The best bio compost bags, compared.
Top pick: BioBizz Light Mix 20 L Best value: BioBizz Light Mix 20 L – Lower spend for about 20 litres at about £10.44, if you check the variant. The 50 litre bag is cheaper per litre. Updated October 2026.
Bio compost here means a bagged growing medium sold in the UK as organic, organic-enriched, or biologically active potting compost. It is not a food-caddy liner and not homemade heap compost. You are usually repotting houseplants, filling patio containers, or starting seeds. On the shelf, organic often means natural ingredients rather than a Association mark. Quality is an honest litre size, a feed level that matches the plant, and a mix you can wet and drain. Peat-free compost can look dry on top while the root zone is still wet, and many mixes need liquid feed sooner than old peat. Defra set 2024 as a target for banning amateur peat sales in England, but the RHS says no such ban is in legislation, so the bag's wording still decides. The checks are in the [bio compost buying guide](/hub/fertiliser-soil-and-bark-mulch/bio-compost/sub/bio-compost-buying-guide). It is the wrong material for sowing seed. None of the five amazon.co.uk listings shows that symbol.
Bio compost here means a bagged growing medium sold in the UK as organic, organic-enriched, or biologically active potting compost. It is not a food-caddy liner and not homemade heap compost.
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Personal buying guide
Question 1 of 2
What are you potting?
This 20 litre BioBizz Light Mix is the best value in this set when a couple of large pots is the job and you do not want to carry 50 litres. It is about £10.44, listed at 5 kg, with 4.6 from 122 reviews. The selected variant is 20 litres, but the title also prints 50 L and 10 L, and one reviewer received 20 litres after expecting 50 litres. The style name calls it a loamy, moisture-retaining general potting mix, and the saved listing does not list ingredients or a fertiliser analysis. One reviewer says the texture does not clump. Another says a bag arrived very dry, and one reported fungus gnats. Organic appears in the title with no certifier, and peat is not stated. At about 52p a litre it costs more per litre than the 50 litre Light Mix, which is the trade you make for a smaller sack you can get up the stairs.
Pros
Cons
Best for: You need about 20 litres for a balcony or a few pots, and you will check the variant is 20 litres before you order.
Less suitable: You are filling a run of containers, or you cannot tell the 20 litre variant from the 50 litre wording in the title.
Specifications
Common questions
Is this the 50 litre bag?
The variant in the saved listing is 20 litres, listed at 5 kg. The title also contains the words 50 L and 10 L. One reviewer received 20 litres after expecting 50 litres.
Does the listing state what the soil is made of?
The listing asks that question. The saved listing does not give ingredients. The style name says loamy, moisture-retaining general potting mix.
Do reviews mention drainage?
One reviewer says the texture does not clump. Another says a bag arrived very dry. One reviewer reported fungus gnats.
The Westland 8 litre houseplant compost is the bag to open when you are repotting one indoor plant, not when you are hunting an organic certificate. It is about £9.47, listed at 4.47 kg, with 4.5 from 4,932 reviews, the largest file in this set. The listing says 8 litres fills a 28 cm pot, claims Seramis granules and perlite, and names model 10200035, made in the United Kingdom by Westland Horticulture. It does not say organic, and it does not mention peat. Many reviewers use it for ordinary houseplants. Several report fungus gnats, springtails, or little visible perlite, drainage comments conflict, and one bag contained a piece of brick. At about £1.18 a litre it is the dearest per litre here, which is the price of a small specialist bag rather than a stronger organic claim. A review count this large is still not a lab test, and it does not make the mix peat-free.
Pros
Cons
Best for: You are repotting houseplants into about a 28 cm pot and you want a small UK-made bag with a long review file.
Less suitable: You need organic wording you can check, a 20 or 50 litre sack, or compost for sowing seed.
Specifications
Common questions
Is this compost described as organic?
The listing asks the question. The bullets do not say organic, and they do not mention peat. They do claim Seramis granules and perlite.
How much does 8 litres fill?
The listing says this 8 litre bag fills a 28 cm pot.
What do reviewers report after repotting?
Many use it for ordinary houseplants. Several report fungus gnats, springtails, or little visible perlite. Drainage comments conflict, and one bag contained a piece of brick.
The BioBizz Light Mix 50 litre bag is the top pick in this set when you are filling several pots and you want a light mix you can feed yourself. On amazon.co.uk it is about £17.15, listed at 12 kg, with 4.5 from 234 reviews. Reviewers often describe an airy texture for seedlings, and some mention tomatoes and chillies. The title says organic soil potting compost, and the saved listing names no certifier and does not say whether the bag contains peat. The listing also does not give a fertiliser analysis, so the light behaviour is what the reviews describe, not a printed NPK. At least one bag arrived with sticks, clumps, and hard pieces, and one reviewer reported mould. The manufacturer field on this listing reads Kebonds, which is a seller line rather than a second brand of mix. You are paying about 34p a litre for a stated 50 litres, the lowest price per litre here, and you still need the sack in your hands to be the 50 litre one.
