The Pothos Rooting Myth

We’ve all heard it.

If you’re rooting cuttings in water, you should throw a cutting of Golden Pothos (Epipremnum aureum) into the same vessel, because it helps the “companion plant” root faster. If you search online – particularly on TikTok and Instagram/Facebook reels, in my experience – you can find dozens and dozens of examples of people who swear by this method, often with scientific-sounding explanations attached.

Unfortunately, every indication is that this is completely a myth. (To be fair, I should probably be calling it a “theory” from here… but I’m going to stick to “myth” to hammer home how certain I am.)

DISCLAIMER: I will acknowledge here that it’s frankly impossible to categorically prove that this is either a myth or true, currently. Many have conducted at-home “experiments” in an attempt to prove this as a (wonderfully well-intentioned!) effort to add some scientific rigor. While I love the thought process, and sometimes at-home experiments are perfectly fine, this is a situation where there are just far, far too many confounding factors to make a simple experiment pass scientific rigor. Things like total leaf surface area, lighting intensity throughout each cutting’s available surface area, temperature and oxygenation of the water, availability of necessary nutrients that happen to have been stored in each cutting when it was taken, pre-activation level of the axillary bud/node’s meristem tissue, and above all just plain ol’ dumb luck and the natural variations from plant to plant and node to node mean that you can’t grow multiple cuttings in an attempt to isolate a single causal factor.

What this means is that the only truly scientific way to prove or disprove this theory would be to measure the levels of auxins (and, to be certain, probably other phytochemicals!) in the water as/after various plants are rooting. This isn’t a simple process – there are no simple test strips! – and requires lab equipment, access, and experience that I frankly personally do not yet have… and while I’ve contacted probably about a dozen botany professors from across North America in the hopes of someone taking pity on me and performing/helping me perform this experiment to put this to rest once and for all… no bites. The divide between botany and horticulture is a huge annoyance to me, and while I’m hoping to go back to school and work towards bridging it, my hands are currently tied.

So, instead, I’m hoping to use this space to convince the world that it’s a myth in a couple less-rigorous, more-accessible ways.

WHAT THIS IS AND IS NOT

What I’m doing with this post includes::

• Pointing out inconsistencies and logical problems in the myth
• Asking questions that the myth is unable to explain
• Using what scientific studies are available to underscore the problems.

What I am not doing, claiming to do, am unable to do, and most importantly should not be expected to do:\

• Providing proof that this is a myth

The burden of proof falls on those making a claim – in this case, those asserting that golden pothos cuttings stimulate root growth in other plants. Claims presented without evidence can be dismissed without evidence – and claiming that something is a myth does not transfer the burden of proof. I’m going to show that the burden of proof has not been met, and thus the claim can be dismissed.

ESTABLISHED FACTS/BACKGROUND

Plants create chemicals (with the general term phytochemicals) for a wide range of reasons that have a similarly wide range of effects, both intended and unintended. These also have a wide range, from capsaicin as a defense against animals eating the leaves/fruits of some plants (and unintentionally making humans act the exact opposite way) to anthocyanins acting as UV protection for young leaves (and unintentionally turning those leaves red/pink/purple in some plants). The relevant phytochemicals to what we’re talking about are mostly in the group called auxins, and specifically one chemical called IAA, for indole-3-acetic acid, or honestly often simply called auxin. All plants create auxins, with IAA being by far the most commonly-found and the most important one.

Auxins have a number of different effects, depending on their location in the plant. For example, they’re one of the ways plants will bend their stems – they’ll concentrate auxin in the side of the shoot that is seeing stronger light, which contracts the cell walls of new leaves – since there’s more auxin where there’s more light, that means those cells are shorter while the “dark side” are longer, which curves the entire plant slowly towards the light. What auxin is most well-known for in the horticultural world, however, is its use as a rooting hormone – auxin is necessary for adventitious root growth from nodes/axillary buds (which are the new roots that “rooting a cutting” is intending to prompt). If you buy “rooting hormone” from the hardware store, for example, that powder’s active ingredient is largely IAA – it’s absorbed through the stem by the node, transported to the baby roots, and is used there.

