Horticultural Charcoal (Inactive Carbon)

Horticultural charcoal is a good drainage layer additive for those looking for a cheaper alternative to other types of charcoal. It’s more natural and has its share of benefits making it suitable for various types of vivariums. This article will serve as a guide to horticultural charcoal and help you better understand its functional use in aquariums as well as terrariums.

Quick Stats:

Technical Name: Horticultural Charcoal

Common Names: Inactive Carbon (Granular, Extruded, Bead, Powder)

Origin: Pyrolyzed Wood

Size: Up to 25mm

Color: Black

PH Impact: Alkaline

Elemental Type: Sedimentary Rock (Carbon)

What Is Horticultural Charcoal?

Horticultural Charcoal is an unprocessed form of carbon that is made from Pyrolyzed organic material. The resulting byproduct has been found to be very beneficial in the gardening industry as well as the vivarium hobby. Hardwoods are often thought to be the best source ingredient to make horticultural charcoal for the specific use of soil amendment. This type of charcoal can help retain water, beneficial nutrients, and oxygen in various types of substrates.

Horticultural Charcoal For Terrariums Guide

Horticultural Charcoal Facts

Horticultural charcoal is very similar to activated carbon in the way it is produced. The notable difference with the two is horticultural charcoal is heated at a much lower temperature and unprocessed. This makes activated carbon more porous and better as a filtration media. Inactive carbon is still useful as a drainage media and can typically retain more oxygen. Furthermore, the two charcoals are also usually produced from different source materials.


Horticultural charcoal in its crushed granular form resembles the burned wood chips it derives from. Pieces will vary in size but typically won’t be larger than about 25 mm in length. The color of charcoal will also range between black and dark gray depending on the amount of ash contained within the pile. The highly porous surface gives inactive carbon a soft chalk-like feel when touched. The typical density of this charcoal will range between 2.0 to 2.1 g/cm³.

A closer look at horticultural charcoal under a microscope will reveal strata lines and moderately porous texture. The strenuous array of holes scattered throughout the string-like appearance of its microfibers allow optimal surface space. This amount of porosity permits horticultural charcoal to trap and bind to many types of microelements much like activated carbon.


Horticultural charcoal can be derived from many types of material. Some of the more common mediums used to make this charcoal include peat, wood, coconut, and coal. The best kind of material used to make horticultural charcoal in the gardening hobby is hardwoods. This type of wood is usually taken from scrap material and inexpensive to convert at lower temperatures.

Environmental Influence

Horticultural carbon can have an impact on water parameters as well as soil depending on the size of the enclosure and how much of the material is being used. Even though the wood typically used to make this type of charcoal will have acidic PH levels, it is the ash content contained in the charcoal that is relatively high in PH. Depending on the source horticultural charcoal is made from, ash can make up 2% to 10% of the overall byproduct.

Vivarium Type

Horticultural charcoal can be beneficial in a number of vivariums. It is best used as a soil additive within the drainage layer to increase surface space for microbes to accumulate on. This kind of charcoal is usually used in terrariums and other types of dryer biotypes but is also used by experienced hobbyists in aquatic setups as well. Here is a recommended list of vivarium types active carbon is commonly used in:

Paludariums – Half aquatic/ half terrain-based enclosure.

Ripariums – Mostly aquatic-based enclosure with some terrain features present.

Terrariums – Fully terrain-based enclosure with little to no aquatic features.

Aquariums – Fully aquatic-based enclosure with no terrain features.

Vivarium Usage

Horticultural charcoal has a very specific use in vivariums. Even though it is a type of substrate, its main purpose is to provide aeration to soil and help retain moisture. It should never be used as a standalone substrate unless the intention is just to keep microfauna like springtails. Furthermore, inactive carbon is better equipped for use in systems it can be fully submerged within water. The type of enclosure it is being used in will better determine how it should be used.

