# Charcoal



## JAB (Feb 21, 2017)

I see charcoal in many potting mix recipes and was wondering what the general consensus is on such an additive? Needed? Waste of money? 
There seems to be different opinions as to what it offers as well... moisture retention? Aeration to roots? 

Thanks
Jake


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## gonewild (Feb 21, 2017)

For me plants grow better with charcoal than without. I don't know what the charcoal actually adds but it adds positive.


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## Linus_Cello (Feb 21, 2017)

My understanding is that it's a waste of money. First, you need research grade charcoal for it to be effective (expensive to begin with). Second, supposedly the charcoal loses its effectiveness quickly, so you would have to replace it in a few weeks/months.


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## gonewild (Feb 21, 2017)

No offense but you don't need research grade charcoal.
But you do need natural vegetable charcoal (not BBQ briquets made with additives or from petroleum or coal). Use natural wood charcoal.

It may be a waste of money if you pay too much for it. However regardless of cost plants respond well to it and there is zero negative reaction.


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## NYEric (Feb 21, 2017)

I use charcoal in mixes, I believe it absorbs bad chemicals.


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## Ray (Feb 21, 2017)

Expanding upon Lance's comments, you want _hardwood_ charcoal, not pine charcoal, which is what most barbecue briquettes are made from.

On a positive note, the stuff doesn't decompose. On the negative side, the fine porosity and the small amount of activation, as opposed to essentially 100% activation of lab grade stuff, "grabs" and holds salts and waste products, not allowing them to be easily flushed from the medium.


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## gonewild (Feb 21, 2017)

Ray said:


> On a positive note, the stuff doesn't decompose. On the negative side, the fine porosity and the small amount of activation, as opposed to essentially 100% activation of lab grade stuff, "grabs" and holds salts and waste products, not allowing them to be easily flushed from the medium.



Ray does that mean the non activated charcoal filters out waste better than activated? (I'm not sure I'm reading right).

That brings up a question of what "waste" the charcoal grabs. Is there waste? other than excess fertilizer, assuming we apply only nutrients when we water and fertilize. I don't see an issue with the charcoal holding nutrients in the media rather than leaching them out and would actually consider it a plus. I'm interested to hear your opinion on this.

I have never used activated charcoal in the mix so don't know what difference it would make. I would assume activated charcoal would be a waste of money considering it's high cost.


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## PaphMadMan (Feb 21, 2017)

Charcoal is a relatively light weight material that does not break down, and holds water while maintaining aeration. In other words, it is a nearly ideal component of orchid media. 

Whatever other benefit people imagine is greatly over-estimated or fairly short term in action. Whatever detriments are claimed are no worse than other media choices overall. And like any media choice it will influence appropriate water and fertilizer practices. 

There is good evidence that in soil environments it is beneficial for long term fertility and good structure of soil, but orchid pots aren't really soil environments, and aren't long term.


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## gonewild (Feb 21, 2017)

Here is a PDF about benefits of charcoal for plants:

http://www.eprida.com/eacu/PDF Files/MOgawa.pdf


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## JAB (Feb 22, 2017)

Thanks Lance. Good find. 
Seems to have the same positives as perlite with the possibility of absorbing excess salt. 

Good info guys, thanks.


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## Ozpaph (Feb 22, 2017)

I like charcoal and its cheaper than bark, so a good 'expander'.


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## Ray (Feb 22, 2017)

Lance, activated charcoal will always absorb better. "Activation," in this case, involves dead-burning it in an oxygen-deficient atmosphere. The result is ultra-ultra fine porosity and high surface area so it may adsorb more stuff. Horticultural charcoal is a "junior" version, with coarser porosity and less surface area.

Once activates charcoal "grabs" something, it never lets go, and when it is "full," it simply stops being active. The same cannot be said for horticultural charcoal, which can rerelease absorbed stuff, much as a sponge soaked in food coloring will release it into water if submerged.

What are the trapped wastes? I don't know. I have read that the compensatory "wastes" upon fertilizer absorption is nothing more than OH- and H3O+, but if you've ever smelled the water in the S/H reservoir, or a plant in water culture, it must be more than that!


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## JAB (Feb 22, 2017)

Good info Ray. Thank you for learning us good!


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## Bjorn (Feb 23, 2017)

I have always considered charcoal as a potential source of problems. Once it is loaded with whatever it absorbs and starts to release it, trouble is approaching. Then it is time to repot. Without charcoal, no accumulation and less urgent with repotting.
If you do a search on charcoal you'll find lots of comments.


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## PaphMadMan (Feb 23, 2017)

As Ray pointed out, charcoal that isn't the activated type doesn't absorb in the same way, so doesn't have the same possibility to accumulate "whatever" and release it later. In fact, probably no more so than many other media components. Ideally, horticultural charcoal is exactly the opposite, being far less pure carbon with more organic characteristics of the original wood or other biomass remaining and much coarser porosity. Whatever comments may be out there, you will also find much solid research on the benefits of charcoal in horticultural uses.


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## gonewild (Feb 23, 2017)

If charcoal causes problems after time It would be a good piece of knowledge to know what the charcoal becomes loaded with that in time does damage to the plants. 

