The best biochar soil improvers, compared.
Top pick: McMillan Biochar 10L Best value: EarthCraft Blends Bio Char Soil Improver for Plants (40 Litre) – Lowest price per stated litre among packs whose weight scales in the family, about 85 pence at about £33.98. Updated October 2026.
Biochar is a bagged soil improver: biomass carbonised with little oxygen, sold to mix into compost, pots and beds. The Royal Horticultural Society describes the solid as at least 80% elemental carbon that does not readily decompose, and treats straight char as a physical conditioner rather than a feed. Listings often leave out feedstock, pH and any certificate. Quality is a litre claim that matches the weight, a clear line on whether the char is already charged, and a bag that is not unnamed black dust. What to check before you pay is in the [biochar buying guide](/hub/fertiliser-soil-and-bark-mulch/biochar/sub/biochar-buying-guide). This page does not rank carbon sequestration, and it does not treat the word organic as a certification.
Biochar is a bagged soil improver: biomass carbonised with little oxygen, sold to mix into compost, pots and beds.
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Personal buying guide
Question 1 of 2
What are you mixing?
McMillan’s 10 litre bag is £26.95 and lists 4 kg, about 400 g per litre, the heaviest 10 litre claim in this set and the only listing that says the char is pure wood. The form line is granules and powder. Coverage is printed as one bag for 20 square metres of vegetable garden or for 100 litres of soil, which are two different rates, and no NPK sits beside the slow-release organic fertiliser wording. The star line is 5.0 from 2 reviews; the saved listing holds one short UK review that says the product was as described. Country of origin is Italy. Two ratings cannot carry a quality ranking, and the page shows no pH, European Biochar Certificate class or Soil Association number.
Pros
Cons
Best for: A 10 litre wood char for a small veg bed when you want the heavier listed weight and can ignore a two-review score.
Less suitable: A ranking based on stars alone, or a certified-organic site that must approve an input.
Specifications
Common questions
What feedstock does the listing name?
Pure wood. The form is given as granules and powder.
How much ground does one bag claim to cover?
The listing says one bag suits a 20 square metre vegetable garden or 100 litres of soil. It does not say which rate applies when.
Can the listing be read as a measured fertiliser analysis?
It calls the product a slow-release organic fertiliser. No NPK figures are printed in the saved listing.
Black Gold’s 1 litre listing is £7.99, with the country of origin given as the United Kingdom and activated in the title. The volume field says 1 litre and the unit count says 1,000 ml, which agree with each other, while the item weight of 1 kg is the same figure printed on the 3 litre and 5 litre siblings, so it does not scale. The 4.6 from 16 reviews is shared across those three ASINs. Captured review themes are thin and mostly positive: hanging baskets mixed with compost, a chilli in compost, and a comment that a little goes a long way, plus one note that it matched another listing. The included line describes a sealed resealable bag. Feedstock, pH and any certificate are still missing, and the page does not print a separate charging recipe.
Pros
Cons
Best for: A first indoor or patio pot when you want the small Black Gold listing whose litre fields match.
Less suitable: A bed that needs tens of litres, or a label that names the wood.
Specifications
Common questions
Does the listing say it can be used indoors?
The title says indoor and outdoor, and the bullets name potting soil as well as beds and borders.
Is it described as activated?
Yes. The title says activated. The saved listing does not describe a separate charging step.
Do the stars apply only to this size?
The saved listings for the 1, 3 and 5 litre Black Gold ASINs show the same 4.6 from 16 reviews and the same review texts.
The 3 litre Black Gold listing is £10.99, about £3.66 per litre if the title volume is what you receive. The specification volume says 3 litres, but the unit count stays at 1,000 ml and the item weight stays at 1 kg, the same weight as the 1 litre ASIN. Stars are the shared 4.6 from 16, not a fresh sample for this fill. Reviewers in that pool talk about baskets and a chilli grown in compost, not about a measured 3 litre result. Country of origin is the United Kingdom and the title says activated, without a printed soak or compost-tea step. It is the step up from a single pot when you accept that the gram fields do not prove the bag is three times the 1 litre pack.
