The best Seramis granules, compared.
Top pick: COMPO pumice granules 6 L Best value: Westland orchid mix 4 L – Lowest bag price at about £7.29, with the deepest review file here, 4.6 from 8,049. Updated October 2026.
Seramis granules are the clay granules many people in the UK buy when a houseplant pot stays wet, a cachepot has no hole, or tiny flies keep coming back to the compost. In the shops that name covers more than one material. Fired open-pore clay is for a watertight pot: the root ball stays intact, and the grain holds water in its pores. Expanded clay pebbles are sold as a top dressing, a crocking layer, a mix into compost, or a humidity tray. Pumice is a fine volcanic grit used on its own, blended in, or spread as a thin cap. Some bags are ordinary potting compost that only lists clay granules as one ingredient. A suitable bag matches the job. Check that the stated volume in litres agrees with the pack data, and treat peat-free as real only when those words are printed. Reviews help when they describe the substrate, the dust and the fill. How the four types differ is set out in the [Seramis granules buying guide](/hub/fertiliser-soil-and-bark-mulch/seramis-granules/sub/seramis-granules-buying-guide).
Seramis granules are the clay granules many people in the UK buy when a houseplant pot stays wet, a cachepot has no hole, or tiny flies keep coming back to the compost.
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Personal buying guide
Question 1 of 2
Do you want loose granules or a ready mix?
The COMPO bag is 6 litres of 2–5 mm natural pumice at about £29.78, sold as a substrate, a mix or a top dressing. Across 319 amazon.co.uk ratings it sits at 4.7, but the first 50 reviews are almost all from other Amazon marketplaces, not UK reviews. Those buyers used it on succulents, lemon and indoor mixes, and several said the grain held moisture while staying lighter, and cooler in sun, than expanded clay. The same reviews split on grade: some bags arrived with many small pieces, others with large lumps, and a few wanted a coarser drainage size than the printed 2–5 mm. One recurring note is a wet, dark bag that dried paler in an open bucket. At about £5 a litre this is a named mineral, not cheap volume. A listing bullet calls it a lower-CO2 alternative to conventional clay granules. That is the manufacturer's claim.
Pros
Cons
Best for: A named 2-5 mm pumice bag for indoor or balcony mixes.
Less suitable: Anyone who wanted cheap volume or a UK review file.
Specifications
Common questions
What grain size does the listing state?
A bullet states a grain size of 2-5 mm.
Is this clay or pumice?
The item is pumice stone granules. The listing calls it a lower-CO2 alternative to conventional clay granules. That is the manufacturer's claim.
Does the listing mention fungus gnats?
A bullet says it prevents pest infestation such as fungus gnats. That is a manufacturer claim, not a result measured for this page.
Westland's 4 litre orchid mix is pine bark plus Seramis at about £7.29, and a bullet says it fills a 14 cm pot. It is the deepest review file in this comparison: 4.6 from 8,049, with reviews from the United Kingdom. Reviewers report new leaves and flower stems after a repot, use it for years on old orchids, and several pick the Seramis out for a sick Phalaenopsis. One bag often covers more than one plant. The recurring criticism is density: some call the mix dirt-like or too full of crushed bark and fines, and they sort chips or add perlite. One order was substituted for Miracle-Gro, and an older review said the mix held peat and stayed wet. The listing does not print peat-free, even though the manufacturer site does. This is a specialist orchid compost, not a reusable loose-granule system.
Pros
Cons
Best for: A small orchid repot when you want pine bark plus Seramis and a large UK review file.
Less suitable: A general houseplant compost or a reusable loose-granule system.
Specifications
Common questions
What is in the mix?
The bullets name Seramis granules for water and nutrient availability and pine bark for airflow and drainage.
How much pot does 4 litres fill?
A bullet says this 4 L bag will fill a 14 cm pot.
Does the listing say it is organic?
The question appears on the listing. The bullets do not name a certification. Organic would not mean peat-free.
Westland Hydroleca is a 10 litre bag of ceramic clay pebbles with a dense skin and honeycomb core, at about £13.55. The amazon.co.uk line is 4.6 from 569 reviews, and the reviews are from the United Kingdom. That is the deepest loose-granule review file in this comparison. Buyers use it as a pot topper, a crocking layer, a mix-in and a humidity tray. Several said a clay-ball cap reduced tiny flies on orchids, and others washed the pebbles and found little dust. The bag is not a single ball size: reviewers report small and large pebbles together. Some still call the price high, even when they found it cheaper than a garden-centre bag, and the unit count is 1 against a 10 litre title. This is expanded clay for drainage and humidity, not a closed-pot Seramis store.
