Myths of Horticultural Charcoal in Gardening

Many of us have heard of the value of horticultural charcoal in gardening, not only that charcoal could retain moisture, but also some other amazing functions such as absorbing odors, purifying water, and warding off bugs and slugs. Many of these are not true, and those vendors, who have misled their customers with exaggerated, untruthful claims in their ads, are responsible for part of this confusion.  

Myth #1: Barbecue Charcoal Works Just Fine

Not all charcoal are created equal. And horticultural charcoal cannot substitute by either barbecue charcoal or filtering charcoal. For more details, check the post: Horticultural Charcoal – Can be Substituted by Barbecue Charcoal or Filtering Charcoal?

Myth #2: Absorb Odors

Charcoal Cartoon

Horticultural Charcoal does not absorb odors, nor lower the possibility of odor-causing bacteria. In order for the charcoal to absorb the compounds responsible for the foul smell of soil that has gone bad, it needs to be activated or super-heated so to create lots of air pocket to absorb odors. But horticultural charcoal is not activated, so it lacks the ability to really absorb anything.

Of course, you can use activated charcoal in aquarium shops. Those are called activated filter carbon and can be bought in aquarium shops. But in comparison with horticulture charcoal, filter carbon is very expensive. For your reference, while $6 can buy 24 oz of horticulture charcoal, it can buy only 7 oz of filter carbon.

Secondly, adding charcoal to make up ten to twenty percent of the soil volume is not going to have any odor-absorbing properties after sitting in the soil for a short while. It is like placing a small sponge into a sink full of water in hoping it will absorb all of the water.

Myth #3: Soil Enrichment

While in some reports, it is shown that charcoal can reduce the leaching of fertilizer in free draining soils, horticultural charcoal, by itself, does not enrich soil. And in order to be a good source of potash, the charcoal must first be burned. Yet, then the charcoal will lose its porosity value.

Myth #4: Purifying Soil and Water

Charcoal does not have a special purifying quality when layered into non-draining pots. In addition, it does not purify water by mixing it with soil. As mentioned earlier, horticultural charcoal is neither activated nor super heated. Hence it does not contain the necessary air pockets for optimal filtration like those carbon filtration that use activated charcoal.

Myth #5 Insects and Disease Fighter

Charcoal has been recommended as part of the treatment for the eradication of a fungal disease, Cylindrocladium, which infects Box hedges. However, horticultural charcoal per se doesn’t ward off plant diseases, parasites, insects, or slugs. In addition, it isn’t an anti-fungal agent equivalent to sulfur or copper.

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