PAS100 (Publicly Available Specification 100) is the national standard for compost quality. It sets out how compost should be made and what it must pass before it can be sold:

• Temperature and process control – to kill weed seeds and diseases.
• Contaminant limits – keeps plastics, glass, and metal below strict thresholds.
• Maturity and stability – makes sure compost is safe for plants.

If a compost is PAS100-certified, it’s passed these checks. But PAS100 is a minimum. It allows trace amounts of small fragments that are harmless but not ideal for bagged retail use.

Retail QA – Going a Step Further

Retail compost brands (like Westland, SylvaGrow, RocketGro, and Dalefoot) usually add their own quality tests on top of PAS100. They focus on what gardeners notice most:

• Extra fine screening for smoother texture.
• Lower tolerance for contaminants than PAS100.
• Batch testing for nutrients and pH so each mix performs the same.
• Checks for smell and appearance so every bag looks and feels right.

PAS100 sets the floor; retail QA raises the bar.

When you see cleaner compost in a premium bag, that’s because these brands invest in those extra checks.

Green Waste vs Premium Retail Blends

Compost made from council green waste can fully meet PAS100, but may still include small bits of wood, plastic, or glass within legal limits. Premium retail composts usually start with cleaner ingredients and use tighter screening.

That’s why we separate budget and premium products in our reviews — not as a criticism, but to show the difference in how they’re made and tested.

Cross-link: Premium vs Budget Compost →

Why Occasional Issues Still Make the News

Every so often, you might hear about compost problems — like herbicide residues in manure-based composts. These cases are rare but they remind everyone why standards exist.

• PAS100 gives traceability so issues can be tracked and corrected.
• Retail QA adds another safety layer through extra batch checks.

For the in-depth science behind standards, visit HealthySoil: Compost Standards & Safety →.

How We Use These Standards in Our Reviews

Our AI-assisted scoring looks at the same things gardeners care about:

• Cleanliness & texture – how smooth, crumbly, and pleasant to handle it is.
• Consistency – whether it’s uniform from bag to bag.
• Transparency – whether the brand explains what standards it meets.

These standards shape how we score each compost — so you can see at a glance which brands deliver quality you can trust.

Summary

Compost quality comes down to two layers:

• PAS100: the baseline that keeps compost safe and standardised.
• Retail QA: the extra care that makes premium compost cleaner and more reliable.

Understanding both helps you read our reviews with confidence — and pick a compost that suits your plants and your expectations.