Charcoal sounds like one product until you try to buy it. Activated charcoal, horticultural charcoal, potting charcoal, biochar, aquarium charcoal, lump charcoal: related, but not interchangeable. For plant growing, the comparison that matters is activated charcoal vs horticultural charcoal.
And the stakes are real. Plenty of gardeners read that charcoal keeps a terrarium fresh, grab whatever charcoal is closest, and end up dusting their mix with filtration powder, or worse, crumbling in barbecue briquettes held together with binders and fire starter. The first makes a mix dusty and dense. The second feeds your plants chemicals they never asked for.
The short answer: activated charcoal is processed for very high surface area and belongs in filters and some terrarium layers. Horticultural charcoal, usually sold as potting charcoal, is a chunkier charcoal that improves the structure and freshness of growing mixes. If you are mixing soil, you almost always want the second one.
What Is Activated Charcoal?
Activated charcoal has been treated with heat or steam to open millions of microscopic pores. That gives it an enormous internal surface area, which is why it sits inside water filters and aquarium cartridges.
The key word is adsorption, not absorption: compounds bind to its surface. In a small closed system like a sealed terrarium, that can help manage stale conditions. It does not make activated charcoal a fix for every soil problem, and as a main potting ingredient it is usually too fine, too dusty and too expensive.
What Is Horticultural Charcoal?
Horticultural charcoal, often sold as potting charcoal, is charcoal prepared for growing media: clean, untreated and sized for pots (ours is graded at 2 to 5 mm). It keeps a mix open, holds some moisture and nutrients on its surface, and helps slow the sour, stale conditions that develop in dense or slow-drying mixes.
It is especially at home in orchid mixes, aroid mixes and terrariums, anywhere you want a stable, airy, carbon-rich component. For a deeper look at its benefits and uses, see our guide to charcoal for plants.
The Main Difference
| Feature | Activated charcoal | Horticultural / potting charcoal |
|---|---|---|
| How it is made | Processed for maximum surface area and adsorption. | Prepared as a growing media ingredient, in chunkier pieces. |
| Texture | Often fine, granular or powdered. | Chunky (around 2-5 mm), easy to blend. |
| Best use | Filters, thin terrarium layers, odour control. | Orchid, aroid and terrarium mixes, chunky blends. |
| Main benefit | Binds compounds to its surface. | Structure, air space and freshness in the mix. |
Same origin, different jobs. The question is never "is charcoal good for plants?", it is "which charcoal, doing what?"
How Much Charcoal Should You Use?
Less than you think. For orchid and aroid mixes, around 5 to 10 per cent. Terrarium substrates, a thin layer or 5 to 10 per cent mixed through. General potting mixes, about 5 per cent if you use it at all. Charcoal is a helper, not a base: too much makes a mix coarse, dry and needlessly expensive.
It pulls its weight best alongside the right partners. With orchid bark it adds structure and keeps the mix fresh; with pumice or perlite it supports drainage and air space; with coco chips it offsets the heavy, wet feel.
Can't I Just Crush Up Barbecue Charcoal?
This is the shortcut that costs the most.
Briquettes and heat beads are not just charcoal: they are pressed with binders, and many include fire-starting accelerants and mineral additives. None of that belongs near roots. Plain hardwood lump charcoal is closer, and if it is genuinely untreated it can be crushed and used, but you are guessing about what is in it, and the dust and inconsistent sizes work against you.
A proper potting charcoal removes the guesswork: untreated, washed of dust and already sized for growing media. The few dollars saved on barbecue charcoal buy you unknown additives and a mix full of powder.
Two more mistakes worth avoiding
Charcoal will not rescue a plant sitting in a dense, waterlogged mix; fix the structure first. And do not let charcoal creep past a supporting role: a little improves the mix, a lot replaces ingredients that were doing useful work.
Which One Should You Choose?
Choose activated charcoal for filtration-style jobs: a thin layer in a sealed terrarium, odour control in a closed system. Choose horticultural potting charcoal for everything you would actually call gardening: orchid mixes, aroid blends, open terrariums and chunky indoor mixes. Get the right one and it works quietly for years: mixes stay fresher, more open, and easier to grow in.
Next step: See how charcoal fits a complete mix in our charcoal for plants guide →