Orchid blunders: phosphoric acid, pH Down & phosphorus toxicity? A lesson/story on acidifying water

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This is a story and reflection on a somewhat catastrophic event that affected about 50% of my plant collection during the summer of 2019. This post is intended to inform you of what happened to me, provide insight to a single situation I experienced, and to help others who may be having similar problems while using the same products as me.

***Update April 22, 2020: It’s been 5 months since I’ve written this post and I want to intercept an update at the top to ensure misinformation isn’t spread by this post. Firstly, at this point, I don’t believe phosphorus or chemical toxicity directly caused what I am dealing with. I have come to the conclusion that my plants have a particularly aggressive fungal infection and I believe that the phosphoric acid issue I refer to below weakened the plants and made it easier for the fungal pathogen to infect them—the chain of events caused by the phosphoric acid may have been: calcium lockout, then calcium deficiency in the new growths, then fungal infection followed by total destruction of the roots as the pathogen moved toward the leaves and primary parts of the plant. In many books there is reference to a “microfungus” from the 80s that expressed similar symptoms to what I have here, and that same pathogen spreads easily via water. Although I never share water, I have to wonder if this is that. This fungus may also be one of the many strains of fusarium which is ever-present in our soils and outdoor ecosystems, and it simply had an opportunity to enter my stressed plants after the below phosphoric acid issue. Without a definitive way to test for any pathogen, ALL OF THIS is guess and largely conjecture, but I want to share this info so that others are prepared should they find this in their collection.

All of my non-orchids (tropicals, aroids, soursop tree, cacti, etc) have returned to normal since I stopped using the pH down product. Most of my orchids however, had to be treated with Phyton27 (a systemic fungicide) and the recovery of the worst-affected plants has been very slow – the roots and leaves have to be rebuilt (because they have lost most of the leaves and roots) and this has set them back by at least a year or more. I am not out of the woods yet and while some plants seem to be improving with each new leaf, I have lost many plants through this process.

If you have come to this blog post because you are battling a similar issue, my recommendation is this: either throw out the affected plant and cut your losses, or immediately apply a strong systemic fungicide like Phyton27, Cleary 3336F or Thymol. You may even want to cycle all three of these with a few weeks between each application; however, be sure to check labels as some systemics can react and I have not used the combination of these myself. If you go down the systemic fungicide route, beware that these chemicals are VERY TOXIC. Do not apply in your home. Do not apply near pets. Do not apply without protective gear—they can literally make you go blind. I recognize this is not an easy process for the average home grower, so again if you can…just throw the affected plant out and spare your collection. I should note, one person reported improvement of similar issues by increasing temperatures to over 28C; however, I haven’t been able to test this as this is in my home and just beware that the longer you keep an infected plant, the higher likelihood it may spread to other plants via pests, water, and fallen leaves.

Back to My Story

Photo of a group of effected phalaenopsis – with symptoms similar to fungus or viral attack

Understanding the Situation

What has symptoms like nutrient deficiency or virus or fungus, affects each plant differently, but takes months to really show up? It might be phosphorus toxicity, extreme acidity (though I doubt that it was the latter because I flush my pots often), a fungus or who knows…maybe just some toxic-ass product. What I can tell you is it for sure is, it’s not a virus (see test results near the bottom of this post).

As I said, about 50% of my collection (both orchids and houseplants) started to have problems—slow growth, halted and/or black roots, aggressive chlorotic patching on the leaves, and so on). I now believe it was a result of a bad bottle or brand of “pH Down” but I may never know. I’m posting my experience and this story in the hope that it’s valuable for anyone who may be having a similar problem.

I want to be REALLY clear: I don’t think Phosphoric Acid or pH Down are bad products – I just think the one brand that I used was toxic. Prior to this all happening, I was using pH Down by General Hydroponics and I had GREAT results for over a year. The product that caused all of this situation WAS NOT the General Hydroponics product. I believe that acidifying fertilizer water has had a very profound affect on my ability to grow plants better. This was just bad luck and it means I need to be more careful about choosing products and not assume that different brands offer the same quality.


What Happened?

It all began when I started noticing yellow chlorotic spots on one of my NOID phals. I threw the plant out concerned that it was a virus. Then another got similar spots, and I tossed that one too. I started to become worried; this was only weeks apart and in my research, all I could find with similar symptoms were viruses and a “Taiwan micro-fungus” – which apparently can wipe out a collection with ease. NEXT, one of my favourite phals (Mystic Princess), a primary hybrid with a notoriously difficult lithophytic species (Phal cochlearis), got yellow spots too. The spots progressed so quickly that within weeks the whole plant looked like the worse virus-stricken plant you’d ever seen. The roots had turned black and hard, and the leaves were getting dry and leathery. It read like Fusarium, it looked like potyvirus, and a plant that I cherished went from full bloom to binned in about 6 weeks. I tried treating with systemic fungicides; immediately with Phyton27 and I ordered 2 others to have for backup—but the fugicide didn’t work on these plants and the symptoms began showing up on other plants.