That’s most of what you need to know, chemically, about what’s going on!

THE CLAIM

The most scientific-sounding versions of this claim often acknowledge and build themselves around the role of auxins in root growth – I’ll often see claims that golden pothos cuttings “release auxins into the water” to be absorbed by the companion plant, sometimes with the assertion that that species naturally produces more auxin than most other plants, so the companion plant can reap the benefits.

PROBLEMS

Right away, there are a number of problems/questions that arise.

#1: Why specifically golden pothos?

Nearly all claims that this myth is true will specify pothos (meaning Epipremnum aureum) – and practically all will say “golden pothos” specifically. Some will gloss over that (and may be using that to mean the entire species and distinguish it from the Pothos genus, which is totally fair); some actually emphasize that it’s the Golden Pothos cultivar that has this effect (and by implication say that other cultivars don’t have this effect), which makes even less sense; regardless, the fact that this is ambiguous is cause to consider how true the overall myth is. 

I’ll note that very occasionally, other plants are said to have this effect as well, such as Tradescantia species, but this is exceedingly rare and runs into the same problems elsewhere.

#2: Why would pothos have this effect?

Plants are capable of vegetative reproduction naturally, obviously, but for the vast majority of plants, it’s not their primary source of reproduction in the wild (including for Epipremnum species), since that reduces genetic diversity within the species. When they do rely on vegetative reproduction, though, for terrestrial and epiphytic plants like pothos, the usual scenario involves soil or vegetative debris – not water. This myth relies on pothos to have evolved to release “excess” auxins into water while rooting – a very “expensive” (energetically-speaking) process for not just no gain for the pothos, but potential harm to the pothos, in that the “companion plant” could then compete better for what are often limited resources. There is no evolutionary benefit to this, or even a reason for this to have potentially evolved, given how rare rooting in water would have been pre-horticulture. The only reason it works at all is that adventitious roots form in response to moisture in general.

#3: How much auxin is released into the water?

When applying rooting hormone powder, you’re generally advised not to bother during rooting cuttings in water; this is because the powder washes away and is too diluted in the water to have any effect; it needs to be kept in contact with the stem to be absorbed and effect rooting. For this myth to be true, pothos would need to be so much more effective than rooting hormone powder that it could naturally saturate the water with enough auxin to have an effect. Again, this would be extremely “expensive” for the pothos; if this were true, we would likely be seeing pothos unable to root in water due to the energy expenditure.

#4: Root growth patterns don’t indicate an excess of auxins.

Auxins aren’t a case of “more = better”, completely. There’s a limit where the addition of more auxin stops benefitting primary root growth, and instead inhibits it in favour of secondary and tertiary root growth – if pothos were producing this extreme amount of auxin, then the root growth pattern would be extremely different between pothos cuttings and other plants’ cuttings. There’s no such differentiation; pothos often grow a single long primary root before it branches, much like any other plant – regardless of if it is rooted in water or another substrate that wouldn’t be able to leach out “excess” auxins.

#5: Dicots are more susceptible to auxins than monocots.

Monocots, like pothos, are substantially less susceptible to additional auxins than dicots (such as Ficus). Despite this, monocots are nearly exclusively used as the example “companion plants”’; if this myth were true, then there would be a much more distinctive and obvious effect on dicot houseplants that would be noted. (There isn’t.)

The only possible conclusion is that this is a myth.

There is no scientific backing to this myth, and the rare time there’s an attempt at one, it still fails to answer these fairly foundational questions, and show a (completely understandable!) lack of understanding about how auxins actually work as far as root growth. If this were true, pothos would need ideal conditions to root at all, let alone help other plants root, and would show a distinct difference in root growth patterns. 

The only way to completely disprove this myth would be for a botanist to measure the water directly for auxins, and unfortunately that’s out of my reach at this time (though, hopefully, give it a couple years) –  but logically, this is a myth and can be dismissed barring any sort of scientific evidence to the contrary.