Cultivating Orchids & Crafting Terrariums

Top Benefits of Adding Charcoal to Your Potting Medium

Many orchid enthusiasts add charcoal to their potting mix and swear by that recipe. Others never add charcoal and say their orchids are growing fine. Adding charcoal to the potting medium is a personal preference but there are several things you need to know before adding charcoal.

Is wood charcoal good for your orchids? Charcoal is an excellent potting medium for orchids since it eliminates odor, breaks down the buildup of bacteria, absorbs the salt residue (therefor reduces the risk of root burn) and doesn’t degrade. Providing a firm stabilizer for larger orchid root to cling, charcoal doesn’t retain moisture, and can increase the pH of the orchid medium.

In my opinion, adding charcoal has amazing benefits, and I always add charcoal to my potting mix. But don’t believe everything you hear about the miracles and wonders of using charcoal in your medium.

First let’s take a closer look at what charcoal is and then we’ll discuss what it doesn’t do.
charcoal

What is charcoal and how is it made?

Understanding the properties of charcoal will help when it comes to using it as a potting medium. First, charcoal is not the same as coal. Coal is a mineral, more specifically fossil-fuel, which took thousands of years to produce, whereas charcoal can be man-made within hours.
Over many thousands of years, debris from the overhead trees and plants fell onto the ground and later was buried under soil. By adding pressure to the mixture and keeping those conditions like that for millenniums, coal is produced. Needless to say, coal is a natural, non-renewableresource.

Charcoal, on the other hand, is the slow-burning of wood at high temperatures, (400º C or 750º F) in the absence of oxygen so it wouldn’t combust, bursting out in flames. During this process, called pyrolysis, water was eliminated, leaving behind a chuck of carbon, nitrogen and potassium.

What’s the difference between activated charcoal and hardwood charcoal?

Activated charcoal is not the same as hardwood charcoal. Many articles claim that the main difference is the porosity of the surface and the price. This isn’t quite true. Well, at least not the porosity part. The surface of the coal is the same, but when “not activated”, the pores are occupied with gases created during heating, eliminating the usable surface area.

Hardwood charcoal that comes directly out of the “oven” has an immense ultra-fine surface, filled with pores. The slow-burning process quadrupled the surface area of the initial wood. Yet during this procedure, the pores filled up with the smoke around them, because that is what charcoal does. It absorbs the nutrients, chemicals, smells, bacteria—whatever it has around it. So even though these pores are now there and the surface area is amazing, allowing roots to cling to them and love them, they have tenants: smoke.

To activate a charcoal means to rid the gas (or smoke) that built up inside the extremely porous surface during its creation, and replace it with nitrogen. Nitrogen will depart from the pores during natural gas exchanges, leaving the charcoal with a much larger surface area again.

Hardwood charcoal still works as an amazing absorbent, in whatever shape you buy it in: chunks, powder, particles, pellets, and pressed cylinders. So, don’t fret if the activated charcoal is harder to find or more expensive. Utilize the hardwood charcoal and you’ll still see the results.

Why add charcoal to the Potting Medium?

There are several reasons. First, charcoal is known for eliminating odors. Very humid climates, as the majority of orchids love, invite growth—every kind of growth—especially the types we don’t want.
charcoal on fingers - orchid potting mix
Mold and bacteria thrive in wet conditions. This infamous duo produces a unique, horrendous odor. The solution is charcoal since it slows micro-organism growth, binding toxins that are extremely important for the mold metabolism.

Aquarium builders swear by adding charcoal in their displays. In every single article I read about building aquariums, ripariums, and vivariums, the experts added charcoal for the same reasons mentioned above: (1) it reduces the smell, and (2) breaks down bacteria.

Charcoal is also used to eliminate toxins in industrial plants, before they leave to the atmosphere. Charcoal absorbs the harmful gases, decreasing the pollutants disposed into the air.

Nutrition experts also use activated charcoal in pills or tablets, used to eliminate the toxic build-up from a poor diet. The charcoal absorbs the elements that are in excess, and are eliminated, promoting a better diet plan in the beginning. If charcoal did not have such absorbing qualities and properties, then they wouldn’t be used in these different places.

If you want to read more about how activated charcoal interacts with plant tissue, this scientific article published on PubMed and written by T. Dennis Thomas on "The Role of Activated Charcoal in Plant Tissue Culture," explains that perfectly.