Pros
Cons
Best for: Hanging baskets and a few pots when 1 litre is tight and you will check the fill on arrival.
Less suitable: A buyer who needs the kilogram to match the litres before ordering.
Specifications
Common questions
Does the listing say it can be used indoors?
The title says indoor and outdoor, and the bullets name potting soil as well as beds and borders.
Is it described as activated?
Yes. The title says activated. The saved listing does not describe a separate charging step.
Do the stars apply only to this size?
The saved listings for the 1, 3 and 5 litre Black Gold ASINs show the same 4.6 from 16 reviews and the same review texts.
The 5 litre title is £14.99, about £3 per stated litre, the lowest Black Gold price per litre in this set. The volume field on this ASIN is blank, the unit count is 1,000 ml and the item weight is again 1 kg, so the specification fields disagree about how much char is in the bag. The 4.6 from 16 reviews is shared with the 1 litre and 3 litre listings. The included-components line still describes one resealable bag of carbonised biochar, and the bullets name potting soil, beds and borders, indoors and outdoors. No feedstock is named. Treat the 5 litre words in the title as a claim to check on arrival, not as a weighed specification.
Pros
Cons
Best for: A mid step between a trial litre and a 10 litre sack, if the delivered bag matches the title.
Less suitable: Anyone who will only order when volume, millilitres and kilograms agree.
Specifications
Common questions
Does the listing say it can be used indoors?
The title says indoor and outdoor, and the bullets name potting soil as well as beds and borders.
Is it described as activated?
Yes. The title says activated. The saved listing does not describe a separate charging step.
Do the stars apply only to this size?
The saved listings for the 1, 3 and 5 litre Black Gold ASINs show the same 4.6 from 16 reviews and the same review texts.
At £33.98 for a title volume of 40 litres and a listed weight of 4.2 kg, this is the lowest price per stated litre in the set, about 85 pence. The weight scales with the 1 litre and 10 litre EarthCraft rows at about 105 g per litre. The 4.0 from 16 reviews is the same shared pool, so the dusty, torn-bag and charcoal-like comments travel with this size too. The bullet list of pack sizes names up to 30 litres and does not mention 40 litres. No feedstock or certificate is printed. You get the most stated volume for the money here, provided you handle a fine grade outdoors and you do not need a wood species on the label.
Pros
Cons
Best for: The largest consistent EarthCraft fill when you are blending compost outside and watching the price per litre.
Less suitable: Indoor use, or a buyer who wants chunkier pieces and a named feedstock.
Specifications
Common questions
Does the listing claim it holds water?
The bullets say it retains moisture while still letting excess water drain. They do not give a measured rate.
Is a certified-organic mark shown?
No certifier is named in the listing.
What size is this ASIN?
This listing is the 40 litres, item weight 4.2 kg version. The 4.0 rating from 16 reviews is shared with the other EarthCraft sizes in this set.
The 10 litre EarthCraft bag is listed at £16.99 and 1.05 kg, about £1.70 per stated litre if you accept the title volume. That weight is about ten times the 1 litre pack’s 105 g, so the family is consistent at roughly 105 g per litre, and much lighter than McMillan’s 4 kg for the same stated 10 litres. The same shared 4.0 from 16 reviews applies, including the fine dust, torn-bag and crushed-charcoal comments. The listing does not name a feedstock, a pH or a charging step, and the unit-count field shows an unusable 99999 g figure. The volume line in the specification block is blank even though the title says 10 litres. It suits a compost blend only if you are buying the light grade the kilograms describe.
Pros
Cons
Best for: A mid-size outdoor compost blend when a light, fine grade is acceptable.
Less suitable: A kitchen mix, or a comparison that assumes every 10 litre bag weighs about 4 kg.
Specifications
Common questions
Does the listing claim it holds water?
The bullets say it retains moisture while still letting excess water drain. They do not give a measured rate.
Is a certified-organic mark shown?
No certifier is named in the listing.