I would assume if charcoal is mixed with other organic media, like bark, that the bark would decompose before the charcoal became a problem. And if the charcoal becomes loaded with harmful elements in less time then the water being used is really bad. If the water/fertilizer contains bad stuff it should be filtered before use, or filtered in the substrate by charcoal??

Here is *a case study of charcoal added to substrate* of ornamental potted plants.
Scroll down to the study done using charcoal.
2.3. Conifers wood biochar as peat reduced-growing substrate for containerized ornamental plants


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## Stone (Feb 23, 2017)

Bjorn said:


> I have always considered charcoal as a potential source of problems. Once it is loaded with whatever it absorbs and starts to release it, trouble is approaching. Then it is time to repot. Without charcoal, no accumulation and less urgent with repotting.
> If you do a search on charcoal you'll find lots of comments.



I question this Bjorn. What kind of ''accumulation'' are you talking about? I don't know (can't find) the difference in the CHC between bark and charcoal but the point is that char does have a CEC. (activated char only higher) This means it will attract base cations like Ca, Mg, K, Na. It does not ''hold on'' to them and release them after some time for no apparent reason. The cations are exchanged for others as they get used by the plant or the concentration in the medium water changes. This is a good thing. It means we can reduce the amount of nutrients given to a plant and still get the same results.

We often see roots clinging to pieces of charcoal which means that it has the physical properties which plant roots find attractive and because of the CEC it also means that these are sites of nutrient absorption. As opposed to for example polystyrene. Roots also adhere to bark but because the surface of bark is slowly broken down by microbes, the connection with roots is more temporary and to my mind more of a source of problems than charcoal.

Once the char becomes loaded with cations, it is not possible that it will continue to accumulate more and more. It is limited to the amount of negatively charged sites. Those there are simply exchanged for others when the environment around them changes. Peat has a very high CEC (much higher than char or bark) yet there is no talk of peat having a problem with accumulation. If we are talking about plant ''wastes'' like dead cells, gasses or whatever, these materials are not held in charcoal any more than any other porous medium and flushing with water will remove it from the substrate.

I really don't see any problems with using charcoal but I do believe it has beneficial properties and I think this ''accumulation of salts'' issue being been as a problem does not appear to have any basis in fact.
In theory, we should be able to grow a plant in pure char for an indefinite period if managed correctly. 

The so called ''sweetening'' effect of char due to it's high pH is I think over emphasized and probably only temporary.
There is a commercial orchid nursery just down the road from me. They use a 33/33/33 mix of char, bark and perlite (or lava) and would not dream of changing the mix.

I've been using charcoal for many years and I can't say I've ever noticed a problem. What is probably most important is using a good clean product which has not been contaminated with some toxic substance.


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## Bjorn (Feb 24, 2017)

Mike, its just my own perception, but then I do not have much experience using it either Finding horticultural grades is hard up here in my corner of the world
I am not familiar with common procedure to measure CEC, but I doubt that bark etc has as high adsorption potential as charcoal, any grade. Just because of the diferences in surface area. Perhaps the adsorbed species on charcoal adheres so strongly that the CEC measurement disregard them, after all CEC should be reversible?
The sweetening effect of charcoal can be attributed to its content of calcium, phosphorous and potassium as well as other nutrients. Particularly if bark is charred, it may contain some nutrients. Why roots cling to substrates, well, that is probably because they want to anchor or to get access to something. 
Generally speaking, in my mind, a substate should chemically and physically mimic the conditions the different species see in nature. In nature most paphs see moss and stone, perhaps a bit of sand and bark( probably not much thats right) but charcoal, plastic etc is rarer.
On the other hand, if people are happy with a given mix, why not continue, there is not only one answer to this question.......


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## myxodex (Feb 24, 2017)

I don't think that the CEC of charcoal is particularly significant, at least not when compared to something like diatomite which has quite a high CEC. Activated charcoal does bind certain types of organic molecules by a different type of binding activity (van der Waal's forces) which is why it can be quite efficient at removing some organic dyes, pesticides and herbicides from solution. It is also used in orchid propagation medium to absorb toxic compounds released by stressed plants but as a side effect it also reduces the amount of added auxin in these media. It is also why when medicating fish in an aquarium with certain drugs you have to remove any activated charcoal from the filter system beforehand. Some leaf-eating monkeys seek out and eat charcoal (charred wood from forest fires) as an antidote for the toxins in their diets. The primary use of charcoal as an absorbent in general is in it's ability to bind organic compounds and not for it's CEC activity which is pretty minor.

The link posted by Gonewild above indicates that it helps when introducing mychorrhiza in soil systems. It could be that it provides temporary protection by neutralising antibiotics or other growth inhibitors produced by the endogenous soil microbes and so helps the introduced species to get a foothold. We should not forget that there is a considerable amount of microbial biochemical warfare going on in soil systems, it is after all the driving force behind the evolution of antibiotics.

