Charcoal for Terrariums

Charcoal in terrariums is optional, but definitely recommended. It is typically layered under the soil in closed-top terrariums. This helps with humidity and any funky smells. Charcoal can have amazing benefits for plants and there are different types which have different uses. It can be hard to know which charcoal is best to use for your specific needs.

Charcoal for your terrarium should be porous and absorbent and you want it to get rid of  any impurities. Activated charcoal also known as activated carbon is best for terrariums and is available in different forms such as powders, pellets and capsules

Activated charcoal is charcoal that has been treated with oxygen to open up the tiny pores between the carbon atoms (making it extremely porous). It is treated at very high temperatures and is made by re-burning charcoal made from organic material, like hardwood or coconut shells. The results in a very fine and lightweight charcoal that is highly porous. It can absorb up to 200 times its weight and claims to absorb certain toxins and neutralize certain chemicals and funky smells (like compost for example). It is also used in outdoor soil to soak up pesticide or herbicide spills and is used for filtering drinking water.
Activated charcoal is great for removing odors and toxins from soil. When a terrarium has a closed top, the gasses the plants give off in addition to any chemicals in the soil can build up and become toxic to the plants. Bacteria can develop in the humidity and cause your closed terrarium to smell. 
I prefer to layer pea gravel, then activated charcoal, followed by sphagnum moss, then well draining potting soil, and then topped with gravel or pebbles.  This way the activated charcoal can act as a filter to pull toxins and bacteria from the soil and water and deodorizes the terrarium. Using activated charcoal at the base of your terrarium or plant pot can help prevent overwatering, while keeping pests away and minimizing the chances of fungal and bacterial growth.
Activated charcoal is great for plants growing in terrariums as it helps absorb extra water in plants and traps carbon-based impurities from gases and liquids. Basically, the main use of activated charcoal is to keep the standing water “sweet” … meaning not smelly, stinky, or rotten.
Horticultural charcoal is good for plants that prefer moist environments, such as ferns or orchids. It is a lightweight material that may improve poor soil by improving drainage and increasing the soil’s moisture-retaining capabilities. Horticultural charcoal does not absorb water as well as activated charcoal as it does not have the spongy air pockets. It still has excellent benefits for the soil and helps to keep the necessary nutrients in the soil.  It helps by getting rid of stagnant water while increasing oxygen levels and the presence of beneficial microbes. Both activated charcoal and horticultural charcoal work to protect the soil and roots of a plant from fungus and bacteria, which can lead to the plant rotting. Although I have seen horticulture charcoal recommended for terrariums, it is not binding and really serves very little benefit for terrariums.
Aquarium charcoal is obviously ideal for an aquarium that contains forms of plant life. This helps remove organic and inorganic materials that could be negatively impacting the quality of the tank water, by absorbing pollutants and acting as a filter.
Grilling charcoal, BBQ charcoal, or charcoal briquettes are NOT recommended for plants as they are not as porous and even worse can end up increasing the ph levels of the soil. They contain contaminants that can be harmful to plants and unfortunately, they just do not have the same function as activated charcoal or horticulture charcoal.
Horticulture charcoal has many great qualities but, unlike activated charcoal, it does not have spongy air pockets, so it lacks the ability to absorb odors or toxins. Horticultural charcoal also does not absorb water as well as activated charcoal so best to use activated for Terrariums. 
You can find them at any aquarium or fish store, just make sure it’s not some mixed-media filter charcoal. You only need charcoal if you plan on keeping an enclosed terrarium, though, and a lot of people will say it’s not even necessary.
I tried a few different brands and really liked this one found this here.
Charcoal for Terrariums
Charcoal for Terrariums

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