The second reason to add charcoal is that it absorbs salt residue of synthetic fertilizers. Charcoal absorbs whatever is around it (except water) and the chemicals that were introduce during watering or fertilization are no exceptions. This is an important step if your orchid has root burn.

How does charcoal aid in curing orchid root burn?

Root burn is verified when the roots will turn brown or darker than usual, almost a grayish-black. This isn’t root decay, but root burn, caused by the salt sitting on the top of the medium and brown residue on the sides of the pot. Charcoal can aid in eliminating this problem.

Orchids get their nutrients through the air and what rainfall brings to them from debris of other plants. Since orchids grown inside don’t have a tropical rain forest hoovering above them, we need to add fertilizers during the watering.

Many fertilizers contain excess chemicals and stronger substances, that is why we recommend always diluting the recommended dosage. Over time, the fertilizers will evaporate, leaving salt behind on the surface and sides of the potting medium, closer to the ventilation slits.

Having these acidic toxins close to the roots for a prolonged period of time will harm the sensitive roots. The first sign of root burn will be the white velamen (fuzzy stuff on the roots) dry up and turn brown.

Salt-build up can be reduced also by giving the orchid a proper rinse.

Let running water pour through he orchid, rinsing away any build-up that has occurred. This is harder done with medium like lava rocks, where the salt build-up likes to adhere with tenacity. But sphagnum moss, charcoal, fir bark and other mediums are easier to flush out. If you see a white, shiny build up that can sometimes sparkle when light this it, then you need to thoroughly rinse out your orchid under running water.

What does charcoal do to the pH of my orchid?

A few paragraphs back, I mentioned the salt-build up reduces the pH of the orchid medium dramatically. If not flushed properly and regularly, the orchid medium can reach an acidity of 3 or 4.

Bad quality sphagnum moss can also bring the acidity down even more.

Charcoal increases the pH, bringing the medium up to more neutral levels. This counter balance is necessary to maintain a healthy orchid.

In one research, an orchid enthusiast soaked the roots of her root-burned orchid in a water solution with a little lemon and vinegar. Although it was an interesting read, I don’t recommend this method, and neither did several people in the commentaries. Charcoal helps with increasing the pH.

Does charcoal expand the time in between repotting?

charcoal, orchid fertilizer
One finding that I could not confirm nor deny is that adding charcoal to the potting mix will increase the time that you need to replace the potting mix. A by-product of using charcoal to increase the drainage, is preventing the decay of other medium.
For example, one article stated that if using sphagnum moss alone, the potting mix will need to be traded out in 6 months due to decomposition and breakdown, compacting the residue. If adding charcoal to the potting medium, the sphagnum moss will last around a year before needing to be traded.

Another example that was used was the pine bark. Without charcoal, pine bark would last 12 months before a repot was required. When added charcoal to the mix, the pine bark lasted 2 years.

I cannot prove or disprove that charcoal increases the time in between repotting. In my research, I found only word of mouth and fables, but nothing really reliable to bet my last dollar on.

In the article "Tips for Growing Orchids in Apartments", published by Singapore's National Park's quarterly newsletter, named MyGreenSpace, they state that "The potting medium is an important factor for the orchids to get enough moisture. Traditionally, orchids are grown in charcoal and broken brick pieces, but there are several other good options. Sphagnum moss retains water well and a little can be added to charcoal or broken brick pieces to increase the humidity in the pot."  Source  Singapore Government, National Parks.

On the other hand, since I didn’t find any research to disprove these findings, they may have some validity. What was proven though, was that charcoal does improve the drainage and doesn’t decay. Both of these qualities aid in expanding the time in-between repotting.

How does charcoal improve drainage?

Another reason to add charcoal is that it is a great source for rapid elimination of water. Unlike sphagnum moss, charcoal doesn’t absorb or retain water, allowing the water to run freely around it. With too many additives that absorb water, your planting medium could become overly moist. This is not a risk when using charcoal.

Charcoal doesn’t degrade

Fir bark, sphagnum moss, and other natural resources will decay and degrade over time. Charcoal, to the most part, doesn’t. It has already done all the decaying and degrading that it’s going to do. Ok, in all honesty, it does degrade slowly, but this process will take decades.

So we’ll stand by our answer. Other materials will have to be replaced continually, usually once every year or every other year—not charcoal.

