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A bit of a whimsical question, but I'm curious nonetheless.

Phosphoric acid (E338) - the stuff used to make coca cola tart/sour and useable as a cleaner is also used commercially to make soil more acidic for growing nightshades and curcubits.

This leads me to wonder how bad using would coca cola be to poar on a plant (for example to lower PH, or because you spilled some by mistake)?

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Fertilizer is commonly rated with an NPK ratio. The P stands for phosphorus (technically, P2O5), and it is the amount (percent by weight) of the fertilizer. So in a bag of fertilizer that is rated 4-10-6, the amount of P2O5 is 10% w/w.

The amount of phosphoric acid (H3PO4) in coke (original = 0.089%) (zero = 0.147%), and (vanilla = 0.147%). Source.

Pound for pound, H3PO4 has less phosphorus than P2O5... and since sodas like coke have a relatively minute amount of phosphoric acid, the calculations (comparing it with fertilizer) are beyond trivial. Coke/soda is nothing like a fertilizer.

The amount of carbon dioxide is about 2.2g per 355ml soda (source). As we all know, plants consume carbon dioxide; so for what it's worth, compared with humans, that's about 48.6 breaths' worth of CO2.

Calculated from 2.3lbs CO2/day (source) and 23,040 breaths per day (source)...

2.3 lb = 1043.1g

2.2g x (23,040/1043.1) = 48.6 breaths

However, soda also contain a fair amount of sugar (about 10% w/w) (source) so pouring it on a plant will likely incite bacterial and fungal growth (which would not be very healthy).

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  • To be fair, the carbonic acid could react with some soil minerals bringing the PH slightly lower immediately after application. Sugars would likely be secondarily involved in lactic or acetic fermentation as well. I wouldn't pour it on living plant material though.
    – user10810
    Commented Jul 26, 2016 at 4:14
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    @jbcreix Actually, the pH of soda is about 3, completely from the phosphoric acid. This is so far below the pKa of carbonic acid that it would actually behave more like a base or buffer than an acid, compared with phosphoric acid. The pKa is about 6... which means 2.2g H2CO3 is about 1000 times less acidic than the 0.316g of H3PO4 in a coke. And I imagine that if you poured it on the ground all of the CO2 (from H2CO3) will have evolved within a few minutes. But as the sugars oxidize (rapidly- like within 48 hours), yes... acetic acid and lactic acid buildup would also be bad for the plant.
    – Ben Welborn
    Commented Jul 26, 2016 at 12:29

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