Pros
Cons
Best for: Indoor or outdoor pots when you want a named UK Hydroleca bag for topping, crocking or a mix.
Less suitable: A closed-pot Seramis system or a specialist orchid bark mix.
Specifications
Common questions
What are the granules made of?
The bullets say lightweight ceramic clay pebbles with a smooth dense outer skin and a honeycomb interior.
Can they be used outdoors?
The listing says they are for the tops of pots on house plants as well as outdoors, and for greenhouse benches.
What does the listing say about pH?
A bullet states that pH and EC are stable.
UK GROW's 4 litre cactus and succulent mix names Seramis, grit and sand, prints peat-free, and sits at about £10.29. A bullet says it fills a 14 cm pot. The amazon.co.uk line is 4.6 from 166, shared with the 50 litre bag. Reviewers liked the light, airy texture on repotted cacti, baby aloes, cuttings and a yucca, and some sat pots in a tray to take water up. The same pool reports short volume on smaller packs, spilled bags, unlabelled black buckets, and one rotten-egg smell that sent the mix in the bin. One buyer said it did not revive an ailing cactus. Treat the 4.6 as a shared line, not a 4-litre-only test.
Pros
Cons
Best for: A small cactus or succulent repot that names Seramis and peat-free.
Less suitable: A large bed, or anyone who needs a labelled sack.
Specifications
Common questions
Is the listing peat-free?
Yes. The title says peat free.
What does the mix add for drainage?
A bullet names added grit and sand as well as Seramis granules.
The 50 litre UK GROW cactus mix is the same peat-free Seramis, grit and sand blend as the 4 litre bag, at about £34.99 and a listed 20 kg. Title and unit count both read 50 litres, which is cleaner than the houseplant line's clash between a litre title and a unit count of 1. Stars remain 4.6 from 166, and the reviews are the shared pool: new growth on cacti and aloes, a light mix, and at least one delivery in a large plastic pot. Volume complaints in that pool often name 2 litre or 3 litre packs, not this sack, so they do not prove a short 50 litre fill. Packaging and a rotten-egg smell still sit in those same reviews. This is a many-pot buy only if you can lift 20 kg and accept a shared review set.
Pros
Cons
Best for: Many cactus or succulent pots if you want one peat-free mix that names Seramis.
Less suitable: A single 14 cm pot, or anyone who cannot lift 20 kg.
Specifications
Common questions
What volume is this listing?
The title and the unit count both read 50 litres. Listed weight is 20 kg.
Are the reviews unique to the 50 L bag?
No. The reviews match the 4 L cactus listing. The listing line is 4.6 from 166.
Topline's citrus mix arrives as two 10 litre bags at about £20.00, with Seramis named and peat-free on a bullet. The listing line is 4.6 from 14, and six reviews were read. Those reviewers planted lemon and orange, and one described an orange tree as rejuvenated and new growth on a lemon within a week. Others liked the bag size and called the mix well balanced. One bag arrived split in transit, and one buyer did not believe the bags were 10 litres. The unit count is 6,000 g against a 2 × 10 L title, and listed weight is 6 kg, so the volume claim is the weak point. This is a citrus potting compost, not loose clay. The fruit and watering claims on the title are manufacturer lines, not measured results in the reviews.
Pros
Cons
Best for: A lemon, orange or lime in a pot when you want a Seramis-named citrus mix.
Less suitable: Loose clay granules, or anyone who needs a deep review file.
Specifications
Common questions
How many bags arrive?
The title says 2 x 10 L. The number of packs is 2.
Is it peat-free on the listing?
Yes. A bullet says peat free.
Does the listing name lime trees?
Yes. A bullet lists lemons, oranges, limes and other citrus trees.
Invigortex is a 1 litre, 550 g pack of washed LECA grit at about £7.49, sold to blend at 20–50 per cent or to use as a top layer. The listing line is 4.2 from 13, and four reviews were read. Those reviewers used it on houseplants that had been overwatered in winter, including a pink philodendron, and liked that roots were not sitting in water. One treated it as a clean top dressing. The main complaint is the pack itself: they wanted a larger bag. At about £7.50 a litre this is a trial, not a volume buy. Ten litres of Hydroleca in this comparison is the cheaper pebble bag. The listing says rinse, sterilise and reuse. It does not give a millimetre grade.
Pros
Cons
Best for: A 1 litre LECA trial for one or two pots or a top dressing.
Less suitable: Filling many pots. The 10 L Hydroleca bag is the volume bag here.