Charcoal increases soil "fertility"

To an orchid grower, this is questionable since the majority of the orchids we deal with grow on trees. Anyway, the resource here is the tropical rain forest soil, and its “nutrient-rich soil.” The myth starts here. The soil in the rain forest is actually very poor—extremely poor. All the nutrients in the rain forest come from other sources, not the soil.

Yet there is an abundant amount of charcoal in this soil, giving it the name “Terra Preta”, or Dark Earth. Some articles uphold this idea because the charcoal keeps the nutrients that have been deposited in it’s micropores, only releasing them in time. Due to our research in how charcoal is made and the properties of the soil in the rain forest, this is plausible.

This would also mean that if you use a fertilizer (as you should) to water your orchids, the charcoal will absorb these nutrients for a longer period of time than those mediums which lack charcoal. Less fertilizer will need to be used.

Another supporting idea for increased fertility is that charcoal is nothing more than a lump of carbon and a natural source of potassium...and carbon is essentially beneficial to plants.

With the air pockets that the charcoal has, there is more gas exchange inside the medium, promoting air flow and toxin removal. This can be tied into the increased fertility or promoting optimal gas exchanges, but either way, your orchid appreciates having carbon in its potting medium.
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Charcoal is a hard-enough medium to stabilize larger plants

Larger orchids can’t thrive in just sphagnum moss. Their roots need something stronger and larger to hold on to. Clinging to large chunks of charcoal provides the perfect medium (that isn’t too heavy, either) stabilizing the roots.
orchid gift
One subscriber questioned if it would be okay to plant an orchid in charcoal only. I have never done this myself, but my initial answer would be “No,”.

As always, I love a good question, and set out to find the answer. To my surprise, there are exceptions to where planting in only charcoal are recommended. If you live in an extremely humid environment, which rains almost every day, then I’d give this answer my full “Yes!”.

Charcoal doesn’t retain any of the humidity that sphagnum moss or pine bark do, causing your orchid to dry out fast. Even if you watered the orchid every day, it still can’t get the humidity from the just the charcoal.

You’d have to soak this orchid regularly.


Another exception are the orchids that do well mounted. Still, mounted orchids are crafted with a tiny bit of medium, and providing only charcoal would not allow for this extra humidity.

If you’d like to try potting in charcoal only, I’d increase the times and amount of water you provide your orchid. I’ve heard of this method done in other places, but have not tried it out myself—and have no desire to, either. I just cringe when I think how my orchids would react.

Is there a better charcoal?

I won’t get into brands here, but yes, there is. You can pick up a bag of your outside BBQ grill charcoal, if it doesn’t have additives, like a special bacon-flavored chemical. Get the cheapest one, and verify that it’s just the charcoals. Anything added to prolong the burning time, or make it light faster is not the best choice.

Bad quality charcoal is usually a softer wood used to start with, like soft pinewood. This will degrade faster than the normal, hardwood charcoal does. Do it yourself charcoal is also a bad, bad, very bad idea—remains from a fireplace—bad idea.

You can find horticulture charcoal most everywhere. So please don’t go out and do-it-yourself type thing. Trust me, your orchid will frown.
If you're looking for suggestions for Charcoal to use in your potting mix, try these brands below. The links will lead you to Amazon and they are not in order of preference.
Now that you know all about charcoal, what to look for when horticultural charcoal, and how to repot your orchid using charcoal in your potting medium, it’s time to get your hands dirty. Check out some of our tutorials on how to design a great floral design or build a terrarium with orchids.

If you'd like to read some more before trying out orchid growing, you can check out our article on using sphagnum moss as potting mix or another article on proper humidity for your orchid.


If this information was of any help, and clarified any doubts you had, please mention so in the comments. We love to interact with other orchid enthusiasts, and can share from our experiences. Share this page to a friend who has an orchid, comment, or just give up a 😊 in the comments below.

Happy cultivating!
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Amanda June Matthews at Orchideria
Hi, there! I'm Amanda Matthews.

I write all the tutorials on Orchideria so unfortunately, I can't blame anyone else for all the spelling mistakes.   :)

By profession, I'm a theologian, author, and seminary professor, yet I  spend my free time enjoying nature hikes, building terrariums, and cultivating orchids. I also love to mountain bike on trails, dance, and play with my dog, Max.

When I'm not working on the next chapter of my book or online course, I'm exploring a new campsite to venture out into nature. Pitching a tent for the weekend with my two children while I fire up a barbecue is the best way to live.

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