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How to use biochar in compost, pots and beds

Updated: October 2026

The bag is in the shed, the title says biochar, and the label may not say how much to use or whether you should charge it first. You need a sequence you can follow without treating one supplier's percentage as a British Standard. Charge plain char before you rely on it, measure by volume against the rate on your own bag, mix it into the top layer or the compost, and keep dry fines off your lungs and the patio. This is that sequence. Product ranking stays on the [biochar comparison](/hub/fertiliser-soil-and-bark-mulch/biochar). A qualifying amazon.co.uk purchase can earn a commission at no extra cost to you.

The bag is in the shed, the title says biochar, and the label may not say how much to use or whether you should charge it first.

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Invigortex Black Gold Activated Biochar Soil Amendment (1 Litre)

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Invigortex Black Gold Activated Biochar Soil Amendment (1 Litre)
7.6/10about £7.99
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Invigortex EarthCraft Blends Bio Char Soil Improver for Plants (40 Litre)

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Invigortex EarthCraft Blends Bio Char Soil Improver for Plants (40 Litre)
7.1/10about £33.98
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Invigortex The Potting Pantry Activated Biochar for Plants (10 Litre)

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Invigortex The Potting Pantry Activated Biochar for Plants (10 Litre)
2.2/10about £16.95
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On this page
  1. 1.Charge it unless the bag already did
  2. 2.A percentage, not a guess in kilograms
  3. 3.Beds, compost heaps, and what not to drench
  4. 4.Dust and a split bag

Charge it unless the bag already did

Raw biochar behaves like a sponge. biochar.co.uk describes uncharged char as holding the nutrients you apply until the pores are loaded. The Potting Pantry listing says activated, and the bullets still tell you to mix the char with compost, worm castings, liquid feed or nutrient-rich water before planting. Black Gold's title also says activated, and the product data does not describe a separate charging step, so do not invent a soak time for it. Where the bag is silent, treat 5–10% by volume with compost as a rule of thumb from sellers such as biochar.co.uk, not as the dose printed on your sack. Container percentages are finished on biochar for pots.

A percentage, not a guess in kilograms

Read the rate on the bag first. If it is silent, stay near the range those UK sellers publish, and keep each number attached to its speaker. Carbon Gold tells people to use its improver at 10% by volume when potting, or about 1 kg per square metre worked into the top 20 cm. SoilFixer talks about 5% by volume and shows that 1 kg per square metre is a different percentage at 2.5 cm, 5 cm and 15 cm depth, using its own bulk assumptions. Those figures are not interchangeable with a char that weighs 105 g per litre. McMillan's own sentence must not be merged into one dose. One 10 litre bag for 100 litres of soil is 10% by volume. The same bag for 20 square metres is 0.5 litres per square metre. Quote the sentence that matches the job you are doing.
Invigortex Black Gold Activated Biochar Soil Amendment (1 Litre)

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Invigortex Black Gold Activated Biochar Soil Amendment (1 Litre)
7.6/10about £7.99
View offer

Beds, compost heaps, and what not to drench

On a bed, work the char into the top 15–20 cm if you are following Demeter's or Carbon Gold's depth language for their own products, and only at their rate for their product. Demeter describes one of its 10 litre bags on 1 square metre into the top 15 cm. That is a heavy rate compared with McMillan's 20 square metre claim. Do not average them. In both cases the char is a conditioner beside organic matter, not a substitute for it. Whether char replaces compost is biochar or compost. Do not cultivate a frozen bed just to bury a sack.

Dust and a split bag

EarthCraft reviews on amazon.co.uk describe a fine, crumbly grade, charcoal marks, a ripped bag, and a wish for chunkier pieces. That complaint is about those listings, not a fact about every brand. McMillan's form line says granules and powder, so some fines are still likely. Open a dusty bag outdoors or over a sheet, dampen the fines before you tip them, and keep dry dust out of eyes and lungs. If the sack arrives torn, photograph it and use the seller's returns route under the Consumer Rights Act 2015.

Common questions

Do I have to charge biochar before I plant?
Charge it when the bag is plain or when the listing tells you to, as The Potting Pantry bullets do, even though the title says activated. Mix with compost, worm castings, liquid feed or nutrient-rich water, then blend that through the potting mix. If a specialist bag already includes inoculant or castings, follow that label. Black Gold prints no separate step, so do not invent a soak time and call it theirs.
How much do I mix into compost?
Use the percentage on your bag. If there is none, 5–10% by volume is the band biochar.co.uk, SoilFixer and several specialist pages use, and it is a rule of thumb. Ten litres of char in 100 litres of compost is 10%, which is also one reading of McMillan's coverage line. Carbon Gold's potting line for its improver is one part to nine. Do not convert those litres into kilograms unless you know the bulk density of the char in your hand.
Can I put it in the compost bin?
Yes, as a charging route, if you spread it through the heap rather than dumping the sack in one layer. biochar.co.uk describes raw char as something the compost can inoculate. The heap still needs a normal mix of green and brown material. Char will not rot away on the same timetable as kitchen waste, which is the point of it, so it is not a browns substitute on its own.
What if the bag has no rate?
Stay near 5–10% by volume of the mix you are making, charge plain char first, and do not scale up to a tonne-per-hectare figure from England's waste guidance. A 1 litre pot trial is enough to see whether the grade is dust. McMillan's '20 square metres or 100 litres' line is two rates. Pick the one that matches a bed dressing or a compost blend, and do not use both at once.
Is a home-made kiln part of this how-to?
No. Making char from waste wood sits under operator positions such as LRWP 60 in England, with limits on tonnage, equipment and rate. It is not a weekend drum in the garden, and this site does not give build steps. Buy a finished retail improver, or speak to the regulator for your nation if the material is waste.

Related pages

Biochar buying guide

Biochar

Best biochar for a garden, by the job you are doing

Biochar for pots and houseplants, and how much to mix

Biochar vs compost and which one you actually need

Sources

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.

  1. RHS, biochar (retrieved 19 October 2026)
  2. GOV.UK, RPS 366 storing and spreading biochar (retrieved 19 October 2026)
  3. GOV.UK, LRWP 60 making biochar from waste (retrieved 19 October 2026)
  4. GOV.UK, check if your material is waste (retrieved 19 October 2026)
  5. legislation.gov.uk, PFC 3 soil improver (retrieved 19 October 2026)
  6. European Biochar Certificate (retrieved 19 October 2026)
  7. Carbon Gold soil improver (retrieved 19 October 2026)
  8. SoilFixer, biochar application rates (retrieved 19 October 2026)