Specifications
Common questions
Is it reusable?
A bullet says rinse, sterilise and reuse.
Can it be mixed into compost?
A bullet says blend 20-50 per cent into potting soil for orchids, aroids, succulents and bonsai.
Does the listing mention fungus gnats?
A bullet says it is useful as a top layer to deter fungus gnats. That is the manufacturer's claim.
The 9 litre UK GROW houseplant bag is the smaller sibling of the 20 litre and 40 litre mixes, at about £10.79, with Seramis and perlite named in the bullets. Stars are 3.5 from 51, shared across those three sizes, so this is not a 9-litre-only file. Reviews praise drainage and a well-balanced mix, including one order that arrived in a hard tub. The same reviews describe unmarked bags, a box that fell apart, missing composition labels, and dry, crumbly compost. Title and volume say 9 litres. The unit count is 1. It is a one-or-two-pot bag if you want the named mix and will accept a thin, shared review set. The listing does not say peat-free.
Pros
Cons
Best for: One or two houseplant repots if you want the named mix in a smaller bag.
Less suitable: Anyone who needs a labelled sack or a deep review set.
Specifications
Common questions
What volume is this listing?
The title and volume field say 9 litres. The unit count is 1.
Does it include perlite as well as Seramis?
Yes. The bullets name Seramis granules and added perlite.
UK GROW's 20 litre houseplant mix names Seramis granules and perlite and sits at about £14.99, about 75p a litre. The amazon.co.uk line is 3.5 from 51, and the reviews are the same pool as the 9 litre and 40 litre bags, so this is not a separate review sample. Some buyers liked the drainage and called the blend well balanced, including on a palm. One order came in a hard plastic tub with a lid. The louder complaint is packaging: unmarked or brandless sacks, cling film, a box held with tape, split packs and compost with no composition label. Several called the mix dry, crumbly and poor. The unit count is 1 against a 20 litre title. The bullets say feed for about six weeks, then a liquid. The listing does not say peat-free.
Pros
Cons
Best for: A bulk houseplant mix that names Seramis, if you accept a thin, shared review file.
Less suitable: Anyone who needs a labelled sack or a deep UK review set.
Specifications
Common questions
Does this bag name Seramis?
Yes. The title and bullets say the mix is blended with water-retaining Seramis granules and perlite.
How long does the listing say the feed lasts?
A bullet says the mix has enough nutrients for about six weeks, then you should feed with a liquid.
Does the listing say peat-free?
No. That wording is not in the listing bullets.
The 40 litre UK GROW houseplant mix is the bulk bag in this line, at about £23.99 and a listed 16 kg, with Seramis and perlite in the bullets. The star line is still 3.5 from 51, and the reviews match the 9 litre and 20 litre listings. Praise in that pool is the same: drainage from the granules, a balanced mix, and at least one hard tub. Complaints are the same too: unmarked sacks, split packs, no composition label, and dry, crumbly compost. Title and volume say 40 litres. The unit count is 1. This only makes sense if you have many pots and will live with a shared review file, not if you wanted one labelled 14 cm refill. The listing does not say peat-free.
Pros
Cons
Best for: Many houseplant pots if you want one large mix that names Seramis.
Less suitable: A single 14 cm pot, or anyone who needs a labelled sack.
Specifications
Common questions
What volume is this listing?
The title and volume field say 40 litres. The unit count is 1. Listed weight is 16 kg.
Are the reviews unique to the 40 L bag?
No. The reviews match the 9 L and 20 L UK GROW houseplant listings. The listing line is 3.5 from 51.
Ten amazon.co.uk listings were scored from the stored pages and the review notes stored with those listings. There is no laboratory test. Each row starts from the listing star line. A type label is the product type printed on that listing. Volume agrees only when the title, the volume field and the unit count match. Peat-free is recorded only when those words appear on that listing. The top pick is the deepest loose-granule review file that is still clay media. The best value is the lowest bag price together with the deepest review file. UK GROW houseplant sizes share one 3.5 from 51 pool. The cactus sizes share one 4.6 from 166. The weights below sum to 100.
Type and job
25%Open-pore clay, expanded clay, pumice and a Seramis-named compost are different products. A closed pot, a drainage layer and a ready mix for one plant group are not one ladder.
Volume agreement
20%The stated litres count when the title, the volume field and the unit count say the same thing. A 14 cm pot line is a size claim, not that match.
Peat-free wording
10%Only the words peat-free on that listing count. Organic is not peat-free, and a manufacturer page does not fill a gap on the amazon.co.uk bullets.
