9

Somebody just asked me a question that I had a hard time answering, so this is more or less their question which I am repeating.

When it comes to gardening, plants need phosphorus (P). And they asked if it was bad since there are products (say toilet bowl cleaner) that are P free. They figured that the cleaner does not have P because it harms the environment. For me that shouldn't be true since plants need P to reproduce and grow. Maybe it something else?

How should I answer this?

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    I think the answer is strongly affected by political correctness. so I won't say anything. I would use more TSP in the garden but it is more expensive than my regular 9- 45- 15. – blacksmith37 Mar 26 '18 at 20:06
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    Hi Ljk! There is a difference between Phosphorus (P) and Phosphate (PO4?). I think that worrying about excess algae blooms that wouldn't be there at all if we didn't use our rivers as sewers, yet the industrial waste Fluoride was overlooked in the tests? Sigh. Isn't TSP a very gnarly cleaning chemical? I gotta go look... – stormy Mar 26 '18 at 21:10
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    @blacksmith37 yup, TSP is a toilet bowl bathroom cleaner Na3PO4, gnarly oxidizing properties. THIS is what all the hullabaloo is about! And you use this for your garden? Your soil? I'd have to check the chemistry reactions but...how IS your garden? Interesting subject! Brushing some of the dust out of the corners of my attic for sure! I do remember something about taking P out of the formulations of fertilizer because phosphorus wasn't leaching as fast or being taken up as effectively as other chemicals. They were getting lots of excess P problems, questions and in tests. – stormy Mar 26 '18 at 21:20
  • It is good in the dishwasher also. I have very acidic sandy soil; I use TSP on bottle brush and pomegranates because they want alkaline soil. Onion sets also need it in my soil. But azaleas and camellias love the soil. – blacksmith37 Mar 27 '18 at 21:05
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    Sodium is a highly reactive metal that explodes on contact with water and yet is even more vital to life than phosphorus. Chlorine is a chemical weapon yet is also vital for life... – RonJohn Mar 28 '18 at 5:22
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Plants absolutely have a need for phosphorus. Phosphorus is important for plant growth, in particular it's part of the component elements that DNA is made of. Plants short of phosphorus tend to display discolored leaves and stunted development.

Too much phosphorus in the environment is potentially a bad thing though. In particular excessive phosphorus in waterways tends to contribute to harmful algal blooms such as this one in Toledo Ohio that rendered the public water system undrinkable for weeks. Because of this it's a good idea to only use Phosphorus when you need to (ie. when a soil sample indicates it would help), and to limit the amount of your fertilizer that makes its way to a waterway.

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    In short, fertilizing your garden is good. Fertilizing the local river is bad. – Mark Mar 26 '18 at 22:50
  • People absolutely need phosphorus ; look up Krebs Cycle and calcium hydroxyl apatite – blacksmith37 Mar 28 '18 at 15:22
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The problem is scale. We fertilize our gardens to a specific effect. When phosphorus and nitrogen from laundry detergent and other types of cleaners is let go into the environment in massive quantities it has a tendency to encourage algae growth in to the detriment of nearly everything else, including animals.

It chronic, it can then lead to low levels of oxygen in the water, further impacting other species.

Everything in moderation! Don't water your garden with 1000 gallons of fertilized water.

7

Yes, phosphorus is essential to plants. It's important for humans, too (in moderation), but it's one of the three major components of fertilizer for plants (the P in N-P-K). Phosphorus helps with flowering, roots, photosynthesis, cold-tolerance, plant maturity, leaf size, etc.

The major concerns I've heard about phosphorus are with supplemental phosphorus (as opposed to phosphorus naturally in the ground), and are environmental, and ethical, but there are some health concerns, too. It all depends on what kind of phosphorus you're talking about. It's pretty difficult to find supplemental phosphorus that everyone can agree is healthy, fine for the environment, etc., including when it comes to organic forms of supplemental phosphorus.

Sources of phosphorus (including organic and non-organic forms):

  • Bat guano: this sounds like it works great, and is organic, but people worry the harvesting of it is harmful to the existence of the bats.
  • Super triple phosphate (it has a lot of names): it may be contaminated with fluoride, which may cause issues with plants, and potentially with people, too; I believe it's water soluble (not sure), and may leach into the water table if used in high amounts; there are other ethical issues with this and phosphoric acid production, but I don't want to delve into that, since I don't have all the facts and what is and isn't fact with me (nor does probably anyone). However, if you look up the phosphorus industry you may find some stuff. stormy shared a video in the garden shed about it.
  • Bone meal: The animals may or may not have been given stuff you don't want in your garden.
  • Wood ash: Although I personally don't think it's a significant amount, and I love using wood ash, they do contain some heavy metals. Wood ash has about twice as much potassium as phosphorus, however, and a lot of calcium by comparison (so it can raise soil pH).
  • Monopotassium phosphate (if phosphoric acid is used to make it, then the fluoride issue may exist here, too, but I don't know if that's an issue; it's water soluble—so it may leach into the water table if used in large amounts; if you've got clay soil, I imagine the leaching isn't as huge of an issue; I've used this with good results, although I'm still wondering how much fluoride is in it, if any; it has a lot of potassium in it, too)
  • Monoammonium phosphate (ditto, except it has a little nitrogen in it instead of any potassium)
  • Compost: People don't generally go on about how bad compost is, but it's only as safe as what your compost is made out of. If you put organic waste in it covered in pesticides and herbicides, you might have the same issues as with the bone meal.
  • Worm castings: these aren't really a phosphorus source, but they may contain microbes to help make existing phosphorus in the soil more available. I could be wrong about that (since maybe I'm not remembering right): maybe it was mycorrhizae that did that, but worm castings may have mycorrhizae in them for all I know.

Water pollution is a concern with water soluble phosphorus; so, that may be what people are concerned about with the toilet cleaner.

Anyway, my source is just research all over the Internet, which I've done the last few years. It's not all indisputable, but this is what I recall.

In reading the claims against forms of phosphorus in this answer, be careful not to assume that I take any particular stance on any particular thing I was talking about (with the exception of wood ash, which I think is great stuff, despite claims against it).

  • Well said! I have used worm castings in the past and as I recall they do supply K, but all the elemental compounds (N-P-K) occur in different concentrations in different studies/samples. It is apparently used primarily for the N content. Good stuff! – Tim Nevins Mar 27 '18 at 20:10
  • There is pretty much one significant source of phosphoric acid in North America - Florida. s – blacksmith37 Mar 27 '18 at 21:33
4

Great answers, I just add a note:

Phosphor pollutes the environment (water systems) because it is a fertilizer: Phosphor fertilize the algae (which is good), the algae eventually die (this is natural), algae decompose (bacteria like it), decomposition take oxygen (bad bacteria), fishes and other animals in water will suffer or die (bad phosphor!).

But as fertilizer, it should not be a problem, but if you have ground water: every movement of phosphor will fertilize plants (and not algea), so when fertilize reach water, it should have no more phosphor.

  • So the moral of the story is ; do not buy a bag of fertilizer and dump it in a lake ........unless you are growing catfish . I can't remember the specifics , but catfish farms sometime throw fertilizer into the ponds. – blacksmith37 Mar 27 '18 at 21:15
  • @blacksmith37: In general: never bump a fertilizer. Like food and medicines: too much is bad (and often toxic). We need an equilibrium to have a nice garden (fertilizer total, but also by component, according different plant needs). – Giacomo Catenazzi Mar 28 '18 at 5:38
  • I guess we should tell catfish farmers. – blacksmith37 Mar 29 '18 at 14:05

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