In terrariums, it is common to see many hobbyists place a small amount of horticultural charcoal between the drainage layer and the artillery layer substrates. Even though many would assume it is to aid in filtering out unwanted toxins throughout the life of the enclosure, they would be wrong. Horticultural charcoal doesn’t have the same capability of absorption as other charcoals. The main goal here is to create more surface space for beneficial bacteria to accumulate.

In aquatic setups like aquariums, horticultural charcoal can reach its full potential when paired with filtering media. When placed in an area where water can continually pass through the media, this charcoal will harbor healthy bacteria that will break down toxins. In addition, it may keep the water clear and free of odor for a period of time. Due to its shortlived absorption capabilities, I would recommend using activated carbon instead of any type of filtration.


Horticultural charcoal is typically sold in the gardening industry as a soil additive. It is an excellent byproduct to help retain oxygen in substrates. The small number of nutrients it can absorb will leech back out around plants over time aiding in nourishment. In addition, it can make a good source of media for healthy bacteria and other microorganisms to accumulate.


On the contrary, horticultural charcoal does come with its flaws. The biggest drawback with using this filter media is its lack of absorption capacity. Even though its porous texture can retain some toxicity, it is generally not known as a filtration product. In addition, it can contain a large enough percentage of ash content to cause soil and water parameters to rise to unwanted degrees. This can be very counterproductive for acidic thriving plants and inhabitants.

Buy Horticultural Charcoal

Even though most companies produce inactive carbon in a similar manner, not all brands exhibit the same quality. Regardless of the company, when considering a product for purchase always do a proper inspection and buy horticultural charcoal brand new. The product should be well sealed and dry. Click the image below to find out more about the current price and other relative info:

Horticultural Charcoal Preparation & Usage

Preparing horticultural charcoal for a vivarium is relatively simple. A light rinse with RO water can be done to clear out any dust or tiny fragments. Avoid using tap water as the chemicals contained in that water will be absorbed into the charcoal. Once rinsed, inactive carbon should be used right away. Keep in mind, it is continually filtering the air it makes contact with. So once the container is opened, the media will become useless within a month’s time.

How To Use Horticultural Charcoal

If horticultural charcoal is going to be used in an aquarium, it should be added directly to the filter after the mechanical filtration. Placing the material before any type of mechanical filtration will result in tank debris absorption and make the media expire at a much faster rate. As far as its use in terrariums, this charcoal shouldn’t need any type of preparation and can be added onto the drainage layer beneath the main substrate.

How To Make Horticultural Charcoal

Horticultural charcoal is made in a very similar format to active carbon. The process is done by physical activation but at lower temperatures. Ideally, this charcoal is heated up with low amounts of oxygen to avoid low amounts of ash produced. If one wanted to make this type of charcoal, they would dig a hole about three to four feet deep and burn wood debris until smoke is no longer produced. The leftover black substances are then harvested from the hole and filtered out from the ash.

Horticultural Charcoal Alternatives

When it comes to drainage media, Horticultural Charcoal can be seen as a considerable addition. But that doesn’t mean there aren’t alternatives one could consider. In fact, there are many other products out there that will work just as well without buffering soil PH. If the intent is to use inactive carbon as a source of surface space for bacteria than consider gravel-size vivarium rocks that will have no PH impact on the enclosure. Furthermore, for other drainage media options consider some of the posts below:

Expanded Clay Pebbles | Hydroton, LECA, Etc.
Activated Carbon For Aquariums & Terrariums
Tree Fern Fiber (Peat & Panel) Substrate Guide


In summary, horticultural charcoal can be great for vivariums under the right conditions. It’s a great addition to the drainage layer of a terrarium for those looking to increase aeration and water retention in substrates. In addition, it can be a really good source of substrate for springtails and other microbes to live on. Furthermore, I’d recommend not using this type of charcoal in aquariums since there are far better alternatives you could consider for the same reason. What are your thoughts on this kind of inactive charcoal in vivariums?