What size is this ASIN?
This listing is the 10 litres in the title, item weight 1.05 kg version. The 4.0 rating from 16 reviews is shared with the other EarthCraft sizes in this set.
EarthCraft’s 1 litre listing is £7.99 and weighs 105 g on the page, the light end of this set for a named litre. The bullets describe aeration, drainage and moisture holding for compost, pots and beds, and they do not say the char is activated or already charged. The 4.0 rating from 16 reviews is shared with the 10 litre and 40 litre EarthCraft ASINs, so those stars are not a separate sample for this size. Reviewers in that shared pool describe a fine, dusty grade, a torn bag and charcoal-like fines, and some also say the contents matched the listing. Feedstock is not named. A 1 litre trial is a small spend, though 105 g will not behave like McMillan’s much heavier 10 litre bag if you were expecting dense lumps.
Pros
Cons
Best for: A cheap first mix in one or two outdoor pots, if you can keep the dust off the patio.
Less suitable: Indoor repotting, or a buyer who wants named wood and a heavier grade.
Specifications
Common questions
Does the listing claim it holds water?
The bullets say it retains moisture while still letting excess water drain. They do not give a measured rate.
Is a certified-organic mark shown?
No certifier is named in the listing.
What size is this ASIN?
This listing is the 1 litre, item weight 105 g version. The 4.0 rating from 16 reviews is shared with the other EarthCraft sizes in this set.
The Potting Pantry listing, at £16.95, is the only bag in this set that prints a charging step: mix the char with compost, worm castings, liquid feed or nutrient-rich water before you plant. The title says activated biochar and 10 litres, and the bullets name houseplants, containers and raised beds. The model number is TPP-BIOCHAR-1L, the unit count is 280 g and the item weight is 310 g, so the litre claim and the gram fields do not describe the same pack. Feedstock, pH and a certificate are absent. The saved listing has no star rating and no review text, so there is no amazon.co.uk buyer record for dust, bag strength or fill. You cannot price it per litre until that conflict is resolved.
Pros
Cons
Best for: A windowsill trial only if the seller confirms the fill before you pay, and you still plan to charge it.
Less suitable: Anyone pricing a 10 litre sack, or a bed mix that needs a known weight.
Specifications
Common questions
Does this listing say to charge the biochar first?
Yes. The bullets say to mix it with compost, worm castings, liquid feed or nutrient-rich water before use, then blend it through the potting mix.
Is the pack definitely 10 litres?
The title says 10 litres. The model number is TPP-BIOCHAR-1L, the unit count is 280 g and the item weight is 310 g. The saved listing does not resolve that conflict.
What is the amazon.co.uk star rating?
The saved listing has no customer-review line and no review text.
Eight amazon.co.uk listings were scored from the stored pages and the review themes already on file. Shelf date 19 October 2026. There is no laboratory test. Stars are one shared pool per family. A line with no stars scores 0. Two ratings are capped, so 5.0 from 2 does not outrank 4.6 from 16. Conflicts between title litres and grams cost points. Price per stated litre is used only where the title volume is usable. The highest score is the top pick. The best value is the lowest price per stated litre among packs whose weight scales inside the family. The weights below sum to 100.
Amazon signal
35%Stars and review count, with one shared pool per family. A line with no stars scores 0. Two ratings are capped, so 5.0 from 2 does not outrank 4.6 from 16.
Listing consistency
25%Feedstock named, volume and weight that agree, origin, a charging line, and a resealable-bag line. Conflicts such as title litres versus grams, a 1 kg weight copied across sizes, or a blank volume field, cost points.
Review sentiment
20%Themes in the captured texts. Dust, a torn bag and a charcoal complaint lower the score. A thin positive pool scores higher than no text. It is not a count of stars again.
Value for the stated job
20%Price per stated litre only where the title volume is usable. A size conflict blocks that calculation. EarthCraft 40 litres is about 85 pence per stated litre on that rule.