Charcoal can bind denatured proteins, oligopeptides and other organic compounds and together with the high surface area it makes a good place for bacteria to grow. Some drinking water filters that contain activated charcoal to remove pesticides and herbicides etc. from water also have silver added (in some form ?) to inhibit bacterial build up. At the interior of horticultural grade pieces it is possible that anaerobic conditions might occur due to bacterial activity and it is concievable that inhibitory substances could be released in time and that this could have a negative impact on other more beneficial microbes and also the plant ... but I don't know if anyone has studied or measured this ?

I don't use horticultural charcoal in my regular potting mixes, but I do add granular activated charcoal to seedling mix when deflasking. I'm talking about the stuff sold for aquarium filters with approx 5 mm average diameter. I can't say that it does anything, because I've always added it following a recommendation from another grower who swears by it for use in deflasking mix.


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## JAB (Feb 24, 2017)

Great post Mike. 

Well in the end if charcoal is good enough for Terry Root to put into his mix, its good enough for me.


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## naoki (Feb 24, 2017)

I've been using left over charcoal from wood stove (birch is the wood). Sifting the ash is kind of messy, though. pH might not be so important for epiphytes, but I try to add it for plants known from more alkaline soil. I haven't compared the pour-through to see if it really makes difference, though.

I also wonder if charcoal contains some residual Karrikinolide (Kar-1), and whether it may have a positive effect. That is a relatively recently found bioactive component of smoke water (people use it for germination of Australian plants).


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## Stone (Feb 25, 2017)

naoki said:


> I've been using left over charcoal from wood stove (birch is the wood). Sifting the ash is kind of messy, though. pH might not be so important for epiphytes, but I try to add it for plants known from more alkaline soil. I haven't compared the pour-through to see if it really makes difference, though.
> 
> I also wonder if charcoal contains some residual Karrikinolide (Kar-1), and whether it may have a positive effect. That is a relatively recently found bioactive component of smoke water (people use it for germination of Australian plants).



I smoked some native seed just last week. (over smoking embers that is not in a pipe!)


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## myxodex (Feb 25, 2017)

naoki said:


> I've been using left over charcoal from wood stove (birch is the wood). Sifting the ash is kind of messy, though. pH might not be so important for epiphytes, but I try to add it for plants known from more alkaline soil. I haven't compared the pour-through to see if it really makes difference, though.
> 
> I also wonder if charcoal contains some residual Karrikinolide (Kar-1), and whether it may have a positive effect. That is a relatively recently found bioactive component of smoke water (people use it for germination of Australian plants).



Thanks for that, it's very interesting. There is a report here ( http://www.sciencedirect.com/science/article/pii/S0254629915003397 ), suggesting that it's action might be similar to gibberellic acid in some respects. 

There is a curious coincidence about this paper and your question about karrikinolide in charcoal. I started reading up about activated charcoal for use in orchid propagation media and whether I should add it or not. I came across a review about the use of activated charcoal (AC) in plant tissue culture from the same lab as the above link (J van Staden; https://link.springer.com/article/10.1023/A:1006119015972 ). Also from the same lab a paper on the interaction between auxins and AC, indicating a greater auxin response in the presence of AC than without it. (http://www.sciencedirect.com/science/article/pii/S0254629915303975 ). This result conflicts with a study that showed that AC reduces the available "free auxin" when added to TC media from another lab (will have to find the link). Yet another lab indicating that AC can induce rooting in protocorms in the absence of added auxin, and that AC could be a substitute for auxin addition in poorer countries. It's quite possible, even likely, that there are a bunch of active compounds present in AC. What I remember from this reading in general was a fair amount of conflicting results. It could be that the source of the AC is important. Although the most commonly touted hypothesis that AC absorbs toxic compounds released by stressed plants seems reasonable, I didn't get the feeling that it was really nailed down by direct evidence and so the positive effects of AC in plant tissue culture does seem to remain without a definitive mechanism of action.

OT,... but personally for me, this brings up memories of hot days and struggling to stay awake in Botany 1 lectures as an undergrad student at the University of KwaZulu-Natal where both the late Joyce Stewart (Angraecoid Orchids book) and J. van Staden were my lecturers. Botany was not my favourite subject back then ... if a life form didn't move about it wasn't interesting for me ... seems I've changed a bit over the decades.


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## Gilda (Feb 25, 2017)

gonewild said:


> For me plants grow better with charcoal than without. I don't know what the charcoal actually adds but it adds positive.[/QUOT
> 
> Mine do also I've noticed.


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## Ozpaph (Feb 26, 2017)

Some of the 'older' Aussies might remember Mt Tamborine orchids. They grew cattleyas in 100% charcoal for many years - quite successfully.


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## RodN (Mar 12, 2017)

Ozpaph said:


> Some of the 'older' Aussies might remember Mt Tamborine orchids. They grew cattleyas in 100% charcoal for many years - quite successfully.



So did Ron Lin of Sunnybank Orchids in Sydney, along with most of his miscellaneous genera.

I use it to space the bark and to aid in drainage. It is light, it is inert (perhaps) and it has worked for me for many years. I do repot my slippers annually so there is probably not enough time for any problems to show.

However I grow other genera in a similar mix and leave them in the pots for years without a problem.

I do not know but I suspect the benefits derived from having charcoal in your mix are all physical. It is a great spacer.


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