Is Miracle-Gro Potting Mix Dangerous?

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Miracle-gro is perfectly safe. But misunderstanding fueled by misinformation abounds —

I was so happy with the results I was getting with my “Simple Bioactive” cage designs (See: A Quick Overview of Simple Bioactive) that I completely overlooked the gathering storm of outrage from my fellow keepers! Unknowingly, I offended the closely held dogma of a number of keepers – from dart frog (especially dart frog!), to other frog, snake and lizard keepers. Almost none of the criticism was fact based. In fact so much of it was bordering on the personal and hysterical that I had to learn to reign in my response!

I wouldn’t care at all except I have found Miracle-gro potting mix to solve a number of herpetoculture problems and provide a significant boost in the quality of care we can offer our animals. So I really wanted to share the news. But my “Middle Way” (See: The Middle Way of Herpetoculture) didnt just present a new paradigm, it undermined the authority that group “experts” were enjoying at the time. It was through this process that I realized I was offending a set of dogmatic beliefs as deeply held as any sincere religious beliefs. It was a fascinating experience that brought me back to my days as a graduate student in Anthropology at the University.

The fear that this new paradigm manifested in many produced an endless stream of assertions about the danger of my methods in general, and Miracle-gro potting mix in particular. A few were sincere concerns presented by genuinely curious keepers. Most where defensive, angry, childish and down right silly. I would guess that I have probably been banned by more Facebook administrators than any other serious herpetoculturists because of these insecurities. And that is pretty sad.

So what are the concerns and what can I say to dispel them? Most are concerns about the fertilizer that commercial potting mix contains. Some mention specifically the “synthetic” or man-made fertilizers specifically.

There are concerns about the little white “perlite” things. Some mention pesticides too. Some are concerned about “chemicals” in general.

The easy answers are pesticides and perlite. In the US our Environmental Protection Agency requires any product containing any pesticide to be labeled with the exact contents and amounts. Its a federal offense to ignore this requirement. So we can be assured there are no pesticides to worry about.

Perlite is simply rock. It is inert and can not swell. It is derived from obsidian (a type of volcanic rock) that is ground up then super heated to “op” or “puff” like popcorn. If ingested, which is unlikely, it would pass just as any small rock would.

But what about the chemicals? The first thing to understand is that life on earth depends on the 3 main “nutrients” that plants must have to survive: nitrogen (for plants it would be in the form of nitrate – NO3), potassium and phosphorous. These three chemicals are the fertilizers that our potting mix contains.

When we buy fertilizer we can buy organic or synthetic. Organic fertilizers are derived from bat or bird feces, the waste from slaughter houses or even human sewage. These organic materials are slowly broken down by bacteria into their chemical components, some of which are nitrate, potassium and phosphorous. These are the exact same chemicals that are created thru man-made processes. If they were different in even the smallest way, the plants would not be able to use them. So there is no difference between the chemicals derived from man made processes and the chemicals derived from natural processes.

Imagine for a minute that you were in the hospital with a serious case of Covid. The doctor realizes you’ll need supplemental oxygen to survive. But when the nurse rolls the oxygen tanks in you refuse, stating that the chemical oxygen is man-made and not naturally derived. Sounds silly right? But that is the exact same argument many people try to make against the man-made nutrients found in Miracle-gro potting mix. Equally silly.

The second concern most often stated is that the nitrogen itself is toxic. That exposing our animals to even tiny amount of nitrogen is reckless and cruel. “I don’t intend to poison my animals even a little bit!” is what I have heard.

But this too makes no sense. Nitrogen is critically important to all life. A whopping 78% of the air we breath is nitrogen. Nitrogen is in every natural soil that is sustaining plants. And Miracle-gro potting mix has only tiny amounts anyway – 0.06% nitrogen, and even less potassium and phosphorous. Further, nitrogen moves quickly thru soils and substrates, it is decomposed by bacteria and it is taken up by plants. The tiny amounts of nitrogen in MGPM is literally gone within a few weeks of opening the bag and setting up your vivarium.

I have explained to people that I use a highly concentrated form of nitrogen called urea to feed my sweet corn. Sweet corn, unlike most plants, can handle huge amounts of nitrogen. I buy the urea in granular form and side dress the rows of corn by hand. This product is almost 1000 times as concentrated as the nitrogen in MGPM, yet it doesn’t even cause a rash on my bare hands.

I suspect the misunderstanding and fear of nitrogen comes from the fact that nitrate in aquariums is toxic at high enough concentrations, and that nitrate in drinking water can cause Infant methemoglobinemia (blue baby syndrome) in human infants. Technically, infants have a lower NADH- cytochrome b5 reductase activity (1) which reduces the oxygen carrying efficiency of their hemoglobin.

By the time human babies are 4 months old or so they have developed the gut bacteria needed to safely metabolize nitrates. It is important to note that at this time nitrate are not “a little bit toxic” – they are non-toxic. Just like the salt you put on your French fries is not a little bit toxic, even though salt in sufficient concentration would be lethal.

In aquariums nitrate is potentially lethal to any organism that breath thru gills. (Nitrate itself is not toxic and is even added to heavily planted aquariums as a needed fertilizer. High nitrate levels indicate potentially high nitrate precursors, nitrite and ammonia, both of which actually are toxic (2)) This is something anyone who has ever set up an aquarium understands well. It is not new news. Fish and tadpoles will suffer and eventually die if nitrate levels remain too high. But again this is because the nitrate interferes with the transfer of oxygen to the animal. It is not otherwise toxic.

I recently set up an aquarium I intended for some red-eye tree frog tadpoles and Dendrobates tadpoles. I used a couple inches of fresh MGPM as a substrate, covered with a 1 inch layer of aquarium gravel. All the aquarium occupants did great, eventually metamorphosing into adult frigates right on schedule. A group of fancy guppies kept in the sane tank grew and reproduced as expected. The supposedly “toxic” MGPM provided a great substrate for plant and algae growth – perfect for hungry tadpoles.

In addition to aquariums, I have raised horned frogs in MGPM. They remained burrowed down into the substrate unless they were hungry, when they would climb back to the surface to feed. Ive raised Dendrobates (dart frogs) on it, snakes, turtles, lizards – even isopods and springtails. All did great and remained healthy. I have literally dozens of herps living on and in MGPM and have had them on it for years in many cases.

Finally, when some folks who were most vocal about there misunderstanding were told I had many animals living on the substrate they claimed that the poisonous effects might not appear for years, or may not appear even until future generations were produced! Of course this is an argument that has no evidence, and hints of desperation. We could level the same charges against any product ever created for human or animal consumption. Without evidence these sort of charges cant be taken seriously.

1.) https://en.wikipedia.org/wiki/Blue_baby_syndrome

2.) https://www.tfhmagazine.com/articles/freshwater/keeping-up-with-nitrate

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Published by Joe

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