Match the job and the pack size before you match the star line. A 1 litre trial, a dusty 40 litre bag and a heavier wood char are not one ladder. Prices below are amazon.co.uk shelf prices in this set, dated 19 October 2026. This is not a laboratory test.
Biochar in this UK comparison is a bagged soil improver. It is biomass carbonised with little oxygen, sold to mix into compost, pots and beds. The Royal Horticultural Society describes the solid as at least 80% elemental carbon that does not readily decompose, and treats straight char as a physical conditioner rather than a feed. Shoppers on amazon.co.uk are choosing among trial bags at about £7.99 and larger bags up to about £33.98. Many listings leave out feedstock, pH and a certificate.
None of the kept ASINs shows an EBC class or a Soil Association number. The European Biochar Certificate is voluntary in the UK. A certification on another brand’s improver does not transfer to these listings.
Activated on Black Gold and The Potting Pantry is a title word. The Potting Pantry bullets still say to mix the char with compost, worm castings, liquid feed or nutrient-rich water before you plant.
EarthCraft’s 10 litre bag lists 1.05 kg. McMillan’s 10 litre bag lists 4 kg. The Potting Pantry title says 10 litres beside gram fields under 1 kg. Skip the per-litre sum until volume and weight describe the same pack.
Start with the job. A 1 litre bag suits a few pots. A 10 to 40 litre bag suits a compost mix or a small bed, not an allotment plot. If the bag is plain char, plan a charging step. Activated is not that step. The Potting Pantry listing says to mix the char with compost, worm castings, liquid feed or nutrient-rich water first. Black Gold says activated and prints no separate recipe. Plain char can hold nutrients you have just applied until it is charged. Then check litres against kilograms.
Feedstock, pH, NPK and a certificate are missing on the kept ASINs. Only McMillan says pure wood. No ASIN shows an EBC class or a Soil Association number. The RHS says you should know the feedstock, and that alkaline char with a pH over 7 is a poor match for ericaceous plants and anywhere you do not want the soil sweeter. These bags print no pH. McMillan also calls the bag a slow-release organic fertiliser and prints no NPK.
Three typical situations, each with a recommendation from this comparison.
You want a small bag whose litre fields match, for one indoor or patio pot. Black Gold 1 litre is the top pick at about £7.99. The volume says 1 litre and the unit count says 1,000 ml. Origin is the United Kingdom, and the shared rating is 4.6 from 16 reviews. The 1 kg weight does not scale to the larger Black Gold sizes.
You are blending compost outside and watching the price per stated litre. EarthCraft 40 litres is the best value at about £33.98, about 85 pence per stated litre, listed at 4.2 kg. The 4.0 from 16 reviews is shared, and reviewers describe fine dust and a torn bag. Keep it outdoors.
You want a 10 litre bag that says pure wood and lists a heavier weight. McMillan Biochar 10L is about £26.95 and lists 4 kg, with 10 litres and 10,000 ml on the page. The star line is 5.0 from 2 reviews. There is no pH and no certificate, and the coverage line is both 20 square metres and 100 litres of soil.
The top pick is Black Gold 1 litre at about £7.99. The 1 litre field and the 1,000 ml unit count agree, the origin line says United Kingdom, and the shared rating is 4.6 from 16. The 1 kg weight still does not scale to the larger Black Gold listings. The best value is EarthCraft 40 litres at about £33.98, about 85 pence per stated litre, where the family weight scales at about 105 g per litre. Dust and torn-bag comments stay in the score. McMillan’s 5.0 from 2 stays below both because of the few-review cap. None of these scores is a laboratory test.
EarthCraft Blends Bio Char Soil Improver for Plants (40 Litre)
Lowest price per stated litre among packs whose weight scales in the family, about 85 pence at about £33.98.
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 sources from the research digest, used for this page in October 2026. Prices, stars and review counts are from the eight amazon.co.uk listings in this set, captured for the 19 October 2026 scoring pass. No kept bag shows an EBC class, a Soil Association number, a pH or an NPK. RPS 366 is an England position for waste-code biochar, not a household rule for Scotland, Wales or Northern Ireland.
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.