PS: again please beware, systemic fungicides and pesticides are some serious shit. They’re toxic and can be dangerous. I feared losing my collection to an aggressive micro fungus which was has been widely reported online and that appeared to have similar symptoms—so I tried to combat with the only thing people had reported working in the past.

Symptoms & Leaf Yellowing Spread Quickly

After I tossed those 3 plants I was getting anxious. I didn’t know what I was dealing with and whatever it was it was spreading. Various other phals began having similar symptoms: chlorotic spots, black roots, slowed (or halted) growth, but this time it was on seedling plants that I had deflasked the year before (and very likely to be free of viruses). It also started happening on plants in different areas of my home…but it was happening so slowly that I was having a hard time connecting the dots because the symptoms were inconsistent. Not every plant got yellow spots. Not every plant had black roots. But broadly, something was gradually slowing my plants down.

Removing Variables – Pests might be the cause

The problem was…I had thrips, mealybugs, and some plants had the dreaded false “red” spider mite. For the first time ever, I understood how dangerous pest insects could be on a collection if they shared viruses or pathogens between plants so easily. I thought I had an invasive pathogen AND I assumed the bugs were distributing it across my whole collection.

I feared my whole collection might be doomed and many evenings I felt pure dread. I was trying to figure out how I was going to deal with all of this in my living space but I had to start eliminating variables one by one.

I started by eradicating the bugs. I tried it all: dish soap & water, Oil, soap & water, potassium soaps of fatty acids, neem oil (in fact I tried a bunch of different oils: cinnamon, eucalyptus, peppermint, and a few other things I picked up) — I treated weekly, and rotated different things, and while I was able to control them, I just couldn’t kill them all. The infection continued spreading and I was having full-on anxiety about what this would mean about my plant hobby (including my blog and youtube channel). So as one last “hurrah”, I pulled out the big guns: I got Malathion – a super toxic pesticide and applied it on my plants out on my patio…and it worked very well (though don’t breath that shit in if you ever use it – it’s terribly toxic). Malathion nuked pretty much every bug I had and I spot treated with Imicloprid for any surviving bugs. But the symptoms didn’t stop spreading…

It affected more than the orchids

Then something happened that made me stop and go, “What the fuck is going on?!” – one of my non-orchids collapsed (Anthurium forgettii) after a watering and within a few days. A plant that was the fastest to establish and grew leaves that had tripled in size…suddenly turned to a fibrous putty. The newest leaf aborted, and the other leaves shriveled and died…the only thing that remained green was the stem. Then I started noticing things in my other tropical plants. My Monstera adansonii had black spots on every leaf…something I assumed was due to my low humidity, but have since discovered was not.

Old Damaged Leaf
New leaves after stopping use of phosphoric acid

My Philodendron melanochrysum aborted a new leaf, then another – they would turn brown before exiting the sheath and smelled like vinegar and garbage (a common sign of bacterial blight) but the infection never spread into the main stalk or other leaves. My soursop tree wasn’t doing so hot either – it was dropping leaves which were yellow and chloritic, and new leaves were growing smaller and “crinkly” with holes and spots in them (things I originally thought were due to the repot I had performed in spring). For the first time since I was dealing with the phals, I began to wonder if all of these various problems were connected.

These are all the symptoms I noticed – different problems depending on the type of plant

(and many showing up on established plants which I’d owned for over 1-3 years or more):

  • Aggressive yellow-spotting on leaves
  • Virus-like symptoms on the leaves (yellowing in streaks, cell collapse, etc)
  • “Healthy then dead”
  • Leaf spots (some yellow some black) & pitting on many plants that had never had this issue before (bulbophyllum, stapeliads, coelogyne, etc)
  • Slowed/stunted growth of plant, including smaller leaves and a complete halt of root growth
  • Black/Dry roots
  • Dark-green leaves (compared to many that used to have bright green leaves)
  • Crinkled and/or curled leaves on random plants (both orchids and non)
  • Extremely long flower spikes (2-3 feet on select phals…one, phal lowii had an over 2 foot long spike…on leaves that are 4″)
Photos of other affected plants
Extremely long spikes – this was nearly 30″ on a phal lowii w/ 2-4″ leaves
Leaf curl on phalaenopsis
Chlorotic / yellow leaf spot on Phal Penang Girl

I was feeling a creeping urge to hit “eject” and just not have any plants at all because my whole collection seemed to be dying.