Pros
Cons
Best for: You are potting several containers or starting seedlings, and you can carry a 12 kg sack.
Less suitable: You need a certified organic input, a bag that states peat-free, or a rich mix for an established plant.
Specifications
Common questions
Does the listing say this 50 litre bag contains fertiliser?
The listing asks whether it contains fertiliser and does not give an analysis. The bullets only say growing medium, feeding stage, hydroponics, plant feed, and greenhouses.
Is a certifier named for the organic wording?
No. The title says organic soil potting compost. The saved listing does not name a certifier.
What do reviewers say about the texture?
Many describe it as airy and suitable for seedlings. At least one bag was reported with sticks, clumps, and hard pieces, and one reviewer reported mould.
The DIVCHI bag is a 10 litre multi-purpose compost titled organic enriched, at about £7.70, with 4.4 from 1,702 reviews. The item weight is 680 g, and reviewers describe a small block that expands when you add water, so the 10 litre figure is a finished volume you have to make, not a loose sack you tip out. Some reviewers dispute that the expanded block reaches 10 litres. The bullets claim vermiculite, garden soil, and sand or perlite, plus a nutrient boost, and they do not give an analysis. The title's organic wording names no certifier, and peat is not stated. Country of origin on the listing is India. A 1,702-review file is the second largest here, and it still does not tell you the block will finish at 10 litres in your bucket. At about £7.70 it is the lowest shelf price in the set, and it is a poor bargain if the expanded compost falls short of the pot you planned.
Pros
Cons
Best for: You want a small, light delivery for seed trays or a few pots, and you will expand the block in stages and check the finished volume.
Less suitable: You need a loose 20 or 50 litre sack whose listed weight matches the litres on the label.
Specifications
Common questions
Is this compost described as organic?
The title says organic enriched. The saved listing does not name a certifier, and it does not state a peat content.
Why is a 10 litre bag listed at 680 g?
That is the item weight in the saved listing. The bullets do not say compressed. Reviewers describe a small block that expands when water is added, and some dispute the finished volume.
Can it be used for houseplants?
The listing says yes, for indoor and outdoor plants, seed, and potting on. It also claims vermiculite and sand or perlite.
The BioBizz All Mix 20 litre listing is the rich bag in this set. The bullets call it a strong pre-fertilised soil, at about £10.70 and 5 kg, with 4.4 from 146 reviews. That charge is the reason to buy it for a plant that is already growing, and the reason to leave it alone for a first sowing. One reviewer said tomato starters died because the mix was too rich, and another disliked the perlite. The saved listing only writes out six reviews, so the 146-count is a larger star line than the comments you can actually read here. The title says organic and names no certifier. BioBizz's blend article says All Mix contains peat-based components, so do not call this bag peat-free. No NPK or EC figure is printed. BioBizz's own page describes All Mix as heavily pre-fertilised for about a couple of weeks and tells you to moisten it and wait 36 hours before planting. That wait is the maker's instruction, not a result measured from these reviews.
Pros
Cons
Best for: You are potting on a plant that is already growing, and you can moisten the mix and leave it before you plant.
Less suitable: Seedlings, cuttings, or any young plant you cannot afford to scorch in the first week.
Specifications
Common questions
Does the listing say it is pre-fertilised?
Yes. The bullets call it a strong pre-fertilised soil mixture. No NPK or EC figure is in the saved listing.
Is organic certification named?
No. The title says organic. The saved listing does not name a certifier. BioBizz's blend article says All Mix contains peat-based components.
What went wrong in reviews?
One reviewer said tomato starters died because the mix was too rich. Another disliked the perlite. The saved listing only contains six reviews.
Five amazon.co.uk listings were scored from the stored pages and the UK review notes already on file. Shelf prices are the figures in those files. There is no laboratory test. Organic wording, a nutrient boost, Seramis, and a finished volume are the seller's claim unless a review contradicts them. None of the five files names a certifier or prints peat-free. BioBizz's blend article says All Mix contains peat-based components. That is not a peat test of the bag in your hand. The highest score is the top pick. The best value is the 20 litre Light Mix, the lower spend for a smaller job. The 50 litre bag is cheaper per litre. The weights below sum to 100.
Amazon evidence
30%Star rating on amazon.co.uk, then the size of that ASIN's review file. Westland at 4.5 from 4,932 takes the most of this block. DIVCHI at 4.4 from 1,702 is next. Light Mix 50 L at 4.5 from 234 is a mid-size file. Light Mix 20 L at 4.6 from 122 is smaller. All Mix at 4.4 from 146 loses ground because the saved listing only writes out six reviews.
