Is Miracle-Gro Potting Mix Dangerous? (2024)

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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Is Miracle-Gro Potting Mix Dangerous? (2024)

FAQs

Is Miracle-Gro potting mix safe? ›

Chemicals found in synthetic fertilizers are known to affect human lungs, urinary systems, and more. The primary ingredients in synthetic fertilizers like Miracle-Gro are urea nitrogen and ammonium sulfate. When exposed to the air, these compounds can create a greenhouse gas that damages human lungs.

What are the problems with Miracle Grow potting soil? ›

Among most common negative effects are : sunlight is prevented from reaching other plants and creatures. oxygen is depleted from the water (all those tiny plants need to breathe, too)

What chemicals are in Miracle Grow potting soil? ›

Miracle-Grow Potting Mixes contain a blend of sphagnum peat moss, aged bark fines, perlite, plant food, and a wetting agent. Miracle-Grow Moisture Control Potting Mix also contains coir (coconut husks) to help protect against over and under watering.

What happens if you put too much Miracle-Gro on plants? ›

Too much fertilizer can potentially cause a chemical burn on the roots of your plant. In severe cases, it can also cause the whole plant to wilt and die. This is something that you might see happen within a few days of fertilizing. You'll need to act quickly if your plant has been overfertilized.

What is one reason not to use Miracle-Gro? ›

Miracle-Gro is a synthetic fertilizer that contains ammonium phosphate and several other chemicals that can be toxic to your soil and plants. It is prohibited from use in certified-organic farming. Usually these fertilizers are also highly soluble, so they leach away and pollute our water systems, too.

Are there bugs in Miracle Grow potting soil? ›

Miracle Grow does have fungus gnats.

What is the difference between Miracle Grow potting soil and potting mix? ›

Potting mix is basically the same, regardless of brand. You'll find composted organic matter, sand and peat moss. In some of the less expensive brands, there will be bark chips, as well, which adds bulk. Miracle Gro Potting Soil has some garden soil (loam) and some fertilizer mixed in with the organic matter.

Why can't you use Miracle Gro garden soil in pots? ›

Soil taken from your yard or a garden bed is too dense to use in a pot or raised bed. Instead, for containers, you'll want to use potting mix (also called potting soil), a lightweight and fluffy alternative. For raised beds, you'll want to use a blend of potting mix and garden soil.

What is the problem with potting mix? ›

With potting mix, the main worry is legionella longbeachae. This generally causes a lung infection such as pneumonia. Symptoms can initially be fever, aches and pains, which are fairly general of illness.

What to use instead of Miracle-Gro? ›

Your neighbours could use liquid kelp or fish emulsion. They are liquid products that are diluted in water and then used to water the plants – ideal for containers. Fish emulsion has a bit of a smell when you're mixing it up, but when it is absorbed by the soil, you don't smell anything.

What is the difference between potting soil and potting mix? ›

Both potting mix and potting soil have their unique strengths—potting mix is great for providing superior drainage, while potting soil is nutrient-rich due to its composition, for instance. Here's when to use each growing medium.

Is Miracle Grow toxic to soil? ›

Copper sulfate is also a bactericide, and as such, is incredibly harmful to soil life. Anything with the Miracle-Gro label should be avoided entirely: Bagged potting soil and garden soil, 'Shake n Feed,' the blue crystals, and yes, even so-called “Organic” Miracle-Gro products should be entirely avoided.

What are the signs of overfertilizing plants? ›

Symptoms and signs of over-fertilization
  • Crust of fertilizer on soil surface.
  • Yellowing and wilting of lower leaves.
  • Browning leaf tips and margins.
  • Browned or blackened limp roots.
  • Defoliation.
  • Very slow or no growth.
  • Death of seedlings.
Jul 5, 2023

Do I need to add fertilizer to Miracle-Gro potting mix? ›

Plus it has perlite to help oxygen needed by plant roots to flow through the soil and plant food to get the growing started. Then—you guessed it—you'll need to take fertilizing into your own hands a month after planting.

Is there a difference between Miracle Grow potting mix and potting soil? ›

A bag of potting soil is heavier than a bag of potting mix. Potting mixes do not contain any soil. Potting mixes are used for container planting, especially for orchids, succulents, and cacti that need good drainage. A bag of potting mix is lighter than a bag of potting soil.

Why can't you use Miracle-Gro garden soil in pots? ›

Soil taken from your yard or a garden bed is too dense to use in a pot or raised bed. Instead, for containers, you'll want to use potting mix (also called potting soil), a lightweight and fluffy alternative. For raised beds, you'll want to use a blend of potting mix and garden soil.

Is Miracle-Gro toxic if ingested? ›

Inhalation : Exposure to decomposition products may cause a health hazard. Serious effects may be delayed following exposure. Skin contact : No known significant effects or critical hazards. Ingestion : No known significant effects or critical hazards.

What are the disadvantages of potting mix? ›

The main disadvantage of potting soils is that it can be expensive, while soil from your own garden is free. Some plants can be harmed by a potting mix intended for another type of plant. Also, some potting mixes are not suitable for organic gardening because of synthetic ingredients they contain.

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