A change of perspective

Then in an unrelated discussion about calcium, I ran an experiment testing the solubility of eggshells in various solutions. One was vinegar which as expected completely dissolved the eggshell. Oddly though, the eggshells in my phosphoric acid and tap water solution…didn’t dissolve at all! That didn’t make any sense (acids are supposed to dissolve bicarbonates, that was the whole reason I was using them after all – to combat my alkaline tap water). Fun observation, tap water alone (without phosphoric acid) even dissolved a bit of the eggshell. Something was up. The results of that experiment bounced around in my head for a while. The whole point of adding acid to alkaline water was to make minerals and plant-nutrients more soluble and yet the “pH Down” I was using clearly wasn’t doing that—at least with calcium it wasn’t.

Photo of eggshell experiment testing solubility in water of different pHs

Phosphate Toxicity?

I began to wonder if THAT might be responsible for all of these issues. Even though I had been using pH Down (phosphric acid) for over a year now, the latest bottle I was using was only for the last 3 months…and it was about two-thirds used. I was seeing signs of severe calcium deficiency, zinc deficiency, and iron deficiency and upon some heavy research, I discovered all of theses signs could be symptoms of phosphorus toxicity. You see, too much phosphorus and it starts to lock out other plant nutrients – which explains why I saw so many different symptoms with different plant genra.

I stopped using pH Down (Phosphoric acid) & changed to a blend of organic acids

First, I gave the pH thing a break. I flushed each pot with straight unadjusted tap water and didn’t use any acids for a couple of waterings. I wanted to flush any junk out that remained in the pots. Then, I took quick action and did a deep dive on acid alternatives. I found that all of the following were either used in nature, in horticulture, or both:

  • Vinegar (acetic acid – a biproduct of bacterial & fungal decay)
  • Carbonic acid (carbonated water & an acid found in rain)
  • Citric acid (produced by many plants in alkaline regions to adjust the micro environment around the roots)
  • Humic acid (a group of molecules that bind to, and help plant roots receive, water and nutrients)
  • Fulvic acid (organic acids, natural compounds, and components of the humus)

I bought everything except a Soda Steam (which I’d really like to try one day as carbonic acid is as close as you can get to “natural acid” orchids would get exposed to as epiphytes) and started making my own “pH Down.” An acid that didn’t include any phosphorus.

With Citric & Acetic Acid, things began to change…

  • Within a week, growth tempos accelerated, and many plants started new leaves or roots. Literally within a single week
  • After three weeks, new roots were growing on plants that had literally no visible green root tissue.
    • The soursop’s newest leaves started growing straight.
    • The miracle berry which otherwise seemed unaffected, suddenly grew an additional 30% in height, and roots that never seemed to establish after the repotting, have started to reach the side of the pot and creep down.
  • After a month, new leaves are approaching completion and no longer have the spotting and issues that the old leaves have (however, this is also common with viruses – they only affect older leaves). no new spots have started, and the overall growth rate of my plants have increased substantially.
  • After about 5 weeks I started seeing growth in a few of my phals that had nearly stopped growing for over 6 months. It was just a couple…but today they all have new root tips growing from the old blackened roots. I’m very happy.
Photo of the newest leaf after stopping use of pH Down

Still in-progress

This resolution is still in process and really, until I see how the plants look in 6 months or a year, it will be hard to say for sure that this was the problem. For me though, even though each group of plants had their own set of challenges (from being repotted, to having bugs), the change of conditions which lead to the universal (and quick) improvement, leads me to believe that this was indeed the cause. If you’re using phosphoric acid, I’m not saying to stop, but perhaps be careful about purchasing different brands; and if you’re considering starting to pH-adjust your plant water, maybe save yourself the possible grief associated with some of the phosphoric acid options and opt for more organic acids such as citric acid.

For due diligence, I did test the worst plants for viruses

$200 later, they came back negative

I tested for PotyVirus, CymMV, & OSRV…and all tests were clean.

One other change – pH Cycling

This whole experience kind of gave me a lot to think about with regards to pH, right? Maybe it was the product, maybe it was my watering practice, maybe it was the long-term affect of using phosphoric acid on plants – I don’t know. Today however, I as well as switching to my own version of pH Down, I have also started cycling my watering routine. I use an acidified fertilizer 2 weeks in a row, followed by 2 weeks of un-adjusted tap water.

Because I was using a soluble acid to adjust my pH, it may be possible that it built up in the potting media after repeated use. Imagine that you’re adding a little bit of salt to water and then letting the water evaporate. Then the salt concentration increases in the solution…and if you repeat that process a couple times, then you potentially end up with a salty solution. In the case of pH Down…maybe 2-3 uses without sufficient flushing can easily lead to ultra acidic conditions that drop the media to a pH of 3 or 4. My struggle with this is that it doesn’t answer the eggshell experiment – even if the pH was going super low…why didn’t the phosphoric acid dissolve the eggshell? And if it didn’t dissolve the eggshell…then how was it interacting with my alkaline tap water?


Road to recovery – photos since this all happened

New roots starting from the black roots


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Phal roots on the mend.

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New leaf on my Philodendron melanochrysm (the first non-aborted leaf since this all started)

Monstera adansonii – remember the black spots above? All cleared