Listing honesty
25%A stated litre size that agrees with the listed weight, a feed line you can act on, and organic wording you can see. The 20 L Light Mix title also prints 50 L and 10 L. DIVCHI lists 10 L at 680 g. A missing fertiliser analysis and a missing peat line apply to every row. Westland loses points here because the listing does not say organic.
Review outcome
25%Comments that match the job score higher when the sample is large enough to read. An airy Light Mix used for seedlings scores. Nutrient burn on tomato starters, a dry core, fungus gnats, a piece of brick, and a finished volume that looks short of 10 L are deductions. Six written-out All Mix reviews cannot fill this block.
Value
20%Stored GBP price against a litre figure the listing and the weight can both support. Light Mix 50 L at about £17.15 is about 34p a litre and takes this block. Light Mix 20 L at about £10.44 is about 52p a litre and a smaller cash outlay. DIVCHI is the lowest shelf price and loses most of this block because reviewers dispute the expanded volume.
Match the feed level and the real litre size before you match the star line. Prices below are the amazon.co.uk figures stored for these five listings. This is not a laboratory test.
Bio compost in this set is a bagged growing medium, not a compostable caddy liner and not heap compost from the garden. Heap compost is a soil improver. It is the wrong material for sowing seed. You are choosing a bag for houseplants, patio containers, or young plants, and the label word organic often means natural ingredients rather than a Soil Association Approved input. Garden Organic makes that distinction. None of the five amazon.co.uk listings in this comparison shows that symbol.
This page is bagged potting compost. A compostable food-caddy liner will not fill a pot. Heap compost is a soil improver, not seed compost.
The 20 litre Light Mix title also prints 50 L and 10 L. One buyer expected 50 litres. Read the selected variant and the listed weight.
All Mix is heavily pre-fertilised for about a couple of weeks. One reviewer said tomato starters died because the mix was too rich. Use Light Mix for a first sowing.
Seedlings and cuttings want a light charge. BioBizz describes Light Mix as lightly fertilised, for control with liquid feed from early on. The amazon files for both Light Mix sizes do not print an NPK analysis, so that light behaviour is the maker's description plus reviews that call the mix airy. All Mix is heavily pre-fertilised for about a couple of weeks. The maker says to moisten it and leave it 36 hours before planting, and the listing calls it a strong pre-fertilised soil.
Read the variant you have selected. Light Mix 20 L is about £10.44 at 5 kg, and the title also prints 50 L and 10 L. Light Mix 50 L is about £17.15 at 12 kg, about 34p a litre, the lowest here. All Mix 20 L is about £10.70 at 5 kg, about 54p a litre. DIVCHI is about £7.70, listed as 10 L at 680 g. Reviewers describe a block that expands, and some say it looks short of 10 litres, so the low shelf price is not the best value. Westland is about £9.47 for 8 L, about £1.18 a litre.
Three typical situations, each with a recommendation from this comparison.
Seedlings and cuttings want a light charge, then liquid feed from early on. BioBizz Light Mix 50 L is the top pick at about £17.15, listed at 12 kg, with 4.5 from 234 reviews. Reviewers describe an airy mix. The title says organic and names no certifier, and peat is not stated. You need to be able to carry 12 kg.
About 20 litres is enough for a couple of large pots, and you do not have to carry 50 litres. BioBizz Light Mix 20 L is the best value at about £10.44, with 4.6 from 122 reviews. The title also prints 50 L and 10 L. Check the variant is 20 litres before you order.
An 8 litre bag is the right size for one indoor pot. Westland houseplant compost is about £9.47, with 4.5 from 4,932 reviews, and the listing says 8 litres fills a 28 cm pot. It claims Seramis and is made in the United Kingdom. It does not say organic, and it does not mention peat.
The top pick is BioBizz Light Mix 50 L at about £17.15. The listing states 50 litres at 12 kg, amazon.co.uk shows 4.5 from 234 reviews, and the price is about 34p a litre. Reviewers describe an airy mix for seedlings. The best value is Light Mix 20 L at about £10.44 when you only need about 20 litres and you check the variant, which also prints 50 L and 10 L. Westland 8 L has the largest review file and does not say organic. DIVCHI is the lowest shelf price, and reviewers dispute the finished volume. All Mix is the rich bag, and one reviewer lost tomato starters. None of these scores is a laboratory test.
BioBizz Light Mix 20 L
Lower spend for about 20 litres at about £10.44, if you check the variant. The 50 litre bag is cheaper per litre.
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 the amazon.co.uk figures stored for these five listings. Organic wording is not a certifier. All Mix's peat line is the maker's blend article, not a test of the bag in your hand. No ban on amateur peat sales is in legislation.
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.