Review evidence
25%Star rating on amazon.co.uk, then how deep that file is and whether the texts are about this bag. A shared pool across sizes is one file, not three.
Price per litre
20%Pounds per litre from the stored shelf price and the stated volume, as a rule of thumb. A small grit bag is a trial, not a volume buy.
Buy the type before you buy the star line. Open-pore clay, expanded clay, pumice and a compost that names Seramis are not one list. Prices below are amazon.co.uk shelf prices from the stored listings. This is not a laboratory test.
Seramis granules on a UK listing are not one material. Fired open-pore clay, expanded clay pebbles, pumice, and a compost that only names clay granules as an ingredient do different jobs. Buy the type before you buy the star line. Prices below are amazon.co.uk shelf prices from the stored listings. This is not a laboratory test. Open-pore fired clay is the closed-pot system.
Hydroleca and LECA are expanded pebbles. Pumice is a volcanic grit. Several bags are compost that only names Seramis as one ingredient. The job comes before the price.
The UK GROW houseplant 9, 20 and 40 litre bags share 3.5 from 51. The cactus 4 and 50 litre bags share 4.6 from 166. One pool is one pool.
About 75p a litre and about £7.50 a litre can both be a sensible buy, for a large compost and a 1 litre trial. Compare type and litres.
Name the material first. Open-pore fired clay is the closed-pot system: root ball left on, about one third granules underneath, water at about a quarter of the pot, and a moisture indicator. The manufacturer states more than 80 per cent pore volume. Expanded clay is the pebble you use for a top dressing, crocking, a mix or a humidity tray. Westland also describes a 2 cm layer on a greenhouse bench. Pumice in this comparison is a 2–5 mm grit for neat use, a mix or a thin cap.
Volume agrees only when the title, the volume field and the unit count match. Several houseplant bags say 9, 20 or 40 litres in the title and 1 in the unit count. The citrus pair says 2 × 10 litres and lists 6,000 g. The 50 litre cactus bag is the cleaner large sack: title and unit count both read 50 litres, at a listed 20 kg. A bullet that fills a 14 cm pot is a size claim beside that check, not a substitute for it. Peat-free is the words on that listing.
Three typical situations, each with a recommendation from this comparison.
You want clay pebbles for a top dressing, a crocking layer, a mix or a humidity tray, including where tiny flies bother the compost surface. Westland Hydroleca 10 L is the top pick at about £13.55, with 4.6 from 569 reviews. It is expanded clay. It is not a closed-pot Seramis system, and the ball size in the bag varies.
You have a moth orchid in about a 14 cm pot and want pine bark plus Seramis, not loose pebbles. Westland orchid mix 4 L is the best value at about £7.29, with 4.6 from 8,049 reviews. Some buyers find it dense and sort out fines. The listing does not print peat-free.
You want to try expanded clay on one or two pots, blended at 20–50 per cent or used as a top layer, and you will rinse it. Invigortex LECA grit is 1 litre at about £7.49, about £7.50 a litre, with 4.2 from 13 reviews. For many pots, the 10 litre Hydroleca bag is the volume buy.
The top pick is Westland Hydroleca 10 L at about £13.55. It is expanded clay, 4.6 from 569 reviews, and the deepest loose-granule file that is still clay media. Use it for topping, crocking, a mix or a humidity tray. It is not a closed-pot Seramis system, and it does not name Seramis. The best value is Westland orchid mix 4 L at about £7.29, the lowest bag price, at 4.6 from 8,049 reviews. COMPO pumice has the higher star line, 4.7 from 319, at about £29.78, and the first reviews are not a UK sample. None of these scores is a laboratory test.
Westland orchid mix 4 L
Lowest bag price at about £7.29, with the deepest review file here, 4.6 from 8,049.
Editorial
Peter F. is the editor for DIY & tools at productscompared.co.uk. Comparisons in this category are checked against amazon.co.uk listings, review evidence and public UK sources.
Guides on what to look for, how to use a product, and common mistakes.
Public UK and maker sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the ten amazon.co.uk listings in the stored pages. A gnat, watering or CO2 line is the manufacturer's claim. Peat-free means those words on that listing. This is not a laboratory test.
Expert source (DIY & tools): Lee Burkhill (Garden Ninja) (external profile) – public expert commentary used as a research source, not as a contributor to our pages.
This page contains affiliate links to amazon.co.uk (tag pcuk26-21). If you buy through them, we may earn a commission at no extra cost to you. Prices, stars and review counts are from the listings. This is not